-=Jeff=-

I read this a couple times, if the T-Out bearing is bottoming out on the engagement of the clutch I would not think it would cause an issue as the facing with the ears on the T-out does not spin.

What happens if you push clutch in part way?

desertmike1

Or, there is so much force being exerted on the Clutch release bearing that; it is trying to lock up, and put rotational force's across the Release "Fork" which happens to be stationary.

I'm Also thinking that the Slave Push Rod travel verse's the Diagram travel don't match.. or the Release Bearing has Crapped!

1985 Corvette

All the parts are new, but you may have a point on the clutch slave. It's a new cast iron piece but I was very paranoid about making sure the pushrod got into the divet on the fork as I was putting it in place. Doing it by hand, I had to muscle it on there due to fighting the hydraulic action. I remember being so happy I threaded the nuts on to hold the slave on, I may not have fully torqued them down and maybe it's allowing deflection.

I'll crawl under it this weekend and check those nuts that hold it on and make sure they are torqued down fully. Anyone know the sized deep socket for them? Thanks for bouncing all the ideas around, guys. It's a big help. Already preparing myself for the trans removal if it has to come to that....

I'll try to find the receipt for the clutch slave for the part number but is it possible the pushrod is too long?

bjankuski

If the parts are not correct or are installed incorrectly and the throughout bearing gets pressed against the rotating clutch assembly that stops the travel before the clutch pedal hits the floor it could apply high force to the crankshaft which would apply high force to the thrust bearing. This may be why the rpm drops. Without knowing what is going on that is about the only reason I can come up with a drop in rpm when the clutch is depressed.

-=Jeff=-

Good Point makes more sense now

Deakins

I would get underneath the car and listen with a stethoscope to see if I could detect anything funky going on inside the bell housing. In all honesty it sounds like a mechanical issue associated with the clutch and as much as it sucks I would pull it back apart before any parts get tore up beyond use. Just my .02

1985 Corvette

Figured I would post an update on this issue and it looks to be metal on metal contact inside the bellhousing. It sounds like the clutch fork is contacting the pressure plate at the last 1/4''-1/2'' of allowable pedal travel. I can feel it through the clutch pedal and the more I push down, the more metallic the noise and stronger the feedback through the pedal. The good news is it doesn't happen until the pedal is 1/4" or so from bottoming out against the bracket the clutch slave bolts to on the firewall. All gears are accessible with no grinding or other audible issues, or feedback trough pedal/shifter. There is also no rpm drop during most of the pedal travel.

The bad news is....well...it's happening at any point in the travel range of the pedal, even if 3/4 of pedal travel is perfect, that last 1/4 will bug me. I have been trading some emails with ZF Doc, and I'm waiting to hear back after reporting my recent finding. Already preparing myself for the inevitable advice of removing the transmission again. For the small distance involved, I would love to do a clutch pedal stop in the meantime.

SuperL98

If you truly think that the slave cylinder is pushing to far in, keep in mind that the motion ratio of pedal travel to slave cylinder travel is huge, so if it's only the last inch of pedal travel it's not very much slave cylinder motion.
On my 1988 its 7 3/8 inch of pedal travel to .70 inches slave cylinder travel, or about 10.5 to 1.
Instead of putting a stop on the pedal, try using a pair of washers to space the slave cylinder off the bell-housing.
A 0.10 inch washer would equal about an inch of pedal travel.
If it works you can try thinner washers to fine tune it.

ghoastrider1

congrats on finding the problem . Keep us updated.

desertmike1

Now your getting somewhere, and there is about a 99.95 chance you'll be pulling the Tranny..

1985 Corvette

Just wanted to do a little follow up that after much drinking of beer and reluctant glaring at the Vette, I dropped the ZF out but called it a day once it was safely on the floor. After sweating all day, didn't have the patience to dig into the bellhousing contents but that is coming this week or next weekend.

I only want to do this install once more and finally move on to actually enjoying the car, so I've got some concerns:

1) The car still has the tires on it but the car has been lifted up thanks to wood blocks I made for all four tires. I plan to jack the car up a bit so that it will rest on jack stands only, while the tires get stacked up and set aside. The car will sit at this point for a few months up high, but if I let it stay as is, how long before the tires flat spot from resting on the same section while on car? Brand new rubber I put on all four wheels not even two weeks ago.

2) Assuming clutch kit/flywheel combo is incorrect, how hard is this going to be to work with spec? Parts have 0 highway miles on them and have only been used to back car out of garage and drive back in. Had the kit since January 2014. Originally, I got it right before Christmas of 2013 but spec sent me the wrong clutch disk. They then sent me the supposedly correct sprung hub disk and then a few weeks later sent another one. In good faith (see stupidity), I contacted them on the extra disk and shipped that one back. Hopefully this doesn't end up being no good deed goes unpunished and I'm out in the cold on a $700 kit.

