Joined: November 24, 2008
Location: Des moines Iowa
|Posted: Tue Jun 28, 2016 3:54 pm Post subject: Type 3 and 4 front caliper rebuild "how-to" part 1 and 2
|Brake caliper rebuild.
So….Just to start. There is no reason for all owners NOT to rebuild their own calipers. You will get as good or better results than any remanufacturing house….as long as you are clean, use a good kit, and do a complete rebuild…and observe a few rules that mainly have to do with deciding if a caliper is rebuildable at all.
PLEASE READ THIS IF NOTHING ELSE: If you must skim the long written information section of this “how-to” before beginning….at least read all of my warnings FIRST. They are bold and in red.
IMPORTANT NOTE:Please take the time to read all of this before you start. I know it’s a lot of reading right off, but I am putting all the details in that I can so that those who are afraid of brakes will have more information to start with and fewer unanswered questions.
Do not just skip to the pictures! Most people do not rebuild their own brake components out of fear of making an error that will compromise safety. With calipers this is actually very hard to do.
As long as you are clean, use quality parts and above all do not” jury-rig” parts, do not use untried or suspect techniques to cut corners and do use proper judgement when evaluating whether a part can be rebuilt or should be discarded, your rebuild will be perfectly safe and have original functionality.
DISCLAIMER: There are certain items I do when rebuilding heavily worn calipers that are modifications. They are excellent and safe modifications but will be noted as “non-standard”.
Why should I rebuild my calipers instead of just buying some?
• Short of Concours level “restored” calipers, the very best remanufactured calipers may have either new pistons and/or replated bores to put worn out corroded parts back to original specifications but that varies from caliper to caliper so you may never know and outside of that the performance and longevity will be no different than what you rebuild..…as long as your core is rebuildable in the first place.
This becomes partly a cost issue. If the remanufacturer of the caliper has gone that far (replacing pistons and replating an old piston or bore) it’s going to be in the $150 + range per caliper. Companies like A1 Cardone “used” to make mass-remanufactured calipers like that about 25 years ago. Not common anymore.
• To add to this, many budget calipers from mass rebuilder houses have been showing up with oversized parts and seals that have been added as the remanufacturing houses do machine work to utilize caliper casting cores that are beyond normal rebuilding.
On one hand you have to respect the fact that they went that far in effort….but in rare cases I have found calipers that utilize mix and match halves wherein one piston now uses a different seal than the other. This makes future rebuilding an issue.
• Any other better basic rebuilds (Raybestos, Beck Arnley etc.) will be bulk stripped, solvent vatted for grease removal and probably bead blasted. You may get mixed caliper halves which generally is not a huge problem but can be sometimes as machine angles can be off. We have seen on some remanufactured parts.
These calipers will range from $45-$85 give or take and may come with pads (listed as friction ready)..…which should not sway your judgment unless you get to choose the brand and friction material (you do not). Most of these have basic paint on the outside, a seal kit and are no better than what you will be building except I have found a great many to be filthy inside.
Many still have basic core issues like poor fitting clamp bolt threads, oversized re-tapped bleeder screws and cheap hardware. If you are getting a rebuilt caliper in the $45 to $85 range WITH new hardware AND a $20 set of pads….you have to ask how much labor, time and inspection went into rebuilding it and $20 pads are rarely top notch.
• In short, rebuilding the calipers yourself gives you the best balance of value which includes: allowing you to choose the best quality parts, know the caliper is clean inside and out and has a 100% known quantity of performance.
It also allows you to choose top notch coatings to aid longevity as well as to make small improvements in parts that are far better than what you can get in a basic remanufactured caliper (like new larger, stronger bolts and speed bleeder screws or regular bleeder screws of factory level quality).
Lastly, if it does not work when you install it…you know what the problem is NOT.
• At 30-40 years past the original build date, good original cores for the rebuilding houses are getting hard to find. This makes perfect rebuilds harder to get. Yes, companies like Centric are making new castings which may or may not be as good (jury is still out) but you will also have to have their rebuild kit to use them.
An important part of this process is preserving original castings by rebuilding them properly so that they operate well, survive and continue to be rebuildable in the future. If you treat the calipers well by changing fluid regularly and rebuilding them before they are trashed, they will last forever.
What is the cost?
First off, there is total gross outlay versus REAL net, per-caliper cost. There are some items I will not count in cost because you should have some of these already (mostly tools).
Secondly, in cases where you have to order hardware like the bag of ten 8mm bolts (when you only need eight) and the bag of 8mm Schnoor washers….I am going to discount that total cost to only parts and shipping used…because a bag of 100 Schnoor washers is the only way they come from McMaster Carr and at $11.71 plus average $5.50 shipping for a bag of 100 (divide that shipping cost by two if you are buying the bolts at the same time) equals about 14 cents per lock washer and these washers are used all over your car from CV bolts to engine and transmission case bolts and you can always find a use for two spare 8mm bolts. It’s the cost of doing business.
If you can get these bolts and washers locally at Ace or Tru-Value hardware…where they cost 3X as much, you may save a little money but not much. Usually it’s about equal with no shipping.
The solvents and chemicals I also discount because all of these are chemicals you will use the rest of elsewhere to defray actual cost to calipers. You will use about half of these chemicals volume. The safety equipment cost I do not count at all….if you don’t have safety glasses, good ventilation, splash goggles, nitrile gloves, a basic respirator and a cheap fire extinguisher…..stop working on cars before you kill or maim yourself or someone else.
Drill bits and taps and consumable cutting tool bits like Dremel brushes I count.
Cost for my rebuild:
Tools: $25 (two taps, dill bit, Dremel brushes)
Chemicals: $30 (MEK, Muriatic acid, aircraft stripper and 1 can of Berrymans carb cleaner. I have a parts washer that did much of the grunt work). I had plenty left over of everything.
Parts: $119 (caliper kits, caliper half seals, hardware kits, bolts, washers, speed bleeder screws and about $4.50 worth of caliper lubricant….I bought the expensive Porsche paste but it will do about 20 caliper sets)
Paint: $14 for two cans of VHT caliper paint
Abrasive paper and 3M scrubbers: $6
Gross total: About $234 total outlay for parts and materials (about $41 of which I still have for other uses)
Net total: $194 for two calipers= $97 each
Time factor required:
Not counting solvent soaking time and paint stripper soaking time and paint dry and baking time, actual labor time for each caliper for disassembly, cleaning, stripping, painting/masking, reassembly was right at four hours per caliper.
This is a good weekend project. About 1-2 hours on Friday night getting these into the solvent bucket. You can do most of the serious scrubbing in this period. About three hours on Saturday and three hours on Sunday with the drying and other periods in between and you can assemble Sunday night.
What constitutes a rebuildable caliper core?
Outside of corrosion damage and deep scoring of the piston or deep scoring of the cylinder that covers a major uninterrupted swath of the cylinder wall, almost all calipers I have found are rebuildable to operate perfectly just like the day they left the factory.
A list of issues that make a caliper or some of its parts NOT rebuildable:
1. Deep pitting or scratches on the piston: that are deeper than about .002”-003”…and span a length longer than the rubber sealing ring is wide. You will have to estimate that depth unless you have a dial indicator with a needle tip attachment to measure the depth of a pit next to the undisturbed plating.
2. Wide area cylinder pitting: Serious wide arcs of cylinder pitting more than .005” deep on the cylinder wall….that span more than 20% or about 72°continuous arc of the 360° circumference of the cylinder.
This is actually not very common but when it is you will be able to feel the piston chatter or move sideways in the clean bore in one direction more than others when the piston is installed without the seal. This diagram may help.
3. Piston physical damage: Pistons where the whole upper ring, not just the thin flange have cracked away so that the boot cannot be sealed around the piston. This typically happens when a previous rebuilder trying to free a stuck piston has used Vise Grip pliers.
4. Caliper half mating area Damage: If any of the mating surfaces between the caliper halves in the seal area are seriously rusted or have been gouged or dented where it creates high points that cannot be smoothed down level with the use of machinist dye or Sharpie pen, a sheet of glass and lapping the caliper body…. cannot be used.
