1994 LT1/ZF6
107k

yesterday the pedal felt a bit squishy to me but the trans shifted fine so I thought nothing of it and assumed it was my work shoes playing tricks on me. Now this morning the clutch pedal went to the floor with very very little effort. I didn't bother starting it up. I know there's a problem. Since prior to yesterday the clutch seemed fine I'm assuming this is a hydraulic issue.

My best guess right now is a failed slave cylinder - it looks like the original in the car. I'm hoping it is not the more expensive master cylinder.

I've seen somewhere online about a replacement slave that offers a hair more throw over the factory one to ensure full disengagement but I can't seem to find it again.

Thoughts?
-John

 

i would first diagnose the problem. check for leaks and check the level in the clutch master cylinder. as you stated, most commonly you'll see a faulty salve cylinder. most often they fail internally as the seal on the piston will shrink and will no longer hold pressure. the fluid will eventually leak past the boot and onto the ground. i know you don't want to hear this as its more money out of your wallet, but when replacing or rebuilding the slave cylinder, it always best to replace or rebuild the clutch master cylinder and replace the clutch hose all at the same time.

 

I appreciate the reply and will diagnose before replacing anything.

I have done some reading and see that it is not uncommon for the master cylinder to fail in such a way that fluid leaks into the interior/carpeting. There are no external leaks to the ground so if the reservoir is low I will suspect this. If the reservoir is full then the only real explanation is an internal seal failure.

Why is it necessary to replace the master cylinder if it is ok? Precaution or other reason?

I imagine that the only thing that can really go bad with either the master or slave is a failed seal. Are there rebuild kits readily available? Is it worth it to rebuild the slave cylinder or for the cost to just replace it?

I've read that many replacement units have an incorrectly (backwards) installed seal that can cause an issue. Still a problem or is this defect a thing of the past?

Any word on the slave cylinder that offers a bit of extra throw?

I planned on replacing the fluid. Can you power bleed the clutch hydraulic setup like you can with brakes? This is the kind of setup that has an external reservoir with a low pressure air source that forces fluid through the reservoir-->master-->out the slave bleeder.

 

Be sure to read this before getting new parts

http://zfdoc.com/CHS_Actuator_Seal_Fault.htm

CF thread
http://forums.corvetteforum.com/c4-t...sue-found.html

 

I want to rebuild both the master and slave rather than replace them but I can't find a rebuild kit for either locally. I have checked NAPA and the big chain stores (Autozone/Advanced) but no one seems to be able to get it.

Are rebuild kits available? If so where?

Edit: just moved the ecm out of the way and the reservoir is DRY. The interior carpeting is also dry and I have not noticed any stains in the driveway.... where did the fluid go! I'm going top fill it up, hopefully drive it over to my garage and then have a look underneath.

 

Here is what I did:

Filled reservoir up and pumped clutch like mad and the pedal came back. Not perfect but enough to make the 7 mile ride to the garage. Once there I got under the car and right away noticed that the bellhousing was wet where the slave cylinder bolts up. I unbolted the slave and sure enough the boot/rod are soaked in fluid. So bottom line is this looks like a slave cylinder failure.

This thing looks to crumby to bother rebuilding anyway. It has rust on it. Ordered one at parts store and will have it tomorrow. The brand is "Perfection Clutch" - do I need to take it apart to check for burrs and proper seal installation?

The master cylinder is staying as is for now. I'm going to flush it with a lot of clean brake fluid since the stuff in there is black and severely contaminated. In fact I can almost guarantee that degraded fluid was a major contributor to the failure.

 

Have the same problem now in mine.........damn thing (slave cylinder) only lasted 5 years and this car is not driven much at all....glad you started this thread......there were good threads above from the ZF doc's website........will pass this along to my mechanic....thanks all

 

You should absolutely disassemble the slave and inspect it. I've done a ton of them and every single one had crap in the bore. Not one was perfectly clean out of the box.

 

This has been an ongoing issue with my wife's '94 Vette. She is getting very good at re-filling the master cylinder herself.

We have found that the replacement slave cylinders do not last all that long........less than a year and they are getting hard to find. We are now keeping an extra one (or two) in stock and have also found that Summit Racing carries them. The slave cylinder from them seems to be standing up better than other ones we have used.......so far.

