The RISK of NOS brake cylinders/titan3c’s master cylinder refurb

[raygreenwood]

For years I have been warning of the risks of buying NOS brake master cylinders. Simply put…if they are old enough to be called NOS (meaning old and out of production)…and production didn’t just end 2-3 years ago…..they can have problems. Really the problems start to rear their head when they get over about 5 years old on the shelf.

The rubber in master cylinder rebuild kits starts to get stiff enough to be a problem installing when it gets over about 10-15 years old. If the kit has new pistons you may be fine for installing them but they will still have a shorter life.

So the moral of the story is….unless you get a REALLY good deal on an NOS brake master cylinder…and you really need it for the hard parts and plan to install new seals scavenged from another kit (meaning you just need a good core)…..don’t pay the usually exorbitant price of NOS if you have any other option.

This thread is “somewhat” of a how to….but is mainly an illustration of the issues with NOS cylinders.

So titan3c (Bob) found what I consider a very good deal on NOS type 4 master cylinders. It was worth the risk because:

A. The price was not bad for taking the risk

B. The seller had numerous in the box and had a warranty. If it does not work…return it for replacement.

So I was in agreement when titan3c noted he rolled the dice on buying one. When it failed to bleed properly for him no matter what he did….I offered to put new seals in it for him. I did this for several reasons:

1. Bobs a nice guy…..and I don’t know if he has any gallery pictures up but his 1971 VW 411 4 door Complete with vanity plates)…..looks superb and is in REALLY great shape….and its too easy to help on something as simple as this.

2. I have boxes of seal kits around I acquired cheap for ATE and FAG cylinders…mostly type 3…that I can scavenge for seals.

3. These cylinders have not been manufactured except for factory rebuilds through people like A=1 Cardone and Beck Arnley…since about the mid 1980’s.

I wanted to get a look at an NOS 411/412 cylinder because I have not had one in my hands for years. I have better tools now including better bore measuring tools and a durometer tester to get a handle on how much the seal harden up over time.

Lets get on with the show:

Warning:
Even though you see me using FAG and ATE pistons in these photos….they are NOT interchangeable. ATE pistons fit only ATE cylinders and FAG cylinders fit only FAG cylinders. Some seals and parts can be interchanged….but NOT the pistons themselves.

A lot of the really deep details about techniques for changing the piston seals will be in the brake hydraulic restoration thread.

So this showed up in the mail. Externally..…a pristine ATE MC.

First order of business is to clamp it in a vise between two blocks of wood. No teeth marks from me!

Off with the boot. The little crusty bits in the picture are dried up assembly lube.

I use a blunt screwdriver with a polished end (broken off…then polished…you know how it goes) so I do not scratch the zinc chromate on the washer underneath. Scratches rust faster. Pry the long leg of the spring clip away from the groove.

Lift it up enough that you can get a grip on it

And grab it with needle nose pliers and pop it out.

I pick up the washer with a magnet or you can just tip the cylinder over and it falls out.

I use a fat, blunt Philips screwdriver as a “pusher” to not scar the piston. Just push it in as far as you can and release it quick.

It will spring up about this far so you can get it out.

I use plastic stereo fascia removal tools (Harbor Freight…$5) for prying delicate parts like this.

What I found….this is the PRIMARY problem with NOS brake master cylinders:

The piston on the left is the piston from Bob’s cylinder. The one on the right is a brand new FAG piston ….but the differences you see in the seals is the same for either make.

Notice the “square” side profile of the ATE piston on the left compared to the flared shape on the piston on the right. The ATE piston has been constrained for decades by the cylinder while the EPDM rubber hardened up. It takes on the shape of the cylinder and cannot flare out and seal properly under pressure.

Moving on to the inner piston set…..

First…just crack the 6mm lock screw loose. Do not remove I t yet……

….until you have a pusher rod to push the inner piston down below the bolt just a little bit. This is a plastic rod so it will not scratch and will not leave debris. You can use a wood dowel or a socket and socket extension but I recommend wrapping both of those in tape so you do not scratch anything or leave wood chips in the bore.