5. When piston to bore clearance is greater than .005”: either from rust or previous honing. Typical piston to bore tolerance in most steel piston calipers is .002” to .005”. For reference, aluminum pistons tolerance can range to .008” to .010”. Phenolic pistons from about .010” to .012”
NOTE: you can “generally” rebuild and safely use a caliper than has piston to bore tolerances as high as .007” or even a bit more without leakage issues, however these will usually be noisy and wear quickly because the excessive tolerance makes for difficulty retracting the piston properly when you let off the brake due to the level of extension of the rubber seal. However for reliability I do not use anything over .005” tolerance in these types of caliper.
6. Cylinder wall rust pitting: that has an uninterrupted span starting on the cylinder wall below the seal groove, passing through the seal groove and out of the seal groove into the top piston guide area. This can let fluid bypass the ring on the backside. Again…about .001” to .002” just barely roughened surface of a rust pit can be usable but when it gets to be about .005” or deeper it’s too much.
7. The pistons are chrome plated/damaged plating: If any of the plating is chipping and missing, the piston cannot be used without some work.
NOTE: This can be fixed….if the cylinder to bore tolerance is in the low range like .002”-.003” and the piston is not dented or gouged like from Vise Grip pliers or C-clamp use where the chrome is missing. To accomplish this, the plating is stripped with muriatic acid.
This makes the piston roughly .001-.002” smaller in diameter. A rubber expansion plug and bolt is then inserted into the piston cavity, chucked into a drill and running a loop of 2000 and then 3000 grit wet/dry paper will polish the piston to an acceptable finish in just a few minutes. As long as it is within diameter tolerance it will perform perfectly, however it will now be less resistant to rust so the brake fluid must be serviced yearly to prevent rusting.
8. Broken caliper half bolts: because they are rusted in can make the caliper non-rebuildable….if you either cannot get them out or if you damage the caliper while getting them out. I have not had one like that in a long time.
One of the main modifications in this rebuild is re-tapping the odd 7mm bolts to 8mm. Not only are they stronger, you now have the opportunity to install bolts that are easier to replace if necessary, have clean threads and you can add a small amount of anti-seize to make sure they stay that way.
9. BROKEN OFF BLEEDER VALVES: This is one of the primary issues…and one we will deal with specifically first as part of evaluation. It is easiest to deal with this before disassembling.
WARNING: Brake calipers are very easy to rebuild, but success is about cleanliness, completeness of build and not cutting any corners with judgment regarding whether a part should be used or not. When I say cleanliness I also mean that the calipers in my experience and opinion should be completely disassembled, stripped and cleaned. After 40+ years, you cannot fully evaluate them or get the parts clean enough without full disassembly and removing all coatings.
Levels of rebuilding/Restoration:
From experience and research, there are several levels of caliper rebuilding…all of which are EQUALLY serviceable with no differences in performance but with differing levels of cost and complexity.
This is my best method in this outline and to insure safety and success, gather all the tools and chemicals and do not experiment unless you know how an added material or chemical will perform.
Levels of caliper rebuilding:
• High quality complete basic rebuild (this is what we will be doing): Stripped, cleaned, all parts measured and checked, rust and corrosion removal, cylinder and piston polish or lapping, all consumable parts replaced (seal kit, caliper half seals, dust boots, all new hardware, bleeder screws, new lock washers, piston anti-rotation plates, brake assembly paste and high temp caliper paint or coating)
• Repair of damaged caliper casting full rebuild/restoration: All of the items in a high quality basic rebuild plus either piston replacement if necessary and/or sleeving of the cylinder if necessary. This is fairly expensive.
This may include welding up of damaged threaded areas like bleeder valve and assembly bolts and rethreading and machining.
It should be a very RARE caliper to go to this trouble and expense (like very old, Porsche, Ferrari etc…meaning unobtanium). An example of companies that do this are Apple Hydraulics www.applehydraulics.com
• Concours level restoration: Has all of the items in the high quality basic rebuild with the addition of re-plating with chrome the original piston or replacing it with NOS, restoration and machining and plating of the cylinder bore to bring it back to exact stock specifications, factory paint type and color for the caliper and NOS or factory hardware, bleeder screws etc. Essentially it’s a full factory restoration.
In some cases for some cars, the caliper may have originally been cad plated or yellow zinc, so replating of the entire caliper and matching factory shade of plating color is done. At one point in time there were people who did this in the Porsche community for fairly cheap….but typically not anymore.
NOTE: This last type or restoration is fairly common in the Porsche, Mercedes and BMW community for full restoration and period exact cars. While I HIGHLY respect the workmanship that doing this level of restoration entails, I also find it to be worthless cost and effort for ANYTHING other than a Concours restoration vehicle.
Even though it essentially makes the caliper brand new like the day it was originally manufactured (in function and appearance), it has “0” advantage in actual function compared to a normal high quality rebuild….and….it will wear at the same rate and not last any longer than any other rebuild but the cost for this level of rebuild can easily be over $500 per caliper.
Tools, Parts and supplies:
Note: many of these items you can find local substitutes for. I will note when you should not.
• A vise or at minimum a work bench with several large and medium C-clamps.
• 6” or 8” C-clamps
• Compressed air with blower nozzle
• Metric sockets and Allen keys (13mm, 12mm, 7mm, 8mm sockets, 8mm Allen Key)
• Torque wrench (beam style is best for this application
• 1/8” flat faced punch
• Ball peen hammer
• Electric hand drill or drill press
• Wood blocks ranging from ¾” thick to 2” thick.
• O-ring picks
• Drill sized 6.75mm or “H” which equals 0.2660”. A 17/64” drill bit can be used but you must be careful and use a sharp tap.
• 8mm x 1.25 tap with a tapping tool holder. Uncoated, bright three or four flute tapered starter taps are excellent. Since this is a through hole we will be tapping, pointed bullet taps can be used. Titanium coated taps can be used but are not as good for this material but will work fine with care. Avoid carbide taps.
You should get two taps. First a “starter” tap which will have 7-10 taper threads or a “through-hole tap” with 3-5 tapered threads….but not both. And get a bottoming tap.
McMaster Carr Part #’s
Starting tap: 8305A19 =$7.69 each
Through hole tap: 8305A38 = $7.69 each
Bottoming tap: 8305A59= $7.69 each
6.7mm drill bit = 30565A291= $3.79 each
• Lapping tool and 800, 1000, 2000 grit wet/dry paper (optional is 3000 grit). We will be making this tool and you will need a 41mm or 1”-5/8” wood hole saw, a 6” length of ¼” x 20 threaded rod two nuts and two washers. Steel wool of “000” minimum or “0000” can be used on the piston if you are more comfortable with using it and the piston is in near perfect condition.
• You can also use a 42-45mm brush style abrasive nylon bore brush like these from Brush research. http://www.brushresearch.com/brushes.php?c1=50 They are about $18 each and have 500 grit aluminum oxide. You are looking for the 1.75”, Series 85-AY standard deburring tools for blind holes. , 600-800 grit, silicon carbide brush.
WARNING: Bear in mind that even though these brushes work very well, you will need to trim the bottom of the wire loop they are made with so that they bottom out in the caliper bore…AND…you will need to leave the old seal in the groove while you clean the bore. Also…500 grit is not that fine so proceed slowly or you can oversize the bore.
• Exacto knife or hobby knife with sharp/new blades.
• Brass, nylon and stainless steel cleaning brushes (Harbor Freight cheap three brush set…get two).
• Disposable synthetic 1” wide paint brushes for stripper. Should be about $1 or less.
• Dremel tool with stainless wire wheels and sanding drums. You can use carbon steel but there is a spark risk with those.
• The use of an oven that can hit 250°F for an hour for baking the paint.
• Telescoping gauges for measuring the bore and a 2”micrometer with .001” tolerance at best or in a pinch if you are careful a dial caliper can be used if you measure carefully.
• Pipe cleaners and/or 1/8” brass wire bore brushes.
• A hot, fast evaporating solvent like MEK, Acetone or Berrymans B-12 Chemtool or a fast drying carb cleaner. Denatured alcohol can be used for some final degreasing and wiping but is NOT acceptable for what we need. One quart will be fine
• A slow but powerful solvent like xylene or a xylene based paint thinner or at minimum Stoddard solvent. One quart will be fine
• Muriatic acid. One quart will be fine
• Polyethylene buckets or ceramic, glass or stainless steel pots or bowls large enough to submerge one half of a caliper in without using an excessive amount of liquid.
