I hate to just keep posting my own issues, but I'm having a hard time figuring this problem out ('85 4+3). I'm soon to be on my 4th clutch in 2 years, which has slipped since very early on. Break-in did not remedy the issue; on the contrary, driving it seemed to exacerbate the problem. Just to give a quick rundown of what has been replaced in the clutch system: slave cylinder, master cylinder, clutch fork, clutch disc (twice), pressure plate (twice), throw-out bearing (twice), and pilot bushing (twice). All at the same shop.

The first time the clutch was replaced, the bad fork was not... while I had no issues with slipping, my synchros ended up hurting for it so I got the fork and had the clutch replaced under warranty (by mechanic) because I heard a squeak that I figured was the beginnings of a bad TOB. Once this new clutch and new fork were in, the fluid was not changed. Maybe a hundred miles in, I had slipping whenever I had to do anything like merging that required subjecting the new clutch to a substantial--but not abusive--torque load. I chalked it up to being a new clutch and needing to be broken in like the last one did. However, there was a difference with this slipping in the sudden way it happened and that it was accompanied by a sound much like a cat hissing or paper tearing or maybe even a belt slipping. Soon after, it was bad enough that I could lay into the throttle going up a hill and see clutch smoke behind me. The smell was present every time.

It took a while to get my mechanic to take a look at it and I was driving the car almost daily in the meantime. I didn't usually put my foot down enough to recreate the issue, but it happened easily enough to the point where it was sometimes necessary. Then the problem suddenly grew worse one extremely rainy day when I had to park the car outside the shop. I got in the car to drive away and immediately noticed a change; the pedal pressure had changed, the engagement point was higher, the clutch seemed to slip just trying to drive 5-10 mph, and the pedal didn't seem to come up as far (though I can't verify that). After this happened, the car was nearly undriveable. Once the car, and consequently the clutch got warmed at that point, it would be like driving around with 50% pedal depression with low throttle input and like being in neutral with a bit more.

At this point I handed it over to the same mechanic hoping he'd do this one free after I paid for the last two bad clutch jobs. Friday, he had everything removed and showed me the clutch, saying he can't warranty it because the problem was my driving and that there were no other issues evident in the rest of the system. Well, I'd been telling him about the slippage for a while and my driving had been pretty easy on the clutch. So at this point I'm going to need to figure out what the problem is myself. I suggested bleeding the fluid because of the sudden pressure change, and I think that could be the issue despite the fact that they didn't try it. I guess it could also be pedal adjustment or clutch disc contamination, but I really can't diagnose it. The transmission is out and the car is taking up a lift, but I still don't know what part (if any) to order to fix the problem.

Anyone have any idea of what could be going on? Thanks for the time and sorry for the rambling post.

 

what kind of clutch? clutch disc material? I'm not really familiar with your year clutch but everything at least suggests that the throw out bearing was either wrong or adjusted wrong and preloaded the pressure plate, partially disengaging the clutch...which of course could also be misdiagnosed as "driver error" i.e. poor driving style (always blame the victim).

 

Has the flywheel been ground a lot? Every other part is new, the flywheel is the only piece of this puzzle we don't know about. If its too thin, (over ground) it is the answer.

 

It's an AC Delco clutch, so I'm guessing semi-metallic style disc. I can definitely see it being a bad throwout bearing based on the noise which sounded like spinning and partial contact between two surfaces.

I hate to be called that bad of a driver!

I knew I was forgetting something! It is an AC Delco unit (I believe) and was new with the first clutch, probably about 5,000 miles on it. So everything was new essentially.

 

I'm adding some pictures of the clutch itself in case it gives any clues as to what the problem is. I have to have a solution by today and I'd really appreciate any suggestions; otherwise, the 'vette will go back together without trans... this is really my only opportunity to fix it in the next two years







































Cushion springs seem properly waved




Not 100% sure I didnt accidentally do this while taking pictures

 

I just saw that the slave cylinder push rod ordered new from Zip and installed at the last clutch replacement was in a sorry state... not sure if this is noteworthy. Throwout bearing spins freely. Please let me know if there's anything else I should take pictures of or check out.