Rap the cylinder on a block of wood or plastic to start the inner piston out of the bore…and then use the same technique as you used to remove the outer piston.

AND….the main defect rears its head……!

Notice that the spring, spring seat cup and inner seal did not come out with the piston? Not unheard of…..but the seal did not come out with the piston either….NOT common!

I fished the seal out of the bore….and it came out in two pieces! Split…because it’s hard as a rock.

The brass flap valves were caught just in time. These are tarnish/oxidization spots from the compensation ports. They can be reused. I will lap them lightly to remove the tarnish. Another few years and they would have been beyond use.

When you find these with green corrosion on them they are usually too far gone to lap smooth because the green corrosion is displaced metal and it leaves surface pitting. Sometimes you can flip them over if the side against the seal is not corroded green.

I have new ones in the kit but we will get to that in a minute.

So…..removing the old seals from the inner piston. I will get into techniques and tools for seal removal in the other brake thread…but the top one came off ok. Only moderately stiff…….

The next seal down is a little harder. It has to first be moved into the seal groove above it and then over the next piston head as well. Double the work.

And…it snapped getting out of its own groove. Its significantly harder rubber than the seal I just took off right above it.
And remember….that the seal 1.5” away on the bottom of the piston next to the spring literally shattered. We will get back to this in a moment.

This is the primary/outer piston. Make sure you clamp the piston securely. Use a quality screwdriver with a blade that fits the screw perfectly. These screws do not grow on trees.

Once the screw is out the spring pops right off its spring seat.

Seal pulls off and the brass flap valve comes out. Same condition as the inner one. Caught it just in time.

Removing the double lipped outer seal was very easy. It is still quite soft even though its lips are now misshapen from being in the bore so long.

OK…..now that it’s completely apart…back to the variable seal hardness issue. Both of the seals on the outer piston while shaped poorly and harder than new ones….were soft enough to come out easily….while the very inner two seals on the inner piston either completely shatter or snapped easily.

So why that much difference in one seal set? Well….the hardening effect you see on the inner two seals is what you expect to see with EPDM….when it is exposed to petroleum distillates or petroleum based oils or greases.
So do I suspect that the wrong lubricant was used?....no. If that were the case the outer two seals would be rock hard as well.

What I suspect is that the cylinder was not rinsed well enough after the original machining and still had cutting oil or anti-rust lubricant in it on the inner area of the bore only.

One would ask…..do you really think that ATE or any German manufacturer might be that sloppy?.....YES!

I have been telling people for years that these cylinders are not made in a “clean room”. No manufacturer’s cylinders are. I disassemble every NEW master cylinder I buy and clean it out. You would be STUNNED at the crap that comes out. Cylinders from Brazil and Mexico are the worst. Even worse than I have yet to find in Chinese cylinders so far.

This is the crap that came out of Bob’s NOS cylinder. That is denatured alcohol. I was careful to ONLY rinse the inside so I could show you this. This is about average. The Brazilian and Mexican cylinders have much more crud in them.

I am not worried about this debris scoring the cylinder walls. I am worried about it propping open a flap valve and have had it happen on several occasions.

An important word on cleaning products:

Use denatured alcohol ONLY. Surprisingly…EDPM rubber is ok to use MEK on…..but I would not because in the long run it can start to dry it out.
DO NOT use Isopropyl alcohol. DO NOT use brake cleaner. Use dish soap and water if you have nothing else.
Methanol and ethanol are safe to use with EDPM…and are the main ingredients in denatured alcohol.

Locally I found these two. Do NOT use the “green” product on the left. For some reason it contains ethyl acetate along with ethanol and methanol. While ethyl acetate can be used for a limited amount of time on EPDM….why take the chance? Whatever denatured alcohol you buy…pull up the MSDS/SDS sheets on line. Make sure it only has ethanol and methanol in it (along with the denaturing ingredient)

Back to the seal rubber……

I simply pressed on the inner seal with my fingers….and it literally shattered. So…..

.…I put one of those little chunks on my granite plate and applied my trusty durometer tester (Rex model 1500 shore A)….and….