• One quart aircraft stripper. Any brand that is gel consistency and Methylene Chloride based.
• Two cans of VHT high temperature caliper paint.
• Ospho phosphoric acid rust treatment or Jasco Metal Prep and Prime or similar product.
• Two 2-gallon zip-lock plastic bags
• Caliper rebuild kit:
BEST DEAL: PMB Performance has all things 914 brake related (which means 411/412 and late type 3 as well).
These kits are complete with all locking hardware, new bolts, seals, dust seals, anti-rotation plates…AND caliper half seals.
1970-1972 http://www.pmbperformance.com/catalog/item/1925563/4747234.htm On sale 6-23-2016 for $17.95 per caliper kit
1973-1976 http://www.pmbperformance.com/catalog/item/1925563/8698978.htm On sale 6-23-2016 for $23 per caliper kit
NEXT BEST DEAL:
Try Rockauto for Centric part #14333008. This is a complete kit for one caliper: seal, dust boot, bolt locking hardware, new caliper mount bolts and new ant-rotation plates. These are repackaged, German FAG parts. This kit is a bargain at $24.79
NOTE: these kits DO NOT have the caliper half seals. Look below at Auto Atlanta for those.
• New caliper half O-rings: Auto Atlanta (four needed @$2.53 each) http://www.autoatlanta.com/Porsche-Caliper-Half-Seal-O-Ring-914-6-Parts-PN-R90135192800.html
• Caliper hardware kit: Rockauto Centric part # 11733007. This is repackaged Wagner or Carlson hardware. New, zinc plated pins and springs. At $7.00 caliper they are a bargain.
• Brake assembly paste or lubricant.
1. DO NOT USE BRAKE FLUID TO ASSEMBLE YOUR CALIPERS….UNLESS… you are going to install and bleed it within 24-48 hours. It WILL start rusting inside. If these will sit anywhere for over a day or two, use brake paste. As an outside limit…one week with brake fluid is all these parts can handle before you install and bleed the system.
If you must wait a long period and have no assembly lube….put the metal caliper parts in baggies unassembled and lubed with oil until ready to clean, assemble and install.
2. When buying a brake assembly fluid or paste, MAKE SURE it is FOR INTERNAL HYDRAULIC PARTS ONLY.
People on many internet automotive forums are mistakenly using external high temp, silicone caliper SLIDE grease for caliper internal assembly grease. Petroleum or synthetic/silicone grease must never come in contact with brake fluid. They will not dissolve in the fluid.
For example: ALL of the brake assembly lubricants listed on the Pelican parts site are external lubricants only and not to be used for assembling pistons and seals.
Also….DO NOT use Molykote 111. The patrons of the Ferrari site list this. It CANNOT be used. It is silicone O-ring grease….great for an air cylinder and for air cylinders or O-rings in bores but will NOT dissolve in DOT 3/4 fluid.
WARNING!!!...in dozens of forums people are discussing using various O-ring lubricants like Dow Corning DC-4 because they do not attack the rubber seals. While the compatibility with the EPDM seal rubber is correct….the worry is not seal compatibility it is BRAKE FLUID compatibility we are worried about. These seals are NOT O-rings operating in a dry bore. There are no O-ring lubricants that are compatible with brake/hydraulic work. Use one of the proper lubricants I list here or brake fluid ONLY!
Many people get away with using improper O-ring grease because the quantity used is so small and the caliper and wheel cylinders are at the end of the line and the grease cannot affect much in that area.…which is why they think it works fine. But….the risky issue where most screw up is using it also to assemble the master cylinder. In that usage, since it never dissolves it plugs the compensation ports behind the flap valves preventing fluid flow in the system (brakes can fail) or making it unable to be bled.
Several good choices here for assembly lube:
Raybestos BAF-12 https://www.amazon.com/Raybestos-BAF12-Brake-Asembly-Fluid/dp/B001ANJ2GE
ATE brake cylinder assembly paste: http://www.ate-info.de/en/products/datasheet/ate-bremszylinder-paste-180-ml/ Virtually impossible to find in the US but the right stuff.
CAUTION: This paste is hard to find. However there is an easy to find version of ATE caliper assembly paste that is INCORRECT.
It is high temp EXTERNAL caliper slide grease and NOT to be used on the internal seals. Make sure what you buy matches the name and visual description of the picture here.
Centric 500.10000 brake assembly fluid. https://www.amazon.com/Centric-500-1000-Brake-Asse...entries*=0
Porsche 000 043 117 caliper assembly paste. Auto Atlanta http://www.autoatlanta.com/results.php?partnumber2...kes/Wheels Very expensive but factory correct if that matters to you.
WARNING NOTE: Real brake hydraulic cylinder assembly lubricants are generally either a coal tar oil based, or natural organic based or synthetic ester based….but designed to be compatible and dissolvable in glycol ether based brake fluid. The Porsche paste smells horrendous like a fish oil. The original ATE paste smells bad as well like a mixture of creosote and diesel. When in doubt, take a small smear of the lube and dip it in brake fluid and rub it. It should dissolve cleanly.
• Brake bleeder screw rubber caps: original equipment ATE “beehive” caps http://www.pmbperformance.com/catalog/item/1925563/4747241.htm pricey but original
• Brake bleeder screws. The 411/412 and 914 use longer versions of the 7mm x 1.0 bleeder screw.
BEST: Speed Bleeder brand. http://www.speedbleeder.com/
http://www.speedbleeder.com/size.htm Pictures and information and they come with rubber caps for the bleeder screws.
Part # SB7100
VERY GOOD: These are a bargain and have the larger 8mm hex on them http://www.pmbperformance.com/catalog/item/1925563/9594710.htm
Good enough: Raybestos part # S23928 Rockauto has these for $1.55 each but they only sell them in packs of 10. Many other people sell this part # as well.
WARNING DO NOT USE: any of the Dorman Brand bleeder screws until I figure this one out. The only part # they list is the short one that has interference issues with the bolts (though it is usable) on the caliper and also has also lately had the wrong angle ground on the sealing tip and does not seal and is therefore defective.
• Caliper bolts: McMaster Carr
8mm x 1.25 X 70mm uncoated class 10.9, full thread package of 10- Part # 91310A133 for $7.51
• 8mm or 5/16” Schnoor ribbed Bellville lock washers. Black coated steel package of 100- part # 93501A030 for $11.71
SAFETY EQUIPMENT WARNING:
• Safety equipment:
If you are going to be stripping with muriatic acid (which I highly recommend especially if you have no access to bead blasting):
VERY IMPORTANT: Respirator with combination acid gas/organic vapor cartridges.
NOTE: these will have a yellow/gold decal and be listed as OV/AG (this stands for organic vapor and acid gasses). Typically these have a magenta or purple cap and yellow decal on them.
Fan for cross ventilation
Garden hose with sprayer nozzle so it can be left running and close at hand
2 lb. box of baking soda
1 gallon water bucket filled with water and 1 pound of baking soda dissolved in it.
An outside work area
For general solvent usage:
Nitrile gloves (Favorite brand available at Autozone) are the MicroFlex “MidKnight” gloves. Nitrile, fully textured, 4.7 mil thickness, black
Respirator with combination acid/VOC cartridges
Fan for cross ventilation
Garden hose with sprayer nozzle so it can be left running and close at hand
Air hose with blower nozzle
For aircraft stripper usage:
All of the above and one pair of thick Butyl or Neoprene gloves. The Aircraft stripper will eat Nitrile or latex gloves in under a minute.
The ones I use are excellent for most any solvent wash tank and most chemicals you will come in contact with from muriatic acid to Methylene chloride in the concentrations you find in aircraft stripper (but not straight undiluted Methylene chloride).
They are Ansell Edmont “Scorpio” series # 08-352. They are seamless, cotton lined and are butyl rubber with a neoprene outer dip coating. I bought them at Menards. You can get equivalent at Home Depot and many welding supply houses or on Amazon. They will last a long time (these are two years old). Should be about $6-$12 a pair depending on where you buy them.
Part 2 coming up Ray
Last edited by raygreenwood on Wed Jun 29, 2016 12:00 pm; edited 1 time in total
Joined: October 04, 2007
|Posted: Wed Jun 29, 2016 1:35 am Post subject: Re: Type 3 and 4 front caliper rebuild "how-to" part 1
|Just love your how-to's Ray, thanks again!!!