1985 Corvette

Here are some pics of the carnage. Also a few pics of the numbers I found stamped on the pressure plate. Any way to check these?







I found Dr. Huxtable's old thread with a similar issue but his problem ended up being a ZR-1 clutch fork pivot stud. I'm %99.9 it's not a ZR pivot stud in mine but I'll be checking it again. Also in the first pic, the wear pattern that has removed the blue paint off the pressure plate is not even....is this cause for concern or am I looking too far into it?

-=Jeff=-

Pictures if the stud? Not sure I would worry about the wear just yet. Find thenroot of the problem and then figire it out from there

rocco16

That wear is NOT normal.
You either have an/some incorrect part(s), or the installation was not correct.

1985 Corvette

Rocco, I'm aware there should be 0 contact but was curious why the wipe pattern was not evenly spread across the plate surface. But, as you said, could have been user error on installation. However, considering spec sent me a solid hub when I specified sprung hung Stage 3+ kit, sent me the seemingly correct sprung hub.....which had the sprung hub side labeled to face the transmission, then sent me ANOTHER sprung hub a week later, I won't rule out incorrect parts either.

I'll take the pivot stud out tonight for pictures and I may get the plate and disk off for pics as well. I believe I left the stickers on the disk, so I'll try to get pics of that as well. There was a pool of oil in the bottom of the bellhousing but I do not think it was from the rear main seal but oil leaking from the rear of the engine up top somewhere that was getting between the bellhousing and block mating surface and just happened to drip onto the main seal housing.

-=Jeff=-

measure the ZR-1 pivot stud, also if there is no locking bolt on the pivot stud, that might indicate a Zr-1 stud, modded to fit

Edit.. Pivot stud lengths:

The ZF6 L98/LT1 pivot stud is 3/4" tall
The ZF6 LT5 (ZR1) pivot stud is 1-1/16" tall, 5/16" longer

1985 Corvette

Hi Jeff, I'll take a look at it this evening, but the stud does use a retainer and I'm fairly positive it's the shorter, fatter pivot stud but it did have some decent wear into it on one side. The bellhousing is a magnesium version, I believe and I did have the metal spacers in place on the engine-to-bellhousing surface and the bellhousing-to-transmission mating surface, as specified for the mag housing.

1lndonr

Wow! I have installed clutches in Chevies, Chevy trucks, MG's , Jaguars, Dodges, Fords, and lots of other cars, and the raised spring side always, always goes to the transmission. If the plate is reversed you will get a false engagement when the raised spring housing contacts the flywheel and the car will move. The engagement is just the spring housing and not the clutch itself. The drag is from pushing the pressure plate actually pushes the springs harder against the flywheel and binds up. You can get the trans in gear because of slip and synchronisers.

Did you try the disc into the pressure plate when they were on the bench? When they are mated to the flywheel the weight of the assembly makes it hard to start everything into place and can be deceiving. Hope this helps.

tgurnick

Oh boy... I just caught up on this entire thread and am instantly interested in this because I remember selling you a pivot stud and fork awhile back.

The bellhousing I bought complete with fork/stud was an LT1 magnesium housing. I hope hope hope these aren't the parts at fault but it appears they're involved...

1985 Corvette

The way the kit is set up, there was only one way for it to go together. The sprung hub on the disc is about an inch or so tall. That side was labeled the transmission side...however, if I tried to mount the pressure plate to the flywheel in this configuration, the pressure plate mating surface was a good inch away from the flywheel. The single mass flywheel I have has a dished recess made just larger than the circumference of the sprung hub...which when in perfectly with room to spare. With the disc oriented like this, the pressure plate mounted perfectly and bolted up.

I will add that in this configuration, I'm staring at a sticker on the disc that says "flywheel side". But I chalk that up to someone put the stickers on the wrong side of the disc....there is no way it would fit flipped over following the stickers. Which leads me to wonder with the wrong parts shipped the first time and then the stickers on the wrong side, it's probably a good bet that I got a flywheel that is probably a little too thick or an incorrect pressure plate.



No worries, Tgurnick. I wouldn't say the parts you sent me are the issue but that's a risk I take purchasing used parts. The pivot stud has a noticeable groove worn into it from the fork from use but that comes with the territory. At this point I will be purchasing a new one from a gentleman in IA who still machines them to spec. Also, ZF Doc sent me a visual guide to mark on the fork and check with a straight edge for any possibility of a bent fork but this is a stout piece and it did not appear bent from eyeballing it.