…it reads 85 durometer. For comparison your tires are about 50-55 durometer. Brand new EPDM windshield seals are about 45-55 durometer. Brand new master cylinder seals are usually about 50 durometer at the softest and 60 durometer at the hardest.

The outer piston seals were actually not bad as far as hardness goes and even with the flattening of the cup lips, I think Bob noted that he only had REAL issues with the inner circuit.

The new seals in the kit are just a bit under 60 durometer. The instruction on this tool note that if it’s equally above one number and below another like in the picture its exactly halfway in between so this is right at 57.5 durometer.

Ok…so earlier I mentioned that I am reusing the brass flap valves instead of using the new ones from my kit. Here is why.
Take a look at the new flap valve from the FAG kit on the right. Notice that it has a very slightly larger ID? The ID of the boss on the outer piston of the FAG kit is .439” and the boss on the outer piston of the ATE piston is .414”. That’s a respectable .025” difference.

In the past in a pinch I have used them. While they shift can shift around .025”…they do not uncover the compensation ports. But since his original flap valves were in such good shape I did not want to risk any oddities.
The seals themselves fit fine and I only find this on the outer piston of “some” FAG kits.

So I have a little tool I made for lapping the brass flap valves. It’s a piece of soft silicone rubber attached to block of hardwood with tape. I lap the flap valve on a very fine oil stone in a circular motion. You can also use 1500 to 2000 grit wet/dry on glass. It takes about 30 seconds of work. Then wash it in denatured alcohol.

VERY IMPORTANT:

About the seals themselves and the differences between them:

And for the record….the inner piston is the “primary” piston and the outer one is the “secondary” piston.

There is some confusion and “near” errors and issues in some of the books out there. In the Haynes manual for VW 411/412 (Green manual #091)…..it is stated that (no matter which brand the master cylinder is….ATE or FAG) the primary piston (the inner one) has three seals that are all the same shape and size.

This is incorrect. It does have three seals. The two close together ones are of one design…with a slightly longer inner sleeve and angle.

Haynes states that the two seals …one on each piston….that are next to the spring for each piston are the same. This is correct but they have a slightly different profile than the other two on the primary piston. Because they have an inner steel support cup for the spring they do not require the longer inner sleeve.

Haynes correctly lists that the outer secondary piston seal is unique. It has a double inner lip to seal the piston against leakage to the outside.
In the very beginning….ATE had a diagram in many of the shop manuals that showed that the two close together seals on the inner primary piston had “ribs” to identify these seals. In the old days…that was true.

After a while so many people were making these seals that I found some ATE sets with no ribs…..and some FAG sets like this one I am suing…where they are ALL ribbed.

Also for the record:

ATE is ATE
Schafer is FAG. And…..
Schafer also made rebuild kits for ATE and Girling and others that are sold under just the Schafer name. And many new rebuild kits are branded Schafer-FAG.

So….the moral is look at the seal shapes and sizes you take off your pistons and match them to what fit correctly.

For the record….long in the past before I knew there were subtle differences in seals…I have mixed them (think high school). I never had any “REAL” problems but there were issues now and again with bleeding.

So here is the new seal set. The one on the far right is the double lipped outer piston seal.

You can see the differences. This is where they fit. Don’t mind the crusty FAG piston for reference.

A little closer view. Notice the flat floor on the seal on the right. These go under the springs on both pistons. It needs the extra room to accommodate the steel cup that holds the spring.

Here is the side profile to match that last picture and the difference is also evident. Also notice that ALL of these cups have “ribs”…go figure!
Reassembly…..

Secondary/outer piston…..flap valve on first.

Then the seal cup. Notice the flat floor in the valley of the cup……

….to make room for the steel spring mounting cup. Then install the spring and spacer

Then install the locking screw. I have no torque value for this but just make it tight and realize the pistons are magnesium so do not get crazy. It’s a 3mm screw with fairly high grade steel. Its estimated ft. lbs torque is somewhere around .80 to 1.1.

