411-412 Brake hydraulic parts reconditioning techniques

[raygreenwood]

Ok...going to start this thread for a lot of reasons. I am making it a separate thread than these two which will be referenced here occasionally...


411-412 rear brake pressure regulator
http://www.thesamba.com/vw/forum/viewtopic.php?t=664753

and

Type 3 and 4 front caliper rebuild "how-to" part 1 and 2
http://www.thesamba.com/vw/forum/viewtopic.php?t=658176

...primarily because those two threads deal specifically with how those two parts can be reworked or how those parts work inside.

This thread is not going to be specifically about calipers or proportioning valves or master cylinders...but all of our brake hydraulic parts in general and techniques and problems in restoring and rebuilding them.

The why…of why I am starting this thread is because of several reasons

1. Outside of our front calipers (which are not getting any more plentiful for original rebuildable cores)…..parts like our master cylinders and the rear proportioning valve are already quite rare.

2. Because of the rarity of cores for the parts I listed…..when you find them…they are either nearly shot and need serious real work…not just a lapping and new seals.

3. Because of these issues……brake hydraulic parts is going to be one of the serious impediments to driving these cars. Not just restoring to say you have it period correct….but the actual ability to still drive them safely. The lack of brake parts is one of the key items that can keep you from ever driving your car again…if you cannot get what you need or fabricate something to replace it.

4. I am not that old….53…and am in good shape….but by the time this car is really done and on the road it will probably one of my last builds. I do not plan to have to rebuild totally every 3-4 years…and suffer the issue of finding cores again. This will only get worse.

For these reasons….I think that if we can…we should start to get serious about real factory level rebuilds of our hydraulic brake and clutch parts.

My project for adding the type 3 master cylinder in the trunk to move the MC out from under the dash….is a great and worthy project. Not that hard…but time consuming…and too many sub projects like that…may just keep this car off the road.

I am actually weighing the time and cost…of simply having one of my stock MC’s…stainless steel sleeved and replated…and then installing a drip tray underneath in case it leaks or for when it has to come out….versus the trunk mounted modification and all the fabbing for that.
The master cylinder would largely last forever if done like that.

While my caliper "how to" touched on more than a few issues regarding rust and plating....a must read....very good read is this article right here.

http://www.pmbperformance.com/brakehowto.html

While their "caliper how to" article...is not as long and detailed as mine..... ..... PMB Performance are the absolute experts in the Porsche brake rebuild industry ...whom I did not even know existed a year ago....for some insanely odd reason I had not come across them in my searches.

If you can afford the quite reasonable rebuild cost price for front calipers or the rear brake proportioning valve...you cannot go wrong for reasons I will get into shortly.

Compared to PMB’s knowledge and experience….I stand by my caliper rebuild document in all respects…except two.

1. PMB Performance are correct that for best 100,000 mile plus reliability…the caliper castings should be re-plated with zinc…even if you plan to paint them. If you do not do this….then for sure you need to be bleeding your brakes every 1.5 years maximum and tearing these down about every three years to check for rust in the bores….and I agree with this. So outside of that my rebuilt calipers will work like factory….but just require more maintenance.

2. The pistons should be re-plated…..and I agree so much….that I really hated the fact that in my rebuilds I stripped the pistons. They really need to be plated…..so I will be tearing down my beautiful rebuilt calipers…again….and plating the pistons.

More items that they…PMB Performance….. note that are part of the gist of this thread...are the brake building "MYTHS" they bust.... hallelujah!! …I have been harping on these myths for years!!!!

1. All calipers and brake hydraulic cylinders come zinc or cad plated from the factory. Yes.

2. The myth that you should never, never split the calipers…is absolute bullshit. You should never NOT split the calipers and replace the caliper half seals.

3. The anal issues about the 20* piston cocking tool for the shim cutouts.
Seriously…read that article from PMB and peruse their site. Really excellent stuff.

4. You do NOT ever...hone caliper or cylinder bores....as I have been saying forever. All factory new bores are smooth as glass...because they are plated. The smoother the starting bore when plating...the smoother the plating. At the most..they are lapped smooth...and then cleaned and plated....buffed and then plated again...and left that way.

So....after the thread about the brake proportioning unit…and there is more to come on that as I have a viable core coming next week…..and after tearing down the two cores I have….which have bore rust damage….I realize now that the proportioning unit will never be truly a good working unit that will live long….without being re-plated.

