Clutch Master Cylinder Failure

[Silk]

Well, in just over 10,000 miles I'm now on my fourth clutch master cylinder. Each time it fails, the fluid is black, indicating that the rubber seal on the piston has disintegrated. I've tried the following: leveling the pedal assembly; shortening the piston stroke; and using racing DOT 3 fluid (higher boiling point). I got a little better MPMC (miles per master cylinder) the last time after doing all this stuff (about 5,000 miles), but ultimately ended up with the same result. Spoke with the tech folks at Wilwood, and they were baffled and didn't have any other suggestions. I'm using the standard Wilwood (Girling) 3/4" master cylinder. Another Unique owner in the area is having the same problem.

Any ideas on this one? I'm now a real expert at swapping out master cylinders, but if I have to contort myself in the footwell one more time to R&R the circlip on the pin connecting the pedal and master cylinder rod, I'm going to have a head explosion! [xx(]

Gary
Unique FIA 351W

[eliminator]

Thought,

Are you boiling the fluid in the master cylinder and or lines with the header heat. Make a heat shield under the Cylinders, all of them. Little aluminum shelf like device with the high tech 1/16" insulation on header side use "sticky stuff" to attach. Then get some insulated sheathing that you can run over your lines. This would be good for all three. The heat could be cooking the seals. Material available from Summit.

Eliminator

[eliminator]

Thought,

Are you boiling the fluid in the master cylinder and or lines with the header heat. Make a heat shield under the Cylinders, all of them. Little aluminum shelf like device with the high tech 1/16" insulation on header side use "sticky stuff" to attach. Then get some insulated sheathing that you can run over your lines. This would be good for all three. The heat could be cooking the seals. Material available from Summit.

Eliminator

[terrybieritz]

Gary...

This isn't a direct answer and is only marginally relevant but I had issues with my Girling and finally replaced it. When I built my car the throw on the clutch lever seemed to be "just enough" to release the pressure plate. I had a Hayes "long" style pressure plate. I finally got it working but I just didn't think it was "right". I used silicone fluid from day one.

When I replaced my transmission recently the first clutch I bought was a CenterForce "diaphragm" pressure plate. Try as I could there wasn't enough throw in the clutch cylinder to release it. Two options were suggested. One...go back to the Long style pressure plate on the theory it requires less throw to release...and Two: replace the master clutch cylinder with one that has a larger bore...pushing more fluid which translates to more throw at the clutch cylinder.

I did them both. I bought a McLeod pressure plate, long style. I then bought a Tilton master cylinder with a 1 1/8" bore...the largest I could find. The combination did the trick! I can how adjust the lever to NOT have the throwout bearing riding the pressure plate constantly AND the clutch releases with minimal throw on the pedal.

The only down-side is it's a STIFF clutch! Oh well. It hooks up far better than the old combination. Maybe there's food for thought in my experience.

Terry

[terrybieritz]

Gary...

This isn't a direct answer and is only marginally relevant but I had issues with my Girling and finally replaced it. When I built my car the throw on the clutch lever seemed to be "just enough" to release the pressure plate. I had a Hayes "long" style pressure plate. I finally got it working but I just didn't think it was "right". I used silicone fluid from day one.

When I replaced my transmission recently the first clutch I bought was a CenterForce "diaphragm" pressure plate. Try as I could there wasn't enough throw in the clutch cylinder to release it. Two options were suggested. One...go back to the Long style pressure plate on the theory it requires less throw to release...and Two: replace the master clutch cylinder with one that has a larger bore...pushing more fluid which translates to more throw at the clutch cylinder.

I did them both. I bought a McLeod pressure plate, long style. I then bought a Tilton master cylinder with a 1 1/8" bore...the largest I could find. The combination did the trick! I can how adjust the lever to NOT have the throwout bearing riding the pressure plate constantly AND the clutch releases with minimal throw on the pedal.

The only down-side is it's a STIFF clutch! Oh well. It hooks up far better than the old combination. Maybe there's food for thought in my experience.