I flip the piston over and I lubricate the groove with pure silicone oil….because I have some. Otherwise use brake fluid. Brake assembly lube is excellent but almost not slick enough for putting on seals. The silicone really helps….but if you buy some…read the MSDS sheets and make sure its PURE silicone oil with no petroleum distillates in it.

And install the seal.

NOTE: As I noted I will get into seal install details in the brake hydraulic restoration thread. This thread is mainly about the issues of NOS cylinders and getting Bob’s cylinder back together.

Notice how well the seal lips flare out compared to the NOS cups.

Now the inner piston. This one is a pain as the inner seal must first pop into the outer groove…and then you have to work it over the thicker piston head and into the lower groove. The lower cup faces downward/inward and the upper cup faces upward/outward.

Same process as the other piston….lube with silicone oil and install cups.

Piston flipped over to add the flap valve cup and spring

The flap valve installed

The seal cup. Again…note the wide valley floor on the cup.

The steel spring cup and spring.

Both pistons are done.

IMPORTANT NOTE: after using silicone oil for assembly lube you MUST re-wash the pistons and seals in denatured alcohol to remove the silicone oil.

I have some factory Porsche brake cylinder assembly lube. Smells like fish oil!

Install the 6mm set screw…..but with ONLY 1-2 threads engaged.
CAUTION: You need to put this screw in place now because you will need three hands in a moment.

BUT…..only engage the first thread. Look into the bore with a flashlight to make sure the tip is not protruding into the bore. If it is you will damage the piston.

Lube the piston seals and piston heads and swab the bore as far inside as you can reach.

I push gently and use a plastic pick to tuck in the cup seals. Then use your plastic rod or padded bar to push the piston to the bottom of the bore.

Screw the 6mm stop screw all the way in and make sure it has the copper washer seal. Torque this screw to 3.6 to 7.0 foot pounds. You can now release your pusher rod and the piston stays in.

Lube and install the outer/secondary piston using the plastic pick to help the cups in.

Ready for the washer and spring clip

Washer is in

Push the piston down with the blunt Philips screwdriver and feed in the clip with the small leg on it first

The clip drops right in with some pressure. Tap it to make sure it is seated.

And…back where we started…but better. Now to replace the boot…..and done…almost….

NOTE: the bronze colored coating you see on these and many other “magnesium” pistons is a special chromate coating called “Alodine” made to protect magnesium.

Magnesium is designed to corrode or create “white rust” when exposed to air and moisture to form a sacrificial coating on itself to prevent heavy corrosion….but it does keep oxidizing over the eons and the white corrosion is enough of a contaminant and it makes a less precise surface.

So large expanses of non-machined areas that do not generally get encapsulated by assembly lubricant until the brake fluid gets filled….are Alodine coated.

This does not prevent corrosion of magnesium….but it GREATLY slows it down….by about a decade…by preventing oxygen from reaching the surface.
You can find VERY old NOS magnesium parts that come out of boxes that appear to have a paper thin shell or skin that sloughs off….that many people mistake for “Cosmoline”. It is actually Alodine coating.
When it gets old enough, moisture and oxygen permeate to the magnesium and the magnesium forms a complete film of white rust that separates the Alodine coating from the surface.

Other important notes before we finish:

Partly just for reference….there are some slight differences between the FAG and ATE rubber bungs for the filler pipes. Generally they are interchangeable but in some rare cases the quality of the casting can make fit of the wrong brand in the wrong cylinder difficult.

The ATE grommet

The FAG grommet

The two next to each other. Subtle differences.

The very important point to all of this grommet stuff:

Notice the recessed ring on the inside. This is NOT enough in all cases to allow the inner lip of the plastic supply elbow to be fully recessed enough….to prevent the elbow from sitting flush on the cast iron floor inside the grommet hole. This seals the end of the pipe and prevents flow of fluid in or out.

In many cases…..this can prevent bleeding enough that the cylinder is thought to be defective.

This illustrates the issue.

To prevent this and easy fix is to notch the opening on the inside with either a Dremel tool or a triangular file. Use a razor blade to carefully deburr this when you are done.