The smart/easy thing to do would be to ship the proportioning valve to PMB Performance and have it rebuilt which includes plating…for $169.
However….this will not get my pistons re-plated in my calipers….as they would probably want to just sell me their completed calipers …but $300 (while fair for new plating and everything) is just too much for me. And will likely not do anything for any of my other plating needs.

So….I am getting into the position to do limited zinc plating for my parts…with a chromate top coat…and electroless nickel plate (e-nickel) for the piston.

My proportioning valve cores:

So I have two cores with caps and brackets but no usable pistons.

I started cleaning the cores. One is much worse than the other.
It’s double hard on these parts. They are down underneath in the road salt and slush and in an out of the way place so they never get washed. They are moisture traps inside and rarely get a good flushing during brake bleeding.

To add to that…once the inner seal craps out….it floods the spring cavity with brake fluid….so once these get crusty…they need real work.

This was just to start and see if I even had a usable inner bore on any of the castings. The one on the left in the pictures was the worst.

Sorry the bore pictures below are so bad…but this is after acid washing and neutralization to remove rust. I am having problems with the right angle attachment for my microscope so this is the best I could get at the moment.

This is the cylinder body on the right and can probably be lapped to work….but will be re-plated anyway for longevity.
Again sorry for the poor pictures….this is with a USB microscope. Its depth of field is very short at these distances so I am looking at one specific focal point which is the lines in the lower 14mm bore.

This is the bore on the left. Lots of damage. This one will need to be lapped slightly oversized and then re-plated back to normal size.

I have a complete core from a 914 with a piston set coming in a week. I will tear that one down. Get started on the plating and buffing and then do a rebuild with a PMB kit.

More to come…..but I also want people to talk about restoration techniques in thread for calipers, wheel cylinders and master cylinders…and not just re-assembly and new seal kits.
Those are for other dedicated threads about those parts.

This thread is for restoration and preservation techniques like plating, paints etc for these parts.

Ray

[raygreenwood]

Some material to add....food for thought...nothing that is super pressing:

Master cylinder bore sleeving:

So I go through this cycle about every 2-3 years...with regard to my brake parts choices.

1. The first thought is to just find a stash of good NOS master cylinder cores and rebuild with new seals from a type 3 kit...pickle the spare cores in ATF fluid. In this way I have new factory level cylinders so I...ME....can always have brakes on my car.

Of course this does not do anything for anyone else in the community.

I would tear mine down every two years, inspect and bleed and put in $25 worth of new seals and motor on into the sunset.

Then...reality sets back in...and I notice that what I find...when I find it...are NOS cylinders are truly ignorant prices. Typically $200.....and really its just a core. Or...."used" cylinders....listed as"good decent used"....and they are also for truly ignorant prices. They are just rusty cylinders and may not even be good for cores now.

2. So I move onto the train of thought of having my cylinders professionally rebuilt....which is an option going to someone like PMB. Cost is a factor....and even PMB (and there are others) ....will have nothing for pistons and seals.

3. So I move onto the train of thought of just having mine re-sleeved.

I have looked into this numerous times and I always walk away from it and move toward doing refurbishment myself. I always forget why I walk away with an odd feeling from the "sleeving" technology out there....and have to re-research it to remember.

So here are some options and some questions I have about them. These are just off the top of the Google list...but most of them are the usual suspects that I have checked in the past.

Cylinder sleeving companies:

http://www.applehydraulics.com/brakes.htm

This company has been around a long time. I have looked at them event 10 years ago. My issue is that they use Brass instead of stainless. This is a soft material and not especially corrosion proof in glycol based fluids. Of course if you treat it like you should...bleed every 2 years max interval it should be fine.

The issue is that if you get any grit in the outside area by the rubber boot...you can screw up the bore because it will groove easily.

http://www.karpspb.com/sleeving.htm

These guys are stainless steel sleeves. But...They use a method that calls for precision sleeve size in a precision bore...and uses a chemical "loc-tite" type of fixative instead of shrink fit or interference fit.

They also list that they hone for a cross hatch pattern. While they have extensive experience.....I know that NONE of the factory cylinders come with cross hatch. More on this.

http://southglenelg.com.au/our-services/brake-resleeving/

I put these guys in only for reference...they are in Australia.

These guys really seem to have it together. They make note that their stainless steel sleeves are pressed in...interference style....and that the fixative or loctite is only used as secondary insurance.