Terry

[Homewrecker]

Make sure your master cylinder pushes straight on the rod & clutch arm. The seals don't take much of a side force. Get the rod as straight as possible. Also, make sure that your clutch doesn't bottom out the cylinder in the relased position. Adjust the rod so that you can spin it when the clutch is released.
I don't know if this is a solution for you, but just some things to look for.

Dave Brouwer
Unique 427 with SA 428 & Toploader

[Homewrecker]

Make sure your master cylinder pushes straight on the rod & clutch arm. The seals don't take much of a side force. Get the rod as straight as possible. Also, make sure that your clutch doesn't bottom out the cylinder in the relased position. Adjust the rod so that you can spin it when the clutch is released.
I don't know if this is a solution for you, but just some things to look for.

Dave Brouwer
Unique 427 with SA 428 & Toploader

[Brent]

I agree with Eliminator on this one. I spoke to Butch Capps on this very item and he had trouble with the fluid boiling out of the master cylinder as well. I have even seen the fenders get so hot that the fiberglass mesh was showing through in the paint.

Good luck

Brent

[Brent]

I agree with Eliminator on this one. I spoke to Butch Capps on this very item and he had trouble with the fluid boiling out of the master cylinder as well. I have even seen the fenders get so hot that the fiberglass mesh was showing through in the paint.

Good luck

Brent

[Silk]

Thanks for the replies.

I have adjusted to make certain the rod is moving as straight as possible - and checked the stroke to make sure that it wasn't bottoming out.

As far as heat as a possible culprit, I haven't done anything so far other than switch to the higher boiling point fluid. No problems with the brake cylinders (with standard fluid) - and they're closer to the headers than the clutch master. But the metal line runing from the clutch master to the slave is a bit closer to heat sources than the brake lines, so I guess that might be an issue. I'll insulate the line and see if that cures it.

Thanks again for the thoughts.

Gary
Unique FIA 351W

[Silk]

Thanks for the replies.

I have adjusted to make certain the rod is moving as straight as possible - and checked the stroke to make sure that it wasn't bottoming out.

As far as heat as a possible culprit, I haven't done anything so far other than switch to the higher boiling point fluid. No problems with the brake cylinders (with standard fluid) - and they're closer to the headers than the clutch master. But the metal line runing from the clutch master to the slave is a bit closer to heat sources than the brake lines, so I guess that might be an issue. I'll insulate the line and see if that cures it.

Thanks again for the thoughts.

Gary
Unique FIA 351W

[rldunn7]

been there and had the same problems...the slave cylinder will..(repeat) will fail if you do not have some slack in the slave to clutch arm assembly. If you do not have enough slack, the failure will be caused by contact between the rubber and the back of the cylinder...usually a small slit/tear.

have you rebuilt the slave cylinder or just replaced it????
look at the parts they will tell you a lot...

One other thing to do is change the fluid regularly in the slave cylinder. Also, use the high temp fluid.

dickieboy7

[rldunn7]

been there and had the same problems...the slave cylinder will..(repeat) will fail if you do not have some slack in the slave to clutch arm assembly. If you do not have enough slack, the failure will be caused by contact between the rubber and the back of the cylinder...usually a small slit/tear.

have you rebuilt the slave cylinder or just replaced it????
look at the parts they will tell you a lot...

One other thing to do is change the fluid regularly in the slave cylinder. Also, use the high temp fluid.

dickieboy7

[davids2toys]

been there and had the same problems...the slave cylinder will..(repeat) will fail if you do not have some slack in the slave to clutch arm assembly. If you do not have enough slack, the failure will be caused by contact between the rubber and the back of the cylinder...usually a small slit/tear.

have you rebuilt the slave cylinder or just replaced it????
look at the parts they will tell you a lot...

One other thing to do is change the fluid regularly in the slave cylinder. Also, use the high temp fluid.

dickieboy7

Is this hi temp fluid you are refering to still dot 3, or are you talking dot4?
Also, what dio you think of vavoline syntech replacement for dot 4?