Some final Notes on titan3c’s master cylinder:

1. The seals were classic very old NOS….some hard as a rock….all misshapen with age and constriction.

2. But…the bore, casting and pistons were pristine. Worth what he paid for it just for the core.

3. The bore measurement was 19.08mm/0.7515”. The advertised spec for master cylinder bores is 19.05mm or exactly 0.75”. These are allowed a maximum oversize of .004” or .1016mm.

It is common for factory new cylinders to be somewhere in the middle of that allowable .004” specification. So…having it .0015” larger than 0.75” is normal and quite good.

If one is careful to not let it rust before it is rebuilt again…and only a light honing using a 600 grit or better hone is used…..it can probably be rebuilt at least twice more before it is oversized.

Ray

[titan3c]

Ray, this is a great presentation. I have learned a lot from it, and looking forward to installing the mc. Thought it may be interesting to everyone that the original brake line installation on my car(from the factory), was on the bottom connection of the mc, but should have been on the top connection. The reasons were discussed in another thread. So I'm changing to the top connection where they are suppose to be. Well small problem---the line nearest the push rod end of the mc is just too short to make connection to the top. The best solution I see is to cut the line(which I hate to do), about three or four inches down, and fabricate a connecting line that will reach.

[raygreenwood]

[HenrikL]

Wow, very nice and informative thread.

[titan3c]

I have worked the line to be as straight as an arrow, but the bubble flare will just barely reach the mc opening on an angle, and I'm afraid if bending it anymore will kink it. I'll give it some more effort, but I have doubts that the line will reach it. The only other thought I have is going under the floor board, and see if there is any possibility of getting some more length between there and the wheel connections. Bob

[raygreenwood]

[AhnwS71]

"Lube the piston seals and piston heads and swab the bore as far inside as you can reach. "

What type off lube should be used here?
_________________
'71 Westy

Sometimes you eat the bar, and sometimes the bar eats you. the Stranger

[raygreenwood]

[heimlich]

This is a great writeup. It should definitely be a sticky somewhere but I a bit biased since I have so many NOS master cylinders.

Ray is absolutely correct. Do not take a NOS master cylinder and throw it in the car. There is at least a 10% chance it will fail. It will most likely fail within a few years otherwise. The big thing is if both cylinders fail at once you won't be stopping.

I do sell these master cylinders and (for now) I provide a 311 kit with new seals in them. The 411 kits are not available and when they are they get very pricey.

Are you able to find brass ring/washer replacements?
_________________
www.vwnos.com [email protected]
Classic Brands. Classic Quality.
Not all parts are made the same. NOS OE/OEM parts made mainly in West Germany, Early Germany, and Early Brazil are where VW produced the best quality parts and best fitting products.
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[raygreenwood]

[heimlich]

Just pull some seals from a NOS master cylinder. If you want original quality just copy theirs.

Ray can you rebuild a master cylinder in under an hour? How much would you charge for something like that to put new seals in?
_________________
www.vwnos.com [email protected]
Classic Brands. Classic Quality.
Not all parts are made the same. NOS OE/OEM parts made mainly in West Germany, Early Germany, and Early Brazil are where VW produced the best quality parts and best fitting products.
5% Off your order with coupon code: 5%OFF
Restored Distributors Available (<--Click here)

[raygreenwood]

[mattlockwood]

[raygreenwood]

[mattlockwood]

Thanks Ray- you are very knowledgeable on this topic for sure.

Last question- how do you coax the rear piston out of the bore if there is no screw holding it in? Tap the MC with a block of wood or the like?
_________________
1970 Bay Window Bus.
110 hp 6 cyl Aircooled automatic

[mattlockwood]

Answered my own question- you can tap it out gently.

Thanks for this writeup, used it to clean my MC. Look at the dirt and debris in the denatured alcohol bucket....

_________________
1970 Bay Window Bus.
110 hp 6 cyl Aircooled automatic

[raygreenwood]

[mattlockwood]

It’s an aftermarket German made, but with only a few miles on it when removed.
_________________
1970 Bay Window Bus.
110 hp 6 cyl Aircooled automatic