They also...if you are totally rebuilding in their shop..pressure test the cylinder to 2000 psi to test for leakage between sleeve and bore.

They also note that they believe in honing...but they do not say "cross hatch" honing. At some point I will contact them and ask them what they mean by honing.
Yes...I realize that you MUST hone...or at least lap the bore to get rid of the burrs from the compensation port and fluid holes that you will be re-drilling in the stainless sleeve. As they note in their "about sleeving" segment on their front page......you do not want the bore too smooth....or too rough.

Even factory bores...which are usually zinc or cad plated...are not "mirror" smooth. You need some tooth at a microscopic level to carry enough fluid between cup and bore to act as a lubricant.

But at the same time.....crosshatching is usually too rough. It really depends on what they mean.

https://www.brakecylindersleeving.com/

These guys use the same system as the one in Australia....the "Halray" bore sleeving system...interference fit and proprietary locking sealer. They again note cross-hatch honing...which bothers me.

yes...I have cross hatch honed cast-iron brake cylinders back in high school...and about 6 out of 10 times....they worked well. Those other 4 times....the cup edges wore out too quickly. Obviously the surface was too rough. Was it me?...was it the cups?.....

http://harmonclassicbrakes.com/brake-cylinder-sleeving/

Not too much info here.

http://www.brakecylinder.com/

Both Sadly and happily....Sierra specialties have closed because the RETIRED! Great to see someone will get to do that! But they are leaving the site up for historical. They would have been one of my better choices.

Just some things to look at for now. While sleeving with stainless would solve the issue....as long as the honing is good and closer to factory stock I think I would have no problems.

I am looking to probably zinc electroplate/yellow chromate the outside of the cylinders anyway...probably after sleeving.

This is also opening up some other thoughts. If I am going to get into plating....not just for brakes but for hardware as well.....I "could" just as easily plate the cylinder bore and be done with it.

Some thoughts about honing/lapping oversize:

Honing and bore specs:

Master cylinder bore size: 19.05mm/0.75"

Piston head size: 19.0mm to 19.01mm /.748" to .7485" (.748 is the most commonly measured size)

Allowable bore oversize tolerance: .004" between piston and bore as measured by a bore micrometer (best) or a precision gauge rod inserted between piston and bore.

So Bore ID of 19.11mm/0.752" is the extreme outer limit for honing/lapping.

This is also "part" of why rust pits of a depth more than about .002"-.003" make the bore un-rebuildable....partly because any deeper and the cups cannot seal...and any deeper and you cannot lap them out without making the bore excessively oversized.

I could plate/buff/plate and add about .0015" of zinc of zinc-tin to the inside of a maxed out bore and bring it back to normal tolerances.

Interestingly...and I will try this soon....I have quite a collection of type 4 master cylinder pistons that are in excellent shape...but have "white rust" or crust on them.
I was thinking these were zinc plated....as its obviously zinc corrosion....when I realized that they are actually solid zinc.

If I can chemically clean them just like before zinc plating a second layer (alkali cleaning)...and then lap the piston heads and flap valve areas..they may be perfect.

Ray

[titan3c]

Something I'm wondering about, is bench bleeding the master cylinder or bleeding the mc while installed. Bob

[raygreenwood]

[titan3c]

Don't want to get off the subject but I have another question. I'm going thru my brake system now, and notice that the brake fluid collected during bleeding is dirty looking not real bad, but not clear either. My assumption is to bleed until it clears. I have removed the regulator from the rear brakes, and have been working on the rear only. The dirty fluid is after installing a "T" to replace the regulator. I haven't bled front calipers yet. I'm thinking possibly the regulator could have dirtied up the fluid--haven't completed bleeding the rear yet. I'm replacing the cylinders, and haven't replaced the right one yet, but will tomorrow.

So what would the dirty fluid be a sign of, and of course it should be replaced. Bob

[raygreenwood]

[raygreenwood]

An update on parts that I am going to recondition:

This is a Porsche 914 rear brake pressure regulator I just got in the mail off of e-bay. It is identical in every way to the ones on the 411/412...except that it has only one fluid outlet port and uses a Tee to split the single outlet to the rear wheels.
I posted the differences here.

https://www.thesamba.com/vw/forum/viewtopic.php?t=664753

Now...on to what I found inside:

The pistons come out of these ugly....so the quotes from sellers about "good complete....should be functional"...are always 100% BS. I paid too much for this one but its was reasonable because I needed a core with a piston. This is what it looked like right out of the bore.
Remind the sellers of these that NONE of them are functional if they are either aged since the last rebuild at all...or have been open to the air at all.