Porsche 914 -72, Bahia Red daily driver
VW411 2-d -70, White, sold
VW412 4-d, -73, Gold Metallic, daily driver
Suzuki T500, -69, Candy Gold, sold
Suzuki K50, -77, Black, daily driver
BMW R69S -69, White, sold
Husqvarna 118cc, -47, Black, in archive
Joined: November 24, 2008
Location: Des moines Iowa
|Posted: Wed Jun 29, 2016 9:20 am Post subject: Re: Type 3 and 4 front caliper rebuild "how-to" part 1 and 2
|There are a few additions.....
Do not discard any of the old parts until after the new parts arrive and you have completely finished the caliper rebuild. Some of the old parts like pins and tension springs may be of better quality than some new parts. If they are in good shape and can be cleaned up they are good spares.
Also it’s not uncommon for early and late hardware to be mixed up. They do not trade across seven though the caliper seals do. More than once I have had to get back on the road with old hardware.
Caliper cleaning and stripping:
A walk around. Filthy and surface rust.
I rebuilt these once already about 18 years ago. Note that this caliper has a mixture of parts. It has a single speed bleeder that was in the top position, a single factory long style bleeder in the lower position, it has a single 7mm bolt with 8mm Allen wrench head from either an earlier type 4 or type 3 caliper and three of the 7mm factory hex head bolts with 12mm socket hex. I had broken a bolt on the last rebuild and had to use one from an early caliper because 7mm bolts are hard to come by.
First step is just to remove the hardware and outer boot. Use the 1/8” punch to remove both pins, the pads and tension spring.
Remove the anti-rotation plates….and SAVE them even though your kit has new ones.
Remove the seals and spray some penetrating oil on the piston and let it soak for a while. Also put penetrating oil into the caliper through the fluid access port to soak from both sides.
The caliper is mounted in a padded jaw vise. You can put bolts in the mounting ears and clamp it to a work bench as well. You can see the red compressed air nozzle in the foreground. This is a piece of 1” x 1” wood between the pistons.
It’s very common that only one piston comes out. When that happens, put some extra penetrating oil on the one that came out and push it back into the bore. Then clamp it into the bore with a 6”-8” C-clamp.
Apply air pressure again. Usually with some tapping on the caliper body, penetrating oil and more compressed air, the stuck piston will pop out. Be patient. Wear safety glasses, use the wood block and keep your fingers out of the way of the pistons.
Then flush away rust and dirt from the piston that originally stuck with solvent and then lube the stuck piston with penetrating oil and push it back into the bore. Remove the C-clamp from the free piston, put the wood block back in and blow both pistons out with compressed air. You may need to change to a very thin stick of wood to get both pistons far enough out of the bore to wiggle them free.
WARNING: DO NOT SPLIT THE CALIPERS APART YET!
You can split them as I did to inspect to see if there is any damage that would preclude using them as a rebuildable core, but reassemble them for cleaning.
The still assembled calipers are easier to handle for de-rusting and cleaning without damaging the mating surfaces if they are assembled.
IMPORTANT NOTE: If you are going to be bead blasting or soda blasting, remove the seals from inside of the calipers and lubricate the pistons with wheel bearing grease to hold them in and keep debris out and reinstall them so that the bead blasting does not damage the piston, bore or leave debris in the passages.
Yes, you can bead blast the bores if they are crusty but you will still have to lap them smooth. Be careful and do not get carried away.
DO NOT bead blast the pistons. If the chrome plating is not perfect but is serviceable, bead blasting will damage it by exploiting scratches in the plating.
General chemical cleaning:
I provided no pictures of this. It was far too messy of a process to use delicate camera equipment around. But I will provide a play-by-play.
• Re-assembled calipers with pistons removed are soaked in basic solvent (paint thinner, Stoddard/parts washer solvent etc.) for a night. You can do this in a plastic bucket with a lid. Keep this dirty solvent. You will use it again.
• Several times during soaking, brush the calipers with the wire brush in all areas to remove baked on layers of brakes dust, flaky paint and road grime.
• Remove calipers and blow dry with compressed air. Move to a work table or surface for messy work with a large plastic trash bag covering the work surface.
• Pour approximately 6-8 ounces of Aircraft stripper gel into a glass, polyethylene plastic or ceramic dish. Do not pour out excessive amounts. The volatile working chemicals evaporate fast. Add more as you need so you do not have to pour it back into the can.
• Using the 1” paint brush, work the stripper onto every surface of the caliper and scrub stubborn areas with the wire brush and Scotch Brite pads…but beware the pads will dissolve so only use them when they are needed.
• Place the calipers into the two gallon zip lock bags so that they stay wet. Follow directions on the stripper for soak time.
• Remove calipers and transfer to the dirty solvent bucket and scrub away the crud with the nylon and wire brushes. Wipe up excess with paper towels, blow dry with compressed air and inspect.
• Use the Dremel or a die grinder with wire wheel where needed to remove thick areas of paint and brake dust build up. Wear your safety glasses and respirator.
• Repeat the stripper process as needed. It usually takes two treatments.
At this point it should be bare metal. Work hard at this. Get them clean.
This is excellent for COMPLETELY removing ALL rust. It will not damage any of the steel.
WARNING: You need the live Garden hose, a bucket of baking soda and water mixture on hand but out of the way, a glass or ceramic dish, cross ventilation, nitrile gloves, splash goggles and your respirator with OV/AG cartridges and one of the cheap disposable paint brushes
WARNING: You will be using straight acid here. But when you are cleaning up or if you decide to dilute some acid….YOU MUST ADD ACID TO WATER…NEVER WATER TO ACID OR IT CAN REACT VIOLENTLY.
NOTE 1: If you are going to acid wash, split the calipers apart now and Keep the parts separate. Work on one caliper at a time. This lessens the possibility that you will drop a slick caliper complete into a dish causing a large splash or breaking the dish and poring acid everywhere.
NOTE 2: If you have broken bleeder screws to remove do this before you acid wash (next chapter).
NOTE 3: if you acid wash you should use a phosphoric acid rust converter as well. The flash rust produced by the acid is perfect for converting and the converted rust is perfect for paint primer.
• Split the calipers apart
• Place each DRY caliper one at a time in a gallon plastic bucket or a wide STEEL pan (use no aluminum dishes or tools)
• Pour about 8 ounces of muriatic acid into a glass or ceramic bowl and dip the paint brush into it.
• Brush the caliper on all surfaces. The rust will fizz, foam and smoke.
• Use nylon and steel small bore brushes or pipe cleaners to run the acid through all of the bolt holes, fluid channels and ports.
• When you are done, rinse the caliper with the garden hose.
• Repeat if necessary.
• Then dip the caliper in the bucket of baking soda and water, rubbing all surfaces with your gloved hand. It will fizz a little as the acid neutralizes.
• Rinse with the garden hose.
• Oil liberally with WD-40 and blow dry with compressed air.
IMPORTANT NOTE: if you are planning to use a phosphoric acid rust neutralizing coating/primer before painting.…which I highly recommend…..only oil the inside bores and let the caliper castings flash rust.
• Rinse the paint brush with water. Dip it in baking soda and water and when it stops fizzing throw it in the trash.
• Add water into the remaining acid in the dish. Add at least 60% water volume to it. Slowly dribble this into the baking soda and water bucket. It will foam heavily.
• When it settles down, rinse the bowls in the baking soda and water mixture to neutralize and rinse with plain water and dry them.
Broken bleeder screws:
Since this is part of inspection and evaluation lets deal with it now. Bleeder screws snap off because they are rusted in.
Part of the cause of this with the OEM bleeder screws (part # 311 615 273) and many others is that the outer bore of the screws is larger in diameter than the threaded section.
This makes it weaker so it twists off when the threads rust tight. You can see in the above pictures of the stock bleeder screw, the drill bit only goes in to just a little past the wrench hex.
How to prevent bleeder screws from breaking off (prevention is the best way to fix them):
1. Use good quality bleeder screws. The original part # is very hard to find in the US. Dorman products (most common) does not list a correct part #. The vendors generally sell part # 13905 which is not acceptable (improper length and tip angle).
The correct part VW part number can sometimes be ordered from Pelican Parts but is not in regular stock. Expect similar cost to Speed Bleeder screws. The Raybestos screw listed below is the exact same shape as the factory screw....but has a different finish.