BTW, it is possible to refill the master cylinder without totally removing the ECM. Just remove the two or three small bolts (9/32 I believe) that hold the ECM to the plastic frame. Then you can slide the PCM out an inch or two to gain access to the master cylinder cap with your fingers and get it off. We use a small plastic funnel to master cylinder funnel. I also believe that this system is self-bleeding. Did this the last time we filled it and it worked like a charm.

 

Your slave cylinders are failing because the seal is installed backwards. You can take the slave apart and flip the seal over. If you do that, the slave should last a decade or so. Even the cheesy plastic ones should last quite awhile with the seal installed properly. The cast metal ones might last forever if the seal is installed properly.

 

Fellas:

I installed the new slave cylinder last night. Bled the clutch and all was well. Nice firm pedal and full release. The unit that I installed is far more robust than the one I removed. The flange on this thing is thick and it has a nice cast body. The one I removed had a thin sheetmetal flange/body. In fact when I bought the car one of the first things I did was bleed the clutch. With a helper pushing the pedal while I was under the car I could SEE the slave cylinder torquing around! No chance of that with this new one.

So like I said, last night all was well...

Now, this morning when I drove the car the clutch felt a little bit on the easy side to push. I am leary that it is leaking already. When I go to start it this evening I imagine I would have leaked most of the fluid.

I'm willing to bet the seal, as mentioned above, is install installed backwards. I attempted to take the cylinder apart before installation to inspect and clean but my snap ring pliers were too flimsy to remove the first ring. The pliers would twist rather than collapse the ring - so I installed as is. I suppose I'm the fool for not heeding all the warnings. Live and learn I guess.

Question, is the damage done? Or can I still take this thing apart, correct the hopefully backwards seal and be good to go? If the seal were backwards where would it leak? Would this be an internal leak allowing fluid to leak past the slave piston so it is not as effective, or would this be an external leak?

I'm long winded, I know. Sorry.

Thank you everyone!
John

 

jmgtp,

Thought I read that the cast ones (like your new one) didn't have the problem of the seal being installed backward.

Further, thought I read that trying to take apart the cast ones was not recommended and would likely damage the seal, making it not re-installable.

Regarding the softer pedal in the morning -- any chance it is just some of the air, which had gotten into lots of small air bubbles and has now joined together to make larger air bubbles which you can feel?

When your were bleeding, did you do the old fashion bleeding method? Afterwards, did you do the 30-50 variable speed pumps and then re-bleed? If not, suggest trying that and seeing if it remains constant the next morning -- before trying to disassemble/rebuild.

 

I couldn't get it to bleed the conventional way it would just be air - fluid wouldn't ever make it's way down to the slave.

I ended up comprssing the slave by hand, having some fill the reservoir while I held it compresses and then released so the slave would draw fluid in. I did this a few times - it was the only way I could get any kind of pedal. After that I loosened the slave bleedee, put a Jose on it and submergedthe other end in a bottle of brake fluid. I pumped the pedal on the theory that it should force air out and when I released it should draw fluid from the bottle. It seemed to work as he pedal became as good as before the problem and I had full release.

This mining he pedal felt a bit squishy. Still shifted okay. So either I do have a leak or I have some air accumulated. The level of fluid in the reservoir should help tell that story. I'll be at the car in about 20 mins and will find out...

 

Pedal is the same as this morning and fluid level looks ok. I think it is either a little air or all in my head. Clutch seems to release full - shifts ok. I'll bleed again but I think that it is probably ok.

 

My 94 exhibited almost identical symptons. I'm going to replace the slave and master and so I bought both from NAPA.

The master is cast, labeled "Made in China" and has a cheap "looking" reservoir with NO internal hat shaped moisture barrier.

Do's anyone know if this part is acceptable or should I take it back to NAPA and look for a higher quality one?

Also: Is it absolutely recommended to replace the line too? If yes, where is a good source? Ecklers list one for $178. Seems way to steep (like most Ecklers prices).

Thanks, Rich

 

If you don't like the looks of the new master cylinder, why don't you rebuild the old one. I rebuilt mine over 5 years ago and haven't had a problem and the kit was less than $20

 

Who sells the rebuild kits?