Except that cores are getting rare...in my opinion...about $30-40 would be appropriate. This guy was asking a fair $45...I told him I would toss in $10 if he opened the cap to show me that at least the piston was still in the core...been there and went that route before...received an empty core...worthless.

This is where this part has bearing in this thread:

This part out of all of the brake system parts is the MOST susceptible to rust and corrosion...both from inside and outside. Its an absolute water trap on the inside of the upper and lower piston bore.

ATE plated the hell out of these to help this out. I am not fully sure whether it was just zinc with top chromate...or if cad plate may have been involved...but I suspect just zinc because of this....

This green goo in the cap...was not there when I cracked it open. The goo is made up of an emulsion of brake fluid, water and corrosion deposits.

It literally appeared in about 10 minutes...more on this in a minute...

Here is the cap with the goo removed and you can see where the plating was etched/eaten away.

You saw the dirty piston above...here it is clean(er). Note that the varnish on this piston....even MEK would not remove. Its going to take a light caustic soak.

Also note the erosion of the EPDM cup. The EPDM holds up very well to both acids and caustics....so I can only assume some product of either age or brake fluid break down made them dissolve this badly.

But...back to the green corrosion....

This green patina appeared in less than a minute in front of my eyes. There were similar spots of this inside the cylinder.

From doing some reading and research....this is zinc from the plating that was "white rust"...until I pulled cap off...and exposed it to air and moisture. It was fairly well sealed off from air and moisture in these areas of the piston and bore.

the zinc did its job and sacrificially corroded to white rust to prevent the bore from rusting. However when moisture gets to it with air...it quickly corrodes to a green. Some of this may have to do with the top chromate layer as well.

The upper 19mm bore and the lower 14mm bore were both in reasonable shape...only a couple of rust spots each...that corresponded to being directly in front of the inlet and outlet port openings.

So...the moral of this story...is if you want these parts to survive if you restore them....they REALLY need to be plated.

Its also clear that PMB Performance is correct that these units were plated all over even though they were then painted. This unit looked pretty good. About 90% of the external paint was intact. Where the brake fluid started to leak at the parting line gasket some of the paint was removed and you could see the zinc corrosion underneath starting.

Sorry...this is the eBay picture. I forgot to take one of the unit as it looked out of the box.

More as we get toward plating, painting and rebuilding of some of these parts. Ray

[raygreenwood]

A new installment:

So today we are going to take a look at some type 4 specific parts for some important identification differences for brake and clutch master cylinders as you are selecting and shopping for rebuildable cores.

As this thread moves along...since its mainly about reconditioning "TECHNIQUES"....although most of the parts you see will be type 4 specific....not all will be.

I will have separate threads when we actually get to the specific assembly of the brake and clutch master cylinders.

A couple of important warnings and notes.
PLEASE read these if you read nothing else.

1. I really do keep suggesting that you frequent RockAuto for deals on parts. If you are rebuilding your own cylinders and they are in good enough shape for a light lapping and cleaning of the pistons....you likely WILL NOT be able to find a type 4 specific kit with new pistons.

However...you can easily find VERY, VERY cheap kits for other VW and European based cars with the same seals, boots and flap valves.

Case in point: On Tuesday I bought two manufacturers closeout master cylinder kits from Rockauto...one for a 1975 Beetle...and one for a 1974 VW thing.....both were $8 each SCORE!

Both were EIS branded...which is a division of Standard Motor Products. Both were simply repackaged FAG/Shaffer kits. Both were probably 10-15 years old. Both had NAPA parts house box colors.

So....using all of the new seals, flap valves and boots with my old cleaned up pistons..I can rebuild one cylinder for $8 in parts and $5 in shipping.

2. BIG F*CKING WARNING!!

OK....one of these cheap kits....the one for the 1975 VW beetle...was perfect. The new pistons (which I cannot use anyway so they will be thrown away)...were nicely wrapped in anti-corrosion paper, the new seals were in a sealed bag, the new "C" ring, copper washer and zinc plated outer washer were in a sealed bag...all contained in an original but old, unopened box. Excellent!

