Clutch Master Cylinder / Clutch Pedal Rebuild

[Bill K.]

I'm rebuilding spare clutch master cylinders as my daily driver has begun to leak.

Cylinder Honing Max Diameter?
One spare cylinder honed up nice, the other has some pitting along the lower quadrant of the secondary seal. Both cylinders are FAG. I'm using a Type 3 ATE kit which has a Table of Tolerances indicating that a nominal 19.05 mm cylinder bore cannot exceed 19.16 mm (.754 inch). I've worked it for several minutes using a 19mm flex-hone and brake fluid for lubricant, but the pitting is still present with the bore opened up to .752 using calipers (so actual diameter is larger). I'm looking for advice on proceeding with further honing or relinquishing to the scrap pile.

Primary Seal and Backing Washer?
The Type 3 ATE kit (311698181C) has identical secondary seal as the 412 FAG clutch master cylinder. However, the T3 primary seal and backing washer has smaller inner diameter (.030) than the T4 units so they don't fit the piston. The T3 seal can be forced on to the T4 piston, but the backing washer is brass so it won't fit. I've turned down the T4 piston to the same size as T3 piston to fit the T3 primary seal and backing washer. The idea is to restore the T3 seal fit to the T4 piston and be able to replace the NLA T4 backing washer with new T3 parts. Bad idea?

Pedal Slop?
My clutch pedal and push rod clevis has side-to-side slop. Before the leak started, the pedal squeaked... A spare pedal cluster has the same problem. The slop looks to contribute to the seal failure as the piston gets biased in the bore by the rod/clevis slop. Is it wise to replace the pedal bushing and fix the clevis slop so the piston doesn't get side-loaded and prematurely wear one side of the secondary seal?

Thank you,
Bill

[Bill K.]

Pictures of above.


Pitted clutch master cylinder (at 2-3 o'clock position) after honing to .752+ inch


Top, left piston - stock 412 clutch master piston
Top, right piston - modified 412 clutch master piston for T3 brake m/c primary seal/washer
Top, left seal - 412 clutch master secondary seal
Top, right seal - 412 clutch primary seal (note larger ID vs. T3)
Bottom, left seal - T3 brake secondary seal
Bottom, right seal - T3 brake primary seal
Bottom piston - T3 brake secondary piston


Clutch pedal clevis slop


Clutch pedal rod pivot wear (note elongated hole in clevis and pedal left/right; combined with pedal pivot slop, results in left/right slop to bias piston in cylinder and wear secondary seal?)

[raygreenwood]

Bill, In general....the rebuild parts will not swap from ATE to FAG and vica-versa...for the reasons you have found. If you can turn down tehFAG piston...you can use the inner cup seal and brass flap valve from the ATE. That inner cup set by the spring by the way...is the primary. The outer seal is basically a shaft seal. Still critical...but the inner seal makes the pressure.

Unless the pistons are 100% identical in every length and dimension it is not wise to use the actual pistons from one make to another...because if the piston flange location is off by a fraction...many times the piston face will block compensation ports starving the cylinder. You are wise to try and rebuild the FAG piston for use in an FAG cylinder.

That being said...be careful with the outer seal as well. There were a few subtle differences on some makes.
In general I have found that seals from ATE type 3 brake masters will fit both ATE type 4 clutch and brake cylinders. FAG type 3 seals will also fit FAG type 4 cylinders. In general type 3 pistons from brake masters cannot be used in type 4 cylinders. Just the seals. Too many different compensation port locations in the castings over the years to make it worth the risk.

The maximum cylinder diameter listed...is correct. When you hit .754"....it will be hard to keep the outer piston seal sealing properly.

The problem with these clutch slaves and even the type 4 brake masters is that they are inside of the vehicle. There is too much trapped moisture in the air. In condenses onto the outer cylinder area making a rust ridge in short order that destroys the sealing area...and creates the pits you are fighting. The only way I have found to fight this....is to for sure fix leaks in teh car that keep excessive moisture in the vehicle...and spot glue a small calcium dessicant bag inside of the boot near the end so it does not get caught in the piston....and for sure every other year...simply remove the cylinder (I know..ugly two hour job)..and clean everything.

One other really good option is this: http://www.google.com/imgres?imgurl=htt ... s%3Disch:1

The vanagon clutch master cylinder is the same diameter, bore and stroke and except for small issues on the inner end....the same volume and piston pattern as the type 4.
If you look closely...you will see that if you added a simple angle iron plate to the bottom of the vanagon master cylinder...it will bolt right up to the type 4 pedal cluster. You will have to make a hose stub or angle adapator to connect up to the fluid outlet....but it whouls work well. I cannot remember if the residual pressure valve has the same thread or not. I can check tonight. I have a couple of vanagon MC castings.
The seals work perfectly though.

The worn clevis hole is a PITA. At one point I madea new one out of a piece os teel rod and reamed teh hole round by about .010" Ray

[Bill K.]