Fork tip<br/>




Slave cylinder end

 

Is anything else discolored, blued? I would be looking at the face of the flywheel and pressure plate, were those surfaces cleaned before assembly. Also, the fingers on the pressure plate and throw out bearing fork where the bearing rides and inspect the pilot shaft bearing. Was there any freeplay in the pedal before engaging and disengaging the clutch?

Gary

 

looks like date of mgr is 12-15?

Almost sounds like its a stacking issue but how if its Delco stuff. Receipts?

I dunno if it were me and this is round 3 hes blaming you and you paid 3 times Id be on the phone with Bureau of Automotive Repair filing a complaint that should get his attention along with small claims. Its cheap and fast, bet it doesnt even go there.
Driving style...bs.

If there was another problem he should have spotted it.
Maybe he forgot to test drive the car lol

Time to get all your money back and take it to another shop.

 

A (properly) machined flywheel will not cause this.
A bad TOB isn't likely to cause this either.

You need to break down the root cause; Hydraulics, mechanical actuation, or the clutch itself? What would cause a clutch to slip?
*Oil on the clutch (not present in your pics)
*A partially released clutch (actuation not releasing all the way)
*A faulty clutch; install, broken diaphragm etc.

The first thing *I* would check is, is the hydraulic system releasing all the way? If your pedal isn't returning all the way, the replenishing port won't be opened, and you could have pressure in the hyd line, holding the clutch partly released. I'd put the car up, get under and see if I could compress the slave. You should be able to by hand. If I could not...there is the problem. If I could, then with the slave compressed, (so the fork should be loose now), I'd try to move the fork and see if it hangs/binds in the limited travel that it would have at that point. If the slave were compressible and the fork seemed free, time to move on. I'd say the hydraulics/actuation system are fine.

The remaining checks would be inside the bell housing and the clutch itself. Not much other than the clutch that could cause this...other than the TOB binding on the input shaft sleeve. I've seen where this sleeve becomes so worn that the TOB gets cockeyed on it, and binds. This could happen, and prevent the TOB from coming back off the diaphragm fingers all the way. That would cause it to slip.

If that were in good order, I'd be scrutinizing the hell out of the pressure plate/spring etc. Something would have to be wrong in there.

FYI, a new clutch shouldn't slip under throttle/acceleration, "broken in" or not.


.

 

Thanks a lot for the replies, guys. This is really a huge help

I can't discern any discoloration or blue color to any of the components, though I have not seen the flywheel. I am not aware of any cleaning or lack thereof during the job, and it was foolish of me to not mention it beforehand. The fingers on the pressure plate seemed even and pretty unharmed in addition to the fork, although the push rod was damaged as pictured above. I'm assuming I should order a new one. All I can really attest to in terms of pedal action is that the engagement point became suddenly very high but otherwise seemed about normal before that.

Here are some pictures of the pressure plate as I could definitely be missing something.













I believe it is a 12/14/15 date of manufacture, which makes it very recent. I'm getting AC Delco to replace the kit under warranty--which is nice--but I'm afraid the same result will occur. The mechanic is someone I've known a long time and while it would be most prudent to do as you would, I really have to resolve the issue more amicably. But you're completely right and it's certainly a frustrating situation. I'm honestly not sure if he test drove it, but it took a long time to get the mechanic next door to confirm the issue when he couldn't drive it to diagnose the issue as slipping and that probably exacerbated the issue. At this point I just want him to install the clutch properly and carefully (I even bought the shop manual and handed it over to him before the first one) and not charge me an arm and a leg. If there's an issue after this, it's going straight to the Corvette specialty shop that just opened up not far away The car is only getting worse after bad repairs, and it kills me to let this happen. It would've been cheaper anyways.

Thank you for the thorough breakdown, Tom. I will be sure to follow your advice and take a closer look at the hydraulics. The first one I replaced slipped initially and stopped after a while, but I guess the fact that it wouldn't DISENGAGE might've had something to do with that!

Now I'm wondering if it's recommended that I replace the slave cylinder actuation rod (if that's what the damaged metal rod pictured is). Any insights?

 

nothing looks that bad but

(1) the crankshaft does have a pilot bearing?