However....the kit for the 1975 thing....has been previously opened and resealed with Rockauto tape.

Obviously returned and restocked.

Now....I do not have an issue with this ...if it were done properly and was purchased by an HONEST PERSON.



Whomever had previously bought this kit and returned it....had PILFERED THE KIT...for the special double lipped outer piston seal...and put one of their old, used single lip seals back in the box.

They had also taken the new brass flap valves and put back their old ones. They took the boot and put nothing back in. They took the new spring mounting screw and put nothing back in.

If I ever hear about anyone admitting that they have done this anywhere on these forums...I will make a note...and if I ever meet you in person I will do my best to kick your ass!

Of course RockAuto will refund my money. It was only $8. I dont care about that.

BUT...I have done a lot of brakes. I...easily noticed the most important and critical parts of the kit were gone or used and worn out. Many people would not.

A LOT of inexperienced and newby people frequent RockAuto for parts. Many of them would not recognize the issues I listed.
Installing these parts is a master cylinder could EASILY get someone killed because the brakes WILL be substandard.

If you are going to "mine" odd part # kits for parts...be honest about it, pay for the parts and throw away what you do not need.

OK..back to business:

For type 4...you can have either FAG/Schafer or ATE cylinders. Both were OEM and both are equal.

HOWEVER....you CANNOT swap internal parts between FAG and ATE cylinders. They DO NOT match!


I will say that the design of the pistons and the smoothness of the casting of FAG cylinders is a little more elegant than the ATE products...but in quality, fit and finish and performance they are 100% equal.

This is my small collection of FAG pistons. The springs and other parts are in the box.

This is my small collection of ATE pistons sets. The sharp eyed among you will notice....that something is wrong here in this picture. You can see it with the left most piston.

And here it is. The piston on the left is NOT a type 4 piston and will cause major grief as the piston head is in the wrong place for the replenishment port.

Here is the wrong piston from the left...and it has a different part #

Here is the normal ATE type 4 piston from one of the sets on the right. Correct part #.


Also....very important!!!!!!

BUT...and I am measuring to be sure.....that shorter piston shown above...may actually be an ATE built rebuild kit piston for an FAG master cylinder....yes...that level of insanity existed. Many years ago I could buy Schafer branded and ATE branded rebuild kits for both FAG and ATE specific master cylinders....and God help you if you mixed them up....see below for the difference in ATE and FAG.

The FAG primary piston is slightly shorter in piston head length than the ATE...which means that the fluid port cast into the cylinder is in a very slightly different spot. You "may" get away with it.....but you are risking your life.

Next up....type 4 clutch master cylinder differences:

I have never seen an ATE brand clutch master cylinder for type 4. This does not mean they may not exist.

As I warned...never mix pistons from one "type" of cylinder to another because fluid port dimensions/locations in the casting must match the piston head locations.....and this is especially true....in dual circuit brake master cylinders.

However there is an exception to every rule. In the case of single circuit master cylinders like the clutch...as long as the piston length, piston stop length, diameter and fluid volume and spring type and length are the same....you can get away with it.
There is usually no chance that the fluid inlet ports of the cylinder casting will be anywhere near the two piston heads to be blocked.

Case in point:

On the left is the FAG piston from the 411/412 clutch master cylinder. On the right...is the FAG piston from a Vanagon clutch master cylinder. These will Install with no issues.
Even though there are visible differences....thicker outer seal etc....I have bought rebuild kits and slapped them in numerous times with no issues.

With these you will not be able to steal just the outer seal. It is a different thickness.

However you can take a seal and flap valve from an FAG or ATE brake master cylinder and use it to rebuild your FAG clutch master cylinder piston.

More to come. Ray

[Chris Walden]

If I recall correctly, (it was a long time ago, after all) my local Beck Arnley, BAP/GEON stores didn't even list a clutch master cylinder rebuild kit. It was me that discovered that half a brake kit worked. On the other hand, I'm also remembering how many left foot shoes were ruined and possibly it wasn't a particularly effective fix.

Chris

[raygreenwood]

[raygreenwood]

This is an excerpt from the type 4 master cylinder in trunk modification thread. Since is delved into exactly what I was going to start talkng about here...I am moving the quotes over.

Ray Greenwood said:

[raygreenwood]

Update for 4-1-2017:

So over the next week or so...some of these projects will pick up a bit.