Auto Atlanta and PMB performance are also sources. Or you can use Speed Bleeder brand which are excellent. The very common Raybestos part # S23928 are very good. They are generally the correct length and are fairly good copy of the long hex factory screw.
2. Use a very small amount of anti-seize compound on the threads ONLY. Or if you use speed bleeders they come with a thread sealant so no anti-seize is necessary.
3. After each bleeding, wash the fluid out of the bleeders and off the outer threads with water from a hose or squirt bottle and blow dry with compressed air…and above all put a bleeder screw cap on them.
Removing broken bleeder screws:
I had no broken bleeder screws to demonstrate with but will explain the two best ways. There are lots of versions of this but my method works very well.
1. Step drilling the broken bleeder and dissolving the rust and then using an easy-out:
This is the best/easiest way I have found but takes a little patience and time. The drawback is that if the threads in the caliper are seriously rusted and leave a loose fit on the new bleeder screw….you must go to method # 2 and install an oversized bleeder screw.
• Using either a caliper or drill bits, measure the bore size in the broken bleeder screw. Select a bit about .020” larger in diameter than the bore.
NOTE: this is best done on a drill press but can be done with a hand drill at low speed.
• You want to drill only deep enough to reach through the end of the threads so mark your drill bit with tape. You only want to relieve stress to the end of the threads. If you drill through the bleeder at the bottom you will ruin the caliper.
NOTE: the bleeder screws are mounted at an angle so check your drill angles accordingly
• Drill out the core of the bleeder screw to the first oversize. In this case these particular bleeder screws used drill bits of 0.144” and 0.167”. Your may vary slightly…but stay inside the major circle of 7mm x 1.9 threads.
• Select a drill bit approximately .020” larger and repeat.
These sections show what we are working for. You want to thin the walls of the screw to make them more flexible and relieve stress on the rusted threads from the inside.
• With a propane torch or similar, heat the bleeder screw to about 300°F to 400°F. This only takes 3-4 minutes.
• While it is hot, strike the top end of the bleeder screw several times with a flat faced punch and hammer. Just enough to set up vibrations.
WARNING NOTE: Wear safety glasses, gloves and respirator for this next step.
• With a medicine dropper or a straw with your finger over the top, drip several drops of Muriatic acid onto the bleeder screw. After the acid flashes to smoke and cools slightly. Repeat several times.
What is this step doing?
The heat causes the metals to expand. It causes fissures in the rust in the threads. The muriatic acid does two things:
1. The acid rapidly cools the metal causing shrinkage and fracturing of the rust. As the metal cools, it pulls liquid into the fissures
2. Muriatic acid totally dissolves rust to nothing. Every spec of rust the acid can reach will dissolve. As the rust dissolves it exposes more rust underneath to be dissolved.
3. Repeat this several times letting the acid work for about 5 minutes each time.
• After rinsing with water, blow dry and apply more heat and then penetrating oil.
• Now use an easy out that is barely oversized to remove the bleeder screw.
Caution: if you use too large/tight of an easy out you can damage the threads in the caliper casting. Remember that after drilling the wall of the bleeder screw is thin.
If you have repeated the acid treatment enough….the bleeder screw will always come out easily.
2. Drilling oversize and re-threading bleeder screws to 8mm x 1.25:
NOTE: This same drilling depth should be used when drilling for the oversized 8mm x 1.25 bleeder screw.
This is simpler but has risks. You MUST be sure your drill bit is centered and at the correct angle (see angle pictures in earlier section). I fully recommend a drill press and vise.
• Use the two step drill method as above to widen the hole in the bleeder valve.
• When the second oversize bit is drilled, install it in the drill press chuck. Use this as a guide in the hole in the bleeder screw to align and mount the caliper securely in the vise on the drill press so that the angle is correct.
• Remove the drill from the chuck and install the 6.7 drill bit for 8mm x 1.25 in the chuck. Now the angle is correct.
• Mark the bit with tape to only drill as deep as the existing threads on the bleeder screw. When the bit cuts through the last thread, the unthreaded tip of the bleeder screw will be freed.
• If necessary, drip acid into the bore to derust the bleeder screw tip.
• Start the 8mm tap to get out threads started.
• Once starter threads are started on all broken bleeder holes, grind away all but one tapered thread from the end of the tap so you can bottom the threads at the right depth.
• The proper oversized Speed bleeder part # is SB 8100
Bleeder screw types/differences:
Note that the stock bleeder screw is long. This is what makes it unique from many other bleeder screws. It needs to be taller so you have wrench access. It also has a longer wrench access area which nice.
The Speed Bleeder is just long enough. The Dorman screw will just work (if it has no tip angle issues) but will be very difficult to open and close on the counter bored bleeder screw area of each caliper. Note the blunt tip on the Dorman screw. These particulars screws do not seal. I am not sure if this a is a production issue or a specification issue.
This is the Dorman 13905
This is the VW 311 615 273
This is the Speed Bleeder SN 7100
DO NOT USE THESE BLEEDER SCREWS!
Casting Inspection and bore cleaning:
NOTE: some of the following pictures are done before major cleaning and some after so follow directions and not so much the picture sequence. The pictures are for instructional reference.
This is the outer caliper casting condition after solvent cleaning, scrubbing and acid washing and has no oil on it. There should be “0” paint, crusty rust or brake dust grime anywhere on the calipers. The flash rust is not an issue and is actually a benefit as these will be converted with phosphoric acid before painting.
If you do not plan to use phosphoric acid, your calipers should be oiled immediately after coming out of the degreasing and drying.
This is why we want to ALWAYS replace the caliper half mating seals.
Top half port
Bottom half port
These pictures were taken immediately after splitting this caliper. Notice that even on matched caliper halves the alignment of the fluid orifice is not perfect.
With age the fluid flow erodes the inner bore edge of the seals and they do not last forever because this erosion opens the edge of the rubber to attack. They last a long time…but not forever. Heat has a lot to do with this as well.
Also notice the corrosion staining that is infiltrating the machined surface from the inside edge. You need to split the calipers to clean, replace seals and correct/preserve the mating surface every so often.
When its time to rebuild a caliper for any reason, even just a split out boot....its time to replace ALL the seals. They are the same age and made of the same rubber.
This is a picture of the same fluid port as above (the bottom half port) of the same caliper about 12 hours after splitting the calipers. You will note that the caliper mating surface has been smoothed of corrosion, the bolt holes have been re-tapped to 8mm…and MOST IMPORTANTLY…you will notice that the original seal has shrunk in both diameter and thickness. THIS IS WHY WE REPLACE THE CALIPER HALF SEALS.
This is caused by degradation to the EPDM rubber due to time, heat and chemical attack. When you expose this to oxygen and uncompress it from between the caliper halves…it will shrink.
If your calipers have sat idle for any period of time with air and moisture in the system, this can happen even if you do not split the calipers…which is why many old calipers start to leak.
This is the same port with a new seal.
After about one week out of the caliper. The original/old seal is on the left and the new one is on the right. Folding the seal cracked it …showing just how hard and brittle it is. REPLACE THESE SEALS!
Bore and piston inspection:
An example of one of my caliper bores:
Specification: 42mm (1.653”)
Actual after acid wash: 42.037mm (1.655). This is .002” oversized from spec.
Piston (with plating still on): 41.960mm (1.652”)
Tolerance: 0.003” with slight variation vertically in the cylinder.
NOTE: all the bores were slightly different but similar with the same level of tolerance so there is some production variation.
Piston after de-plating and polish: 41.935mm (1.651”)
NOTE: this brought the final tolerance to .004” at the upper half of the bore closer to the sealing ring to .0045” down near the base of the bore where the most rust was. Still well within specification.
Drawing a fresh razor blade across the mating surface at a high angle…scraping fashion….will reveal any burrs or high spots. This side of the mating surface always seems to have higher machine marks
The fluid ports and mating surfaces all look like this.
In these two you notice that there is almost as much pit surface area as high point surface area. These area with a disc micrometer read almost factory specification for diameter. After lapping they will have no bearing on the piston other than a guide for the piston …which is all the cylinder is. These are perfectly acceptable.
