CNC Clutch Master Cylinder

[csx4017]

I would like some feed back on your experience with the CNC Master Cylinder when used in the clutch system. I presently have my third one installed. I have been chasing a clutch actuation failure mode. For the second time my clutch pedal has gone to the floor during street driving conditions. The first time I jumped on the Tilton hydraulic TOB as the issue. I replaced the 600 series with a 6000 series without firm technical rational. The TOB piston was not leaking. During the replacement the system would not bleed and the master was changed out. Went from an aluminum 3/4 to a steel 7/8........System bleed and we are back on the road. Second failure ( with exact non return of the pedal ) is in the process of being repaired.
History:
1) The CNC cylinders seal showed signs of damage ( nibbled edges )
2) 600 series Tilton did not leak
3) Do not have firm evidence that the 6000 series has leaked either
4) Thought about going external and eliminating the internal, again without firm evidence that it is the failure mode.
5) Waiting for the results of trouble shooting of CNC master.
6) Experts in the external, internal and Tremec TKO600 trans indicate that my issue is not with the Tilton TOB.
7) My long input shaft Tremec will not accept an external kit because the fork will have interference with the bellhousing/ pressure plate.

Present thoughts are to stay with the internal unless firm evidence shows leakage. If the internal is good then we have blown time and $$$ on overreacting and jumping to conclusions. Should the master cylinder prove bad then pulling the trans was wasted time.
Good news is the Kevlar clutch show no wear.............Any technical comments ??? Nick ???

[Tommy]

Nick,
I've had three of these CNC master cylinders in my car for about ten years: click here. They don't get much simpler than this. If the seal in your master cylinder is leaking, I'd look for signs the bore of the cylinder is becoming oblong rather than round. That can happen if the rod from the brake pedal to the master cylinder is not aligned properly, causing up/down or side forces each time the pedal is depressed.

[twobjshelbys]

Look for misalignment of the master to the slave. I went through this with my McLeod HTOB and after two of them switched the whole system to an external slave from someone here (been a while, can't remember, he's in MA, but it was a really sweet setup, and it was flawless after that).

[john chesnut]

Tommy is correct. The CNC units are reliable if properly aligned. I have an aluminum one for the clutch in my car and it's been trouble free. Misalignment will lead to premature failure. I've also seen the shaft length adjusted improperly. If's possible to adjust it so that to much of the rod is extended past the clevis at the pedal. If this is the case when the pedal is depressed it hits the rod and can bend it. A bent shaft will cause the misalignment. is the fluid in the reservoir clear or dirty and gritty?

It's been awhile since I had a McLeod set up. It was nothing but trouble. I think the supplier of the external set up might be Mike Forte. He's in MA and pretty sharp.

[mickmate]

Hey Rick, certainly alignment of master to linkage is worth looking at as the lads suggest. If it is showing nibbled edges on the seals that sounds like it is snagging something in the bore or overstroking and bottoming out on the end of the cylinder. Do you know it's not a heat problem causing hydraulic problems? What was your reason for changing master sizes? By putting the larger master you should displace more fluid (if you have a release problem) but it makes it harder to depress. I feel your pain as the HTOB are a SOB to get to but it doesn't sound like they are the problem. You should be able to go external if you want to and there is good reason to. It is just a matter of having the pivot points in the right place. There are some adjustable pivot points with set ups like Fortes but there are options with pivot hardware that come with a bell housing.

[csx4017]

I am going external. I put together a detailed response , but it failed to post. Will try again later.

[Tommy]

During the first two years I owned my car, I had the transmission out three times to solve problems with the HTOB. I replaced it with a clutch fork/external slave on a bracket I designed and built myself and I haven't had a problem with the clutch since. ... I think you'll be very happy with your decision.

[mickmate]

Hey Rick I can help you out with bits for an original style external clutch slave but be warned the clutch fork needs to be indexed for clearance on our frames. The window on the side also needs to be stretched out at the top.

[twobjshelbys]

Originally Posted by john chesnut

I think the supplier of the external set up might be Mike Forte. He's in MA and pretty sharp.

Yes, it was his setup I used. I went through two rebuilds from the CNC cylinder and they told me after the 2nd one that it was misaligned and that the HTOB was the root cause. Plus the HTOB itself had issues. I finally went with a new CNC 3/4" for the master and switched to Forte's external slave. Never a problem after that.

[csx4017]

Thanks for your responses.....Nick I appreciate your offer, but I am going with the Voss external kit. I went from a 3/4 to the 7/8 only because that is what I could find in a steel version ( at the time )...Voss has not finished checking out the CNC master for flow and pressure. Again, I am stating that I do not believe ( no technical rational ) that the Tilton HTOB was the cause of failure.

[dcdoug]

Originally Posted by mickmate

Hey Rick I can help you out with bits for an original style external clutch slave but be warned the clutch fork needs to be indexed for clearance on our frames. The window on the side also needs to be stretched out at the top.

I didn't have to index the window on my bell, but I did have to trim the fork and I do have a 1/8 shim on the driver's side motor mount to get the slave bracket to clear the frame, which probably gives me the extra clearance for the fork.

I have CNC master and external slave like Nick's set-up and am trouble free for 5,000+ miles.

[john chesnut]

I run a Chevy LS6 engine hooked up to a T56 Trans. This is the set up that's run in the Camero. It's the same HYD internal throw out used in the Vette as well. I read that it was tested for 1,000,000 cycles. I am using a CNC 3/4 MC and so far no problems.


Thinking about your problem more I do remember a clutch pedal not releasing because the rod was threaded to far into the clevis. It worked until the pedal was depressed just a little but further than usual. The pedal hit the extended part of the rod. It bent and became jammed between the clevis and the pedal. The pedal would not release. The fluid in the MC was dirty and gritty. I believe that the rod had been bent previous to the pedal not releasing. This caused a misalignment and the piston to wear on the cylinder. Eventually the seal would have failed.

An external set is great. But, you may have a simple problem with an easy fix.

[mickmate]

Hey Doug is yours a Ford bell? Lakewood is close to Ford position, Quiktime is way low and needs reindexing.

[csx4017]

As for rod end interference and bending, that has not been the issue. I have 2 CNC 3/4 masters siting on the bench, and the piston rods are straight and true. I am sending the info on fork re-indexing, cut out enlarging, on a QT BH, to Voss..........