First a couple of important items of information:

1. Using alternate parts kits:

There are risks with this practice...aside from the fact that you cannot use the actual pistons from these kits if they are not for your exact master cylinder BRAND AND CASTING

As I noted, I have been buying cheap 19mm MC rebuild kits off of RockAuto whenever they are dirt cheap...to be able to get new piston seals, flap valves and boots.

I recently bought kits for a VW Thing and an early 70's beetle for about $4 each.

If any have ever rebuilt a master cylinder and have had to install new seals on the pistons...you know its very tough to do without the factory tapered install mandrels. I have been trying a wide range of tapered hubs over the years and its very tough to do. Have not found a replacement yet...but have learned some tricks I will relate as we move along.

The issue...and I have been warning about this for years with regard to NOS brake parts....is that the two kits that came in last week or so....have two issues that can kill you:

One of the boxes. As noted...these are EIS products. They are/were...a major manufacturer of aftermarket brake repair parts. A very good one.

They were acquired in the early 1990's by Standard Motor Products (SMP). Shortly after that..even though I believe their factories are still in production....EIS ceased to be a brand in itself you would see unless it was OLD STOCK.

So with no UPC or bar codes that places these EIS brand parts at late 80's to early 90's....and that is important.

These are really good quality parts in that they use piston castings that are straight from the original manufacturer. These pistons have FAG/Shaffer cast into them. The machine work is excellent. Too bad I cannot use the pistons.

Risk/issue #1: As I noted...one kit was "pilfered" long ago by someone who bought the kit and returned it. The primary outer piston seal was missing, the seal cups not in bags and the original buyer replaced the new flap valves with his own and returned the kit. Watch for these issues when buying an NOS repair kit

It looked like this coming out of the box. The seals not in the bag, one seal missing and the pistons no longer wrapped in anti-corrosion paper or bagged...and the outer boot is missing.

Here is what the other kit looked like..and was proper. Pistons wrapped, seals in bag everything there.

Risk/issue #2: I have gotten pretty good at installing new seals on pistons over the years. Its still hard. The primary piston seal on the outer piston...is not that hard. Of course the seals that go under the spring support cups are easy...just slip them on.

But...the 2nd seal on the inner piston...can absolutely kick your ass trying to get on.

Typically the factory tapered seal installation mandrels cover the upper seal slot. Some of them actually do not cover the upper/outer seal slot...and require you to install the upper/outer seal first and then once you get the inner seal slipped over...you have to fight the inner seal over the other seal into its groove without damaging either of them.

The problem I found ...and have been warning about...is that ALL OF THESE SEALS in these NOS kits...are old enough that have hardened up.

I fought for two hours to slip one of these seals over a piston head. I could not get it done without ripping a seal.

So....I pulled out my Rex model 1500 durometer gauge (I just got it recently)

Let me tell you the difference in the seals that are NOS late 80's/early 90's...and the seals from old used pistons that were known to be manufactured in the late 90's to maybe 2001.

Both are still old....but the NOS seals are a decade older.

Late 90's used seals durometer: 42-45D shore A

NOS late 80's seals durometer: 58 to 64D Shore A

...yes...they harden up that much.

The NOS seals will still work in an MC....because they have not been contained by the bore of the MC while sitting on the shelf hardening up......IF..and its a big if...if you can install them.

They will however have issues with lifespan if your MC has to be honed or is at the upper end of the factory tolerance limit.

Risk/issue #3:

As I have noted...there are slight differences between manufacturers. The FAG and ATE cylinder castings....at least for type 4..are very slightly different as are the piston head spacing on the primary.

To add to this.....the FAG/Shaffer inner piston, top seals...have a slightly different cuff length that cause extra movement on the seals cups if you try to install them on an ATR piston....that can cause your brakes to fail...if they initially bleed at all.

I will post pictures tomorrow.

Ray

[raygreenwood]

Update: Basic master cylinder Rebuild:

So a short update and a start. So this thread is about brake hydraulic cylinder
"RESTORATION"...but there are numerous levels to that.
One mans full factory restoration is another mans waste of money...if all you are trying to do is get the car off the side of the road.

So as originally noted there are different useful levels of brake cylinder reconditioning. Let me list them:

1. The basic low miles master cylinder refurbishment:

This is when you bought a NEW (not remanufactured or rebuilt) master cylinder say 5-6 years ago, have religiously kept your brake fluid flushed every two years and the seals are starting to bypass from many miles and age....or the fluid is starting to look dark.

