So recently I put a LS6 in my 97 c5 corvette that formerly had the LS1. I got everything working, and the car function alright, except the clutch would stick when pushed all the way to the floor. Furthermore, it would also leak when pressed this far in. I replaced the clutch when doing the engine swap, using a stock GM LS7 clutch and flywheel along with a new slave cylinder for the 97 c5. Upon investigation, it appeared that the slave cylinder was over extending to disengage the clutch, which would cause it to leak.

After the horrid chore of removing the engine again (by dropping the k member and front suspension), I had access to the slave cylinder. It only had one thin shim behind it, because that is what seemed appropriate after measuring the system. I tried to measure the distance of the overextending, and decided to put one more shim behind the slave cylinder. Now, the clutch will not disengage at all, and is even more stiff.


TLDR: With only one thin shim behind the slave cylinder, the clutch system word work but overextend the slave cylinder and leak. Moreover, it would often stick because of the overextending.
With two shims behind the slave cylinder the clutch is extremely stiff and will not disengage the clutch at all.

Any advice on setting up these clutches?

 

From my expierence,,, a STOCK GM Clutch should NOT need any shims at all. I feel that the shims are your issue.

When you made the critical measurements, what were the finding?

If you over extended the pressure plate springs, you most likely need a new pressure plate also.

Bill

 

Well here is the thing, we measured the pressure plate distance and the height of the slave cylinder and tried to make them match.

When we first installed the clutch with the single shim, we got under the car to watch everything work. We were under the car (with the cover off of the bottom of the bell housing) one could see that with the single shim, the slave cylinder/throwout bearing would not really move the plate and start releasing the clutch until it engaged for about 6mm. This made us think everything was correct. With the single shim, the clutch would disengage in the middle of the pedal travel, if my memory is correct.

However, after we finished putting the car back together thinks started to change. We started the car, and everything was great. We then drove it about 2/10 of a mile, and everything was still great. A few days later, when we came back to do the finishing touches (putting on the hood and misc items) the clutch did not want to disengage properly. When getting in the car, we pushed the clutch in and it seemed to work, but then the pedal did not return. At this point, the I believe the clutch would still disengage, although it was sticking. We pushed the car out of the garage, and we could see that there was now fluid dripping from the bell housing when we would push the clutch. Furthermore, the clutch would now stick sometimes when pressed in.


After this we embarked on the miserable journey of gaining access to the clutch again. We took off the exhaust and torque tube cover, and opened up the bottom of the bell housing. The clutch would push in, but as the slave cylinder/ throwout bearing was getting close to the end of its travel, it would twist and start leaking. Once it twisted, it would start leaking and be stuck. We then removed everything to access the slave cylinder.

We added a shim that would remove the amount of travel associated with the twisting and leaking. The first shim was about 2mm thick, and the second was about 3mm thick, for a total of 5mm. This amount was less than the distance the system would travel before the pressure plate would release the clutch, so it made since that this would work.

Yet, the clutch will not disengage at all now, from any point in the clutch pedal's travel. \\



Any help is greatly appreciated. Also, is it easier to get the transaxle out in the back to access the slave cylinder? It takes me about 4-5 hours to remove and reinstall the slave cylinder going the front route (K member down with engine disconnected and pulled out of the way) I do not know the quickest process of removing the rear part of the drive train.

 

Jeff

The more shim that you add, the more that the slave will extend the throw out bearing into the pressure plate fingers.

What master cylinder are you running? Do you have the stock OEM master cylinder clutch peddle push rod installed??

Bill

 

After a few weeks of working on this in my spare time, here are my findings.(In response to the post above, we installed an aftermarket master cylinder that you can adjust at the pedal).

The current slave cylinder had a blown seal, even though it was brand new. It was also over extending and pushing the clutch plate into the flywheel.

I now have a new slave cylinder, but the ls7 clutch will not disengage anymore. You can get under the car, and see that the pressure plate is releasing pressure from the clutch disc, but the clutch will not easily move. When the pressure plate is pressed to the optimal position so that the clutch disc has the greatest amount of relief, it just bare is disengaging. It will almost kill the engine to have the car in gear with the clutch pressed in like this, which suggests the clutch is only barely disengaging.

I understand the ls7 clutch uses a SAC design, and is a Self Adjusting Clutch. The clutch would disengage with the leaking slave cylinder, but it will not disengage after the old slave cylinder broke and over extended. Is it possible that the Self Adjusting Clutch pressure plate is now out of adjustment? Or that the brake fluid from the bad slave cylinder has done something to the clutch?

On a side note, I have worked on a lot of clutch systems throughout my life, and I think the "shim" design for adjustments is the most ridiculous design ever.

 

QUOTE" "On a side note, I have worked on a lot of clutch systems throughout my life, and I think the "shim" design for adjustments is the most ridiculous design ever. "



The OEM GM C5 Clutch, "DID NOT" come from the factory with or used a SHIM for adjustment. Its was a factory preset air gap becaued all the clutch parts were carefully desiged to be bolted in and used without having to worry about fitment. .

IF,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, ,,,,,,,, You use something other than OEM for the clutch, pressure plate or any other clutch part, you are suppose to do the measurement/s to make sure you are still with in the OEM clutch stack-up height and not way out of spec, (too much extension or not enough). Most of the time if the measuremens are wrong, its not enough and you cant fully disengage the clutch disk and pressure plate. Thus the need for shim to make the slave cylinder move further into the bell housing.

If you dont need shim and add it, you move the slave/throwout bearing into the bell housing too far and over extend the fingers on the pressure plate.
Once you do that, its DONE, and you most likely need a new pressure plate.

Bill

 

I just got the car back together and all is well. The Self Adjusting Clutch mechanism (SAC) had adjusted all the way in on the pressure plate. It is actually possible to reset this out to its starting position with the clutch installed in a C5 corvette. Using the gap created by the clutch access plate on the bottom on the bell housing, you can have someone lightly press the clutch in from inside the car, while you use a screwdriver to move the adjuster inside the pressure plate back to its starting position. It is designed to ratchet in by itself over time, but you can manually push it back to its starting position while installed. Overall I am happy with the LS6 swap that uses the LS7 clutch.