(2) put a flat edge across the face of the pressure plate and see if it has warped (seen that)

(3) put a flat edge across the flywheel surface and confirm that it is flat

(4) with the flywheel installed, rotate the crank and with a dial indicator or feeler gages, confirm that there is no "wobble" at the outer edge of the flywheel; ( I saw a barely perceptible burr at the crankshaft / flywheel mounting surface throw a 0.040 inch wobble at the flywheel outer edge)

(5) check the end play of the crankshaft, a worn thrust bearing / crankshaft thrust surface can induce clutch engagement / disengagement issues (seen that one too)

 

Thanks for the tips. It seems that the flywheel could have somehow been the culprit. Debating ordering a replacement now as I'm unclear on whether the old one can be resurfaced, but at this point it might be worth it just for the peace of mind!

 

I can only offer one last bit of advice. Assemble the flywheel clutch throw out bearing, hydraulic slave, etc. Everything. Leave the clutch pilot tool in the disc and pilot bearing. Now, without the transmission installed (obviously) have someone operate the clutch pedal and observe that the clutch operates properly and disengages and engages like it should. If everything is right mechanically, this should tell the tale.

 

That's a fantastic idea. Just be careful though; the system could cycle visually, but not return all the way. That is why you need to, by hand, see if you can compress the slave when the pedal is released.

But having the trans out and watching the system function is a really good idea.

 

All of the posts have hit every angle that comes to mind, the only one that I see that has not been hit is if the Mechanic doing the install is not putting the throw out in correctly I once had a car come in with the Bearing installed in-between the Anti-rattle tang and fork.

All the photos that were shown I didn't see any real wear that would make the clutch slip, Worn yes Killed No.

Looking at the photo of the Push Rod being so Peened over like that makes feel that the problem is between the Plate fingers and slave, something is keeping the Throw Out bearing from totally Freewheeling during released times allowing the fork to Hammer the rod, weather it's a resting foot or a miss installed part, Throw Out put in Dry, Pinched slave Cylinder hose. something is keeping pressure on the Bearing and Pressure Plate.

 

Thanks; did it first time on my 96, after ZFdoc gave me some spec's for throwout bearing travel; saved me a lot of time and aggravation.

 

Sounds like a great idea to me! I'll have to head over there and check it out when the car is in the air tomorrow. I have a Sachs flywheel on the way, but in the meantime it's probably best to investigate as much as possible.

Makes sense, will do!

Thank you for the input! Would you say the slave push rod needs replacement? I'm just trying to visualize the whole thing really, but I think I understand what you're saying. I'll take a look at the slave cylinder hose, although the TOB itself seemed to spin pretty freely.

 

The TOB will probably spin well but if the whole unit itself Does Not totally release it could stick just enough to hold the fingers just a bit.
Before installing Lube up the New TOB slide it on the Transmission nose and Test fit it make sure it slides Freely, Than correctly install it in it's proper place. once the Trans is in take hold of the Clutch fork and Make sure the that there is a little Free Play that you can rock the TOB a little. you should be able to push the Slave cylinder back in to it's bore without to much effort pop the rod in (in some cases you may need to pull slave) Before totally Buttoning up car lower it step on the Clutch a few time, raise the car back up make sure the slave has released you should be able to twist or rattle the rod with a little bit of effort or be able to push the rod back into slave.

Yes I would replace the slave rod if I could find one and if and when you go looking make sure of the application I am Not saying that one from a Camaro or some other car might not work but make sure that it is the right part for your car. do your research verify the part Number

 

I'll be sure to do that and really appreciate the help. One last question: if I'm unable to get the push rod in a reasonable amount of time, would you consider it critical to install a new one (in theory or in practice)? Your endorsement of replacing it makes me lean heavily towards doing so (not to mention the worry factor), but it could be a matter of needing to vacate the car's current spot within the next couple of days. I think I'll be ordering a new reman unit tomorrow and see if I can get expedited shipping, but I figured I'd just throw in another stupid question while I had the attention of knowledgeable people

EDIT: Any opinions on this as a solution? Viable? https://www.corvetteforum.com/forums...post1585624677

 

Clean up the rod you have get the car back on the road, order up or find a replacement.
as for the home made rod link, no need not worth the effort to many donors out there and it's cheap new
http://www.ecklerscorvette.com/corve...1984-1988.html

I almost wonder if you even Have the right rod now if it is to long, with out having the car in front of me and seeing if the Slave is bottomed out in the bore (which it shouldn't be) when assembled you should be able push the slave plunger in and make the rod loose.