When disassembled the master cylinder bore is flawless...no rust or scoring, the pistons are clean...no corrosion or "white rust" and the brass flap valves are clean and flat with no corrosion.

This is simply be either a new piston and seal kit, new outer boot and new copper stop bolt washer and reassemble.

2. Basic rebuild for a master cylinder rusted slightly inside and/or outer seal leaking:
This is the type of rebuild I will be doing first...the harder way

This is a complete rebuild...but not a restoration. Meaning there is corrosion on the brass flap valves and on the piston heads under them, the seals and boot are shot and there is light to moderate rust in the bore. This may even be a master cylinder core you pulled off of a wreck or off your years old shelf of used parts.

The goal is just getting it back to correct function and NOT a full RESTORATION or preservation job. You just need to get the car driving again.

You will either be doing it the simple way IF you can find a kit for your MC with new pistons and seals.....

Or you will be doing it the hard(er) way....which is acquiring seals, flap valves and boot from a repair kit from a different model car (again discarding the pistons from the repair kit).....and....cleaning up the corrosion on the flap valve sealing faces on your old pistons that you must reuse.

Either way....this type of rebuild is nothing special. No special coatings, plating or painting. Just clean it, reseal it...and get it back in the car in functional condition.

This level of rebuild...for a cylinder .with some rust and corrosion damage... can be done only IF the master cylinder bore diameter versus the piston diameter of the pistons you are going to use...have enough tolerance left for a very LIGHT hone.

Common example:

Piston head diameters: 0.7485"
Bore diameter (before cleaning and honing): 0.751"

Measured P to B tolerance/gap: .0025"
Allowable P to B tolerance: .004" (a max of .0045 to .0075" can be used but life may be shorter)

So you can afford to hone the cylinder only .0015" to .0017".

You have small rust pits that are estimated to be about .003" deep near the outer seal and a ring shaped rust pit where the inner piston seal rests that is about the same. You can get away with rust pits of about .0015" to .00175" deep....and seal with few issues.

This means that you will have to hone the bore to its maximum of .004".

Some piston heads can vary by as much as .0005" to .00075" within a set so if you have several sets of old pistons to play with.....measure them with a micrometer...not a caliper....and use the larger ones.

Some bores are at the extreme of tolerance already from the factory and usually matched to slightly larger pistons. Its not uncommon...especially moving into the 1990's and 2000's to find a factory MC bore as large as 0.752" to 0.753" with pistons that are right at 0.749" to 0.750" that still keep the cylinder fit right in the factory tolerance.

When cylinders come from the factory at this tolerance level.....they are really hard to rebuild properly except when they are a basic "clean" rebuild.
If they have to be honed to remove pits....they are only candidates for a complete restoration.



3. Complete cylinder restoration:

This is for when you either have to have something that "looks" like factory...as well as functions like new. Or....when you cannot get new master cylinders and must re-use a very rough core master cylinder.......and/or....if because your master cylinder or brake cylinder IS rare and you want to restore it AND extend its life so it will likely never wear out in your lifetime.

In this type of rebuild which we will be doing in a couple of months...it entails either replating the bore and/or pistons to bring them back into tolerance...and make them more rust proof than they ever were from the factory....and/or boring and sleeving with brass or stainless (I will try to do one like that as well).......and stripping chemically to remove and neutralize corrosion and both plating the cylinder externally and painting or coating.

As I noted....I will be doing the #2 method to start with and in the process demonstrating the simple clean rebuild of #1.

I will be using 20 year old cylinder and piston cores that have been in a bucket. Ray

[scott3t]

Ok Wow! So much good information. I'm about to start what may never end I fear. But I could never attempt this without all the great information in these posts. I am about to start the restoration of my '74 412 two door manual that I've had since '76 (in the family - acquired from Mom in '87). Basically in storage not running since 2001.

I'll start a new post for the restoration, but like Ray mentioned in some post I remember reading, brakes can prevent the vehicle from ever moving (I'm paraphrasing) so I think I'm starting there. If I know it will stop, I can move to getting a body and engine that will work. So I'm looking at this post and the caliper rebuild part 1 and 2 post and hope to start soon.

This is a bit intimidating to ensure I get the right tools, parts, oils, acids, pastes, lapping, plating, and honing but I appreciate all the great detail. With help from the forum, I hope to get there.
-Scott