A little more global view of this cylinder. You can see how much light area…undisturbed wall there is for cylinder guidance. It will work perfectly once lapped. This cylinder is chosen even though it was the worst…its indicative of the condition of most cylinders.
The tolerances are good enough that I would not even try to get rid of most of these pits. They just do not matter. Notice how clean the seal groove is. No intersecting pits.
This is indicative of the condition of all of the pistons
This is the typical condition of most of the pistons. This is before removing the plating and most of the rust with acid. Notice the red arrows. You can see where I ground away the thin outer boot flange (red arrow). It was chipped, cracked, jagged and sharp and would have cut the new boot installing it.
Just grind it smooth wherever it’s chipped. The two red rings are showing gouges in the plating. They are very shallow in the .0015”-.002” deep range. They ran 60,000 miles with no leaks. They will be half that depth when I remove the plating so they are of no concern.
Another view. It may be the same piston but the other side. The two red circles show deep pits of .005”-.007” but neither are as wide or wider than the seal so they do not matter…and again they drove 60k miles with no issues and will be about .0015” shallower once I remove the plating. The green ring is very shallow scratch less than .001”
Acid washing pistons to remove chipped plating:
Generally acid does not easily affect smooth, unchipped chrome plate. However it affects the base metal that is plated to the steel that the chrome layer is plated to. It eats the intermediate layer.
When you soak these pitons in muriatic acid, you will notice a slow, fuzzy, and hard to see “whitish” fuzz growing on the surface. If you look closely you will notice this as being foam or tiny gas bubbles. As it progresses you will see a gray residue form in the bottom of the dish.
This is the chrome.
About 10-15 minutes in the acid will produce a uniform matt gray finish on the pistons. This is the original textured steel that was plated. It is very fine texture.
Notice as compared to the previous pictures that the acid did quite a nice job of removing the crusty rust inside of the piston. The blackish residue in the lower picture is just a bit of thin rust in a heavily rusted section that was treated with phosphoric acid.
Polishing de-chromed Pistons:
Buy a 1” diameter by 0.75” long rubber expansion plug at the hardware store (about $1.25). You may need to grind the rim of the lower washer to make sure it fits inside the piston. With no tension on the bolt you may need to simple rough trim with a razor blade to make sure the rubber bung is a snug fit in the piston core. Tighten the nut.
Chuck the bolt into either a drill press or a hand drill that is clamped to the workbench. Keep speeds moderate (about 500-900 rpm).
About 800 grit paper is as rough as you want to go. Start polishing with 800-1000 grit for maybe 20-30 seconds just to knock the peaks off the very fine texture. We are not trying to remove metal at all. Then stay with 2000 and maybe even 3000 grit. We are only trying to polish very smooth.
Cut the paper strip wider than the piston is long by about 3/8”. Keep it uniform in tension and move it up and down a little. About 2-3 minutes or enough to make it smooth and shiny is all it requires.
IMPORTANT NOTE: you will note that this piston already has the outer boot installed. This boot was already adhered because this piston was already finished. It was just used to make the picture for this illustration. You should have no boot attached when you do this polishing. The piston will need to be solvent washed when you are done polishing.
This is the polished piston. The “visual” texture you see are the original grind marks from when the steel piston was made. The polishing has left it far smoother than the visual looks. The surface profile just for reference has been checked (because I have the tools to do so) and is within about 2% of what the original chrome plate was. This is plenty smooth for the sealing ring.
MODIFICTION: Replacing 7mm cap screws with 8mm X 1.25
The original 7mm bolts were a little spindly and snapped easily with age and rust. I will never know why ATE chose to use odd 7mm bolts when there is plenty of metal and even large enough bolt head reliefs to use 8mm x 1.26 bolts. Also the early models of type 3 and 4 with the 8mm Allen head bolts are absolutely the worst for stripping the socket trying to remove rusted bolts.
A hex head cap screw is ideal. Use anti-seize compound and a 12 point socket and it will never have issues.
You will also notice the original drilling relief on the threaded half of the caliper. It is also possible that ATE built these with 7mm knowing that it would make the “second life” easier on remanufactured units to just center drill, tap and install 8mm bolts….speculation if you please.
• The original bolt holes were only threaded on one half of the caliper. The unthreaded bore holes in the other caliper half and for a few millimeters of the other caliper half are almost exactly 6.7mm which is the drill bit size for the 8mm x 1.25 tap.
This is the 6.7mm bit compared to the unthreaded hole. Nice fit.
• The unthreaded caliper half is the drill guide for the drill bit to keep it centered.
• To make sure these holes are drilled and tapped perfectly straight, the caliper must be properly assembled and torqued tight.
• Because the new holes will be threaded all the way through, if the two caliper halves are not held tight with no movement until all four bolt holes are drilled oversized and threaded, there is a slight risk of binding because of thread misalignment.
• One bolt at a time will be removed, drilled and tapped.
• The new 8mm x 1.25 bolt will be installed and torqued
• Move to the next bolt.
• You should maintain the proper torque sequence when tightening, removing and drilling/tapping the bolts.
These are what we are putting in. They were bought 10mm long so they have to be cut to length. You can use split lock washers but I think the ribbed Bellville Schnoor type work better.
Caliper halves torqued together and held securely in the padded vise.
#1 bolt removed
#1 bolt hole drilled with 6.7mm bit
#1 bolt hole tapped for 8mm x 1.25
#1 8mm x 1.25 bolt inserted and torqued
This process in proper torque sequence needs to be repeated for the remaining three bolts.
NOTE: The bolts you bought are oversized in length. Make sure you mark each bolt and trim the length to clear stop short of exiting the thread bore by ½ thread. This prevents rust from forming on the bolt and damaging the internal threads if you must rebuild again later.
Cylinder bore lapping:
The bores should be generally de-rusted already by now. Either from using a wire brush by hand to remove crusty rust or by acid wash to remove all but the thinnest films of rust in the pits.
NOTE: do not use phosphoric acid treatment in the cylinder bore. Some light over-splash is fine but rinse it away. Most phosphoric acid treatments contain a protective polymer.
While it will not generally hurt anything under paint, it can be flaked off in the cylinder bore and get between the seal and the piston and is not necessary in the cylinder bore.
Unlike with the piston, “smooth enough” is the name of the game here. The cylinder bore is only a guide for the piston. Much like a master cylinder bore it generally does not have much contact with the piston.
Grossly oversized bores are a risk to over-extension, over
expansion and distortion of the piston seal ring so we are not removing any metal here. We are only smoothing the cylinder walls so that the very bottom edge of the piston which can cock slightly and drag the cylinder wall.…has negligible friction.
Use a 41mm/ 1”-5/8” hole saw to cut a plug out of a piece of 2” x 4” wood
Here is the plug with a nice centered hole from the saw
Place three marks 120° apart
Make a 3/8” deep vertical slot with a hacksaw or coping saw at each 120° line.
Then make shallow horizontal cuts on each line to remove a wedge and make a “shelf”
Take a 6” long piece of threaded rod the same diameter as the drill bit in the hole saw and make a centered shallow point on the end. I did this with a file in 30 seconds by chucking it into a hand drill.
I made a recess in the end of the plug with a Dremel tool and a routing bit
The recess only needs to be deep enough to hide the nut and washer so that only enough of the point protrudes to guide off of the machine center recess in the caliper bore.
Start with 800 grit as the roughest and work up to 2000 grit
Depending on the thickness of the sandpaper, you can get away with three short and three long strips. Cut with care so they are straight and even.
Stack them upside down and then staple them to the ledges of the plug. The ledges are there to prevent the staples from contacting the cylinder wall.
NOTE: you may need another layer of sandpaper (no one strips total in three lengths so they underlap each other)
fold the paper backward so that the abrasive is exposed.
Voila! Lapping tool
NOTE: make sure the fit in the bore is snug but no so tight that it tears/crumples the brasive paper. If you have only one direction on your drill, mind the direction when you make the “shelf” slots on your tool.
Surfacing the bores only requires about 1 minute at 300-400 rpm with a little household oil.
When this bore surfaces are complete, a complete solvent wash with first general solvent and bore brushes in all holes, then followed by soap and hot water, then dry and use a hot, no residue, fast evaporating solvent (MEK, acetone carb cleaner etc.).
Phosphoric acid Treatment:
NOTE: read the directions on the container! Reassemble the calipers with no seals…temporarily…to keep phosphoric acid off the mating surfaces as much as possible.