Thanks again for the info Ray.

Are there different sytles of T4 ATE clutch master cylinders? I have a RHD ATE clutch master cylinder that uses a different inner (primary) seal (I mistakenly switched terms primary and secondary above and have now fixed). This style of of inner seal obviously isn't compatible with the FAG cylinder, so there must be a later T4 ATE design that works with the later T3 brake seals. If you have one handy, please measure the T4 ATE piston OD's for both seals.



For the vanagon cylinder, please elaborate on the issue:

...except for small issues on the inner end....

That looks like a good alternative.

Bill

[bradey bunch]

I replaced my clutch master with a 1980 vanagon one and it works great... and its BRAND NEW. no reused stuff here. just a piece of angle iron with holes drilled for the bracket.
I like the idea of taking out the slop though, my pedal squeaks... ill have to look into that.

Nice work as usual Bill.

Braden

[Bill K.]

Thanks Braden. Does the vanagon cylinder line-up on-center left/right with the pedal push rod when the bracket is designed properly? It seems like a 1/8" thick angle bracket would work. Did the T4 residual valve thread fit the vanagon cylinder? Got a picture?

[hoodsy]

aww that's a bummer Bill, I had or have the fag clutch master cylinder rebuild kit. i tried to fix my master cylinder with it but Mine is ATE, and well of course it didn't fit. too bad we couldn't have swapped kits. I needed the one you have, and sounds like you needed the one I have. I will check and see if I see have it around, if I do you are welcome to it, but I am not sure if it is around or what condition the parts are in, but i will check. Incidentaly I was able to just soften up my original seals a bit with a light oil soak and they haven't leaked since, that was a couple of years ago. anyway i will check my spares and see if the fag kit is still around, like i said you would be welcome to it, as i doubt i will ever have any use for it.also if you have a good measurement of the seals, there is a seal maker/supplier here in Vancouver B.C., that has always been able to supply me with just about any seal i am looking for or at least a decent usable substitue provided they have a sample. They are called Ryson seal, I will see if they have a website or get an address if you like.

[bradey bunch]

I didnt think this pic turned out, but upon review it looks like it may help.

I used washers to space it up so the rod would align with the cylinder. The bolts on the master go in from the bottom. No residual pressure valve was used. A new hose for the attachment to the resivoir is highly reccomended.
Let me know if any of it needs more clarification.

[raygreenwood]

aww that's a bummer Bill, I had or have the fag clutch master cylinder rebuild kit. i tried to fix my master cylinder with it but Mine is ATE, and well of course it didn't fit. too bad we couldn't have swapped kits. I needed the one you have, and sounds like you needed the one I have. I will check and see if I see have it around, if I do you are welcome to it, but I am not sure if it is around or what condition the parts are in, but i will check. Incidentaly I was able to just soften up my original seals a bit with a light oil soak and they haven't leaked since, that was a couple of years ago. anyway i will check my spares and see if the fag kit is still around, like i said you would be welcome to it, as i doubt i will ever have any use for it.also if you have a good measurement of the seals, there is a seal maker/supplier here in Vancouver B.C., that has always been able to supply me with just about any seal i am looking for or at least a decent usable substitue provided they have a sample. They are called Ryson seal, I will see if they have a website or get an address if you like.

Be very careful sourcing seals from seal dealers. Unless they know the exact material composition of the seal....do not use it. I have had several nearly catastrophic failures using seals from seal houses....back during my long term project to locate suitable seals for the clutch slave cylinders.

The problem is that our systems do not use a hydraulic fluid. We use glycol based fluids. There is not a hydraulic seal on this planet...a real hydraulic seal...that works well with auto brake fluids. Our rubber material is EPR. You must get seals made of correct rubber.
The problem is that a great many seal houses...and I have been through about 50 from coast to coast....do not actually know what many of their seals are made from. Only the best engineering based seal houses keep good track. Most of those stock no seals that fit.

Also...because of the pressures involved, peculiar lubrication and fluid flow charateristics....do not be tempted to use a seal that does not quite fit, with back up rings and filler o-rings. You cannot afford the experimentation. The problem with hydraulic seals is that they will work with brake fluid...seemingly well...until a certain mix of heat, pressure and water content. Then they fail almost instantly. Ray

[Milosak]

Rebuild in Czech republic... very good quality

[wildthings]

Rebuild in Czech republic... very good quality

You know a state side supplier? Or even a European one?

[ubercrap]

Czech Republic is in Europe unless I'm missing something...

[raygreenwood]

Looks very nice! Ray

[wildthings]

Czech Republic is in Europe unless I'm missing something...

Yes the Czech Republic is in Europe, while Taiwan is in Asia. I can buy stuff made in Taiwan right down the street in Anytown, USA, but where can I buy this part that is being rebuilt in the Czech Republic.

[raygreenwood]

Yes...its nice looking. They went to the trouble to paint or Cad palte it...and it has the check valve. I would buy one. Ray