• Wear gloves not only for protection but to keep oils off the surface of the caliper castings.
• Brush phosphoric acid liberally over the complete caliper. Avoid the piston bores.
• When the coating is complete, blow off excess with very low air pressure to get rid of any foam and bubbles and to leave the coat as thin and uniform as possible.
• LET THIS DRY FOR AT LEAST 8 HOURS UNTIL IT IS COMPLETELY DRY. It needs reaction time and must be completely dry.
• Repeat if necessary.
This picture is of the caliper masked for paint but shows the surface color and texture after phosphoric acid treatment and ready for paint.
WEAR A RESPIRATOR, GLOVES AND SAFETY GLASSES!
Lots of opinions on this. Some want powder coating. In that case, work with your powder coating agent for pre-treatment. Most of the pre-treatment in this document may not apply to you.
You can use any high temperature paint you desire. It should be good for at least 450°F sustained and 600°-800°F Peak temperatures.
NOTE: I have had good results with the VHT high temperature caliper paint. I like it because it applies like epoxy and flows out well, looks good and holds up well. BUT…it must be baked.
Many people get away with it hoping that basic brake temperature completes the curing. However I have found that until it is pre-baked, any contact with brake fluid will remove the paint.
You may destroy your paint job during the first bleeding of the system if you do not cure the paint.
The two best masking tapes I have found are the #M blue painters tape and even better “Frog Tape” green painters tape (Home depot, Lowes, most hardware stores). I find it is better than 3M blue.
You want to loosely but carefully mask the cylinder bores, make a small circle to cover the fluid inlet hole (or use bolts or old brake line fittings) and make a tight flat seal on the mating surfaces and then trim with a fresh, sharp Exacto or razor blade around the edges of the mating areas.
NOTE: install old, clean bleeder screws into the bleeder valve holes during painting to keep paint out of the threads and ports.
NOTE: Spend $7 on one of these. It gives much more professional results and control http://www.lowes.com/pd/Rust-Oleum-Comfort-Grip-Un...4e4d5a73a3
Space the caliper parts out so you can work around all of the edges and not mix up the parts from each caliper. Paint one side at a time. Let dry with VHT for best adhesion from coat to coat.
Then flip them over. Note the blue tape spots to cover the fluid line port. You can also use old brake hard lines and connectors or a bolt that fits.
You want to get the second half coat applied within a few hours so the paint layers bond. If it’s cold an drying slow, use a warm air heater.
This is also the time to clean and paint all of the bolt heads silver by mounting them in holes in a piece of cardboard. Do the caliper mounting bolts if you so desire.
Baking Caliper paint:
I have a small Oster brand stainless steel combination convection oven/ broiler that I bought at Wal Mart. I actually have two. It is a superb toaster oven for cooking all kinds of things. I have one for cooking and one for working with industrial and car projects. Best $99 I have ever spent. Both times…for cooking and for work! http://www.walmart.com/ip/13729291?wmlspartner=wlp...mp;veh=sem
The plate inside is a piece of $2 ceramic floor tile from any home improvement store.
You can see I have one caliper half inside, along with the painted bolts for assembly and for mounting. Use blocks of metal to keep the bolt heads off the plate so the paint does not flow and stick.
NOTE: ignore the temperatures you see advertized in other forums for the VHT product.
Here is what VHT says: http://www.vhtpaint.com/high-heat/vht-caliper-paint
I have found good results with this: Set the oven for 250°F and bake for about 2 hours. Then let it cool completely.
You can use peaks of 325* F for a while but it causes paint to flow a bit and masking tapes to fail.
CAUTION: DO NOT bake calipers for long periods above 250*F...pre-assembled with seals inside.
Here is a chart of elastomer temperature ranges. EPDM can hit very high short temperature peaks many times over its life span with no real issues...but that is also with plenty of brake fluid running through and around it to transfer heat....not high sustained heat with no heat transfer fluid.
This is the complete kit without the caliper half rings in this picture. This was a Centric branded kit from Rockauto. They turned out to be top quality FAG parts.
Here is a whole caliper, cooled out of the oven and ready to assemble.
Remove all masking.
Around all mating areas, carefully scrape lightly with an Exacto or razor blade at a 45° angle to trim away any paint film that was attached to the tape.
CAREFULLY with cotton swaps and small sections of paper towel DAMP with a hot, fast drying solvent (acetone, MEK, Carburetor cleaner) wipe the cylinder bores, pistons and mating surfaces, concentrating on the seal ledge inside the cylinder. Make sure that all leaked paint overspray is removed and wipe until the paper towel comes away clean. Stay off the paint.
Because I trimmed away the cracked boot retainer ledges on my pistons, run a thin bead of high temperature RTV (Permatex Ultra series of similar capable of 600°F).
Install the booty, twist ¼ turn to distribute sealant. Wipe away any excess. Let dry. This also helps the boot seal even if you have perfect pistons and makes it easier to install later.
With a cotton swab or cheap eye-shadow/makeup applicator, apply cylinder assembly paste to the seal grove and in a complete by thin coating to the inside of each cylinder.
Apply to the sealing ring
Install sealing ring in bore.
Install the anti-rotation plate. Make sure of your plate orientation (check the book). They are different for leading and trailing calipers.
Use the anti-rotation plate as a guide with the retaining pin hole to make sure the piston is oriented. Press the piston into the bore until it seats.
Use your thumbs to seat the boot snap ring. Also I use a piece of wood dowel and a rubber mallet. It may displace a small amount of paint on the rim until it seats.
Repeat for the other caliper half.
Make one last solvent cleaning wipe of the mating surfaces.
Install the new caliper half seals DRY.
Mount the caliper half in a clamp or padded vise so that the seals do not fall out and screw in all four bolts finger tight. Use new Schnoor lock washers. Mind the bolt length. The two inner bolts are longer.
Make sure you follow the torque sequence. I torque to 10 Ft. lbs. first pass.
The listing is only for 7mm socket head bolts and 9mm hex head bolts. I have found that 19-21 ft. lbs. for 8mm X 1.25 works excellently.
As mentioned earlier there are some good hardware kits out there for cheap.
These are from RockAuto and are Centric branded but appear in Every way to be re-bagged Wagner parts.
There will be additions to this document later.
Joined: November 24, 2008
Location: Des moines Iowa
|Posted: Thu Jun 30, 2016 11:24 am Post subject: Re: Type 3 and 4 front caliper rebuild "how-to" part 1 and 2
So….I have already gotten a couple of questions of e-mail…primarily from people I know on other sites that were also working on their brakes.
1. Why do I believe it’s good enough or good practice to simply remove the surface rust and lightly smooth/improve the surface texture of the caliper cylinder bores……when many other people, sites and even rebuilding businesses say the bores should be honed?
A. In the first place….I do hone them. Honing…depending on who is doing it and why…. is not “generally” a material removal process. It can be….but in this case it is for removing loose surface rust …which “blooms” outward bridging the gap between cylinder wall and piston and knocking the sharp peaks off of the metal that were created by the rust blooms.
The gap or tolerance between piston and bore in calipers…while it may seem pretty relaxed…is actually pretty sensitive once it gets over a certain number.
B. Honing or grinding down to a perfectly clean level of the cylinder wall…meaning no pits and no peaks over a handful of microns high….is totally unnecessary in a caliper cylinder…unlike an engine cylinder.
The piston does not seal against the cylinder wall. The cylinder seal is stationary and the piston moves through the seal. This is also why having “cross hatch” pattern in the cylinders is totally unnecessary.
C. Honing, whether you use a rigid expandable stone set like you would for an engine, or use a brush hone (one of the best tools if you use it right) or a commercial made or homemade lapping tool like I do….all work just fine. Use whichever you are most comfortable with.
However…honing down to smooth, “fresh metal”…..not only increases cylinder to piston tolerance which is bad…it sharpens the fine bevel at the edge of the sealing ring recess. The sealing ring recess is THE MOST critical part of the cylinder.
NOTE: if you must use any type of stone or brush hone in these cylinders……keep the grit as fine as possible and leave the old seal in the grove in the bore while you hone.
This keeps brush hones from getting into the sealing groove and doing excessive wear to edges and dimensions and keeps stone type hones from sharpening the upper and lower edges of the hones. When you are actually done cleaning the cylinder with a brush type hone…..it’s excellent habit to then pull the old sealing ring out and give just a limited slow speed run through with the brush hone so that you “clean”…but do not change….the sealing ring groove.
2. Why is slight oversizing or making sharp edges on the sealing ring groove during honing an issue?
A. to be precise it’s only the upper/outer edge of the sealing groove that is most critical not to be sharp. During operation….the sealing ring is forced against that edge and is slightly extruded. It is the action that makes the piston retract a measured amount when you let off the brake. When the upper seal groove edge is sharp…it can cut or abrade into the seal over time.
B. For the same reason above….grossly oversized can mean anything over .005” depending on your brake pressures. Excessive tolerance will extrude too much of the seal out of the seal groove, literally wrapping it around the upper edge of the seal groove.
In extreme cases…more common than you think…..with age and heat…if enough of the seal extrudes into the bore space between the piston and cylinder and it cannot retract back into the seal groove when hydraulic pressure is removed because it gets hung up on the rough or sharp upper/outer seal groove edge…..it lodges between piston and cylinder. The does not allow the piston to retract and you get a “hung” piston and brakes that can stay locked or partially locked.
3. How these caliper pistons actually work:
This shows the caliper at rest. No pressure. The piston has allowed the pad to retract to the engineered gap between pad and rotor called “Windage” or venting thickness. In reality the venting thickness is the level of flex in the rubber piston seal….which may be quite large…but the resulting gap between pad and rotor may be as small .00005” or as much as .001”.
There are many statements on the internet from people who say that disc brakes do not retract…they just drop pressure to ambient and that brakes drag all the time….and they have no idea what they are talking about. They are simply saying they observe something …the pad to rotor dragging…..so that must explain everything.
For instance on the rear calipers of a Porsche 914, the initial “Windage” setting or gap is .002”-.008”. This tolerance is setting. Once you actuate the brakes, this tolerance is cut down to under about .001”….but there is a gap. There is piston retraction.
The rubbing sound from the brake pads is the “peaks” of the micro texture of both the metals in the rotor surface and the material of the pad….touching. If you drive long enough without touching the brakes and then can stop the car without using them, jack it up and spin the wheel..…you will find this minor friction and dragging noise has worn away.
This touching together of two surface textures…is measured in microns at largest and micro inches at the smallest. Hit the brakes and heat, expansion and abrasion make new texture to start this process over again.
This is what the seals look like when you apply brake pressure. They operate….similar to the compression rings on an engine piston. They do NOT seal to the piston by SPRING or ELASTIC force.
On an engine piston, the top of the piston compression ring is canted inward in the groove. The gas pressure from above invades the ring groove and wedges the ring outward creating pressure against the cylinder wall.
On the caliper piston….the ring grooves in the caliper casting (on some) are subtly canted. In all….the rubber ring deflects concave on the lower horizontal surface of the sealing ring FIRST from hydraulic pressure. This allows fluid pressure to distort the ring…AND…invade the space behind the ring…distorting it inward.
This creates great sealing pressure on the piston as well as forcing the ring to flex upward along with the piston movement.
It also simultaneously forces the sealing ring up HARD against the roof of the sealing ring groove so that the fluid cannot bypass all the way around the seal…so it does not leak.
NOTE: When you let off of pressure….the seal retracts to normal. Also the anti-Rattle spring has wedge shaped spring sections that aid in pushing the pads away from the rotor very slightly.
Here is a detail of what is happening to the seal under pressure.
Here is what can happen to the seal when the piston to cylinder tolerance is excessive.
4. How can the homemade lapping tool work on the early 411/type calipers with the guide pin in the cylinder?
Blues90 actually asked this question in the type 3 forum. These earlier calipers are actually why I made a homemade lapping tool because otherwise I had always CAREFULLY used a honing brush like this one from Brush Research.
For the early 411 and type 3 calipers with the anti-rotor flex pin inside…..simply use two “plugs” of wood cut with a hole saw from a wooden 2” x 4” and connect them together like this.
Joined: April 20, 2004
|Posted: Thu Jul 07, 2016 2:33 pm Post subject: Re: Type 3 and 4 front caliper rebuild "how-to" part 1 and 2
|This is fantastic.
Follow-up question: I see that the 914 half seals will work for later T3s. Will they work for early (66-6 T3 discs, too?
Thanks for posting this thread!
Joined: November 24, 2008
Location: Des moines Iowa
|Posted: Thu Jul 07, 2016 2:38 pm Post subject: Re: Type 3 and 4 front caliper rebuild "how-to" part 1 and 2
|coach macinnis wrote:
| This is fantastic.
Follow-up question: I see that the 914 half seals will work for later T3s. Will they work for early (66-6 T3 discs, too?
Thanks for posting this thread!
That...I don't know. Ray
Joined: February 06, 2013
|Posted: Sat Nov 19, 2016 5:12 pm Post subject: Re: Type 3 and 4 front caliper rebuild "how-to" part 1 and 2
|thank you for putting up this post . I have spent the last five days rebuilding my front calipers , after work a little each day . I also looked for info on the samba each day as i encountered the need to . I stumbled upon this gem today with a search from the home page entitled " Are the caliper piston seals tapered? " I haven't had this query answered , I think new ones are probably square ( mine haven't arrived yet ) but the old ones do show a small taper on the outer diameter . Great write up and though I am not going to such great detail on my rebuild I feel I am at least on the right track with a guide to follow . Thanks again Samba
Joined: November 24, 2008
Location: Des moines Iowa
|Posted: Sat Nov 19, 2016 7:23 pm Post subject: Re: Type 3 and 4 front caliper rebuild "how-to" part 1 and 2
| thank you for putting up this post . I have spent the last five days rebuilding my front calipers , after work a little each day . I also looked for info on the samba each day as i encountered the need to . I stumbled upon this gem today with a search from the home page entitled " Are the caliper piston seals tapered? " I haven't had this query answered , I think new ones are probably square ( mine haven't arrived yet ) but the old ones do show a small taper on the outer diameter . Great write up and though I am not going to such great detail on my rebuild I feel I am at least on the right track with a guide to follow . Thanks again Samba
Thank you! No the caliper main bore seals are not tapered. They are square. As i noted in the diagrams....just a few thousandths of piston movement when you lush the pedal....stretch them out enough that the surface area is high enough in the face of hydraulic pressure....that they are squeezed. When you squeeze a cross section of rubber....it does not compress into a smaller space....much. Its too dense for that.
It displaces.....meaning you squeeze rubber in one direction...it expands in another. In this case hydraulic pressure squeezes the flat lower edge of the seal. It expands sideways.....sealing the griove in the piston wall....and squeezing the piston harder.
I have jot measured...but from things I have read.....I "think" the seal groive may also be canted slightly. Ray
Joined: January 01, 2017
Location: Stockholm, SWE
|Posted: Thu Jul 20, 2017 1:14 am Post subject: Re: Type 3 and 4 front caliper rebuild "how-to" part 1 and 2
|superbly detailed write up!
Joined: May 10, 2013
Location: Sydney Australia
|Posted: Tue Aug 07, 2018 9:48 pm Post subject: Re: Type 3 and 4 front caliper rebuild "how-to" part 1 and 2
|I'm trying to source the caliper half o rings for a SINGLE pin ATE disc brake here in Australia.
Do you remember the seal size? I can use your original link to get the two pin o ring, but do not know if it fits the single.
My measurements show the OD of the caliper orifice to be about 10.8mm and ID 6.0mm
Joined: November 24, 2008
Location: Des moines Iowa
|Posted: Wed Aug 08, 2018 8:09 pm Post subject: Re: Type 3 and 4 front caliper rebuild "how-to" part 1 and 2
I will post meaurements of the 914/411 and 412 caliper half o-rings in the am. Ray
Joined: May 10, 2013
Location: Sydney Australia
|Posted: Sat Aug 11, 2018 12:34 am Post subject: Re: Type 3 and 4 front caliper rebuild "how-to" part 1 and 2
|I measured the original o rings which admittedly have sat “relaxed” and out of the calipers for some time at 10.6 mm x 6.0mm x 2.3 mm if that helps.
They look in reasonable shape and not distorted like the ones you have in your excellent treatise above. But then again yours may have returned to a normal state if left long enough.