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Clutch problems

dmd

Well-known member
Joined
May 18, 2005
Messages
156
Location
Seattle WA
Corvette
Supercharged LS6 6-speed Z06 Roadster
SANY0070.JPG


The clutch on my '96 LT4 has been getting progressively worse for the past few years, and now it's gotten bad enough that I think it's about time to think seriously about how I'm going to fix it. It'll hold for normal driving and while it's cold, but after it has gotten warmed up it'll slip with prodigious throttle input on the top three gears. I bet if this were an LT1 it wouldn't even have this problem, it's just not up to the task for a strong LT4. I bought it at 126k and have driven it for another 25k like someone who knows how a clutch works, but it had been through a lot of previous owners and since it goes like stink I'm betting the clutch has been abused along the way. I doubt it is the original and I have no way to know what it's been replaced with.

I've done clutch jobs on transverse setups before, but this will be my first longitudinal. I'm aware of this being a dual-mass setup and that you're supposed to replace everything, but that seems excessive for my situation. In the past I've been able to clean up the flywheel with some fine sandpaper, air-powered polishing pads like what I use to clean up cylinder heads, and/or a rotary wire brush on a drill. In light of how minor my issue is, I think that a flywheel cleanup and a new clutch disc and/or pressure plate would take care of it.

Has anyone attempted to do a clutch job this way on a ZF before?

Thanks,
Dave D
 

92BlackVette

Well-known member
Joined
Nov 19, 2008
Messages
211
Location
Austin, TX
Corvette
1976 Black, 1992 Black coupe , 2003 Black Z06
The clutch on my '96 LT4 has been getting progressively worse for the past few years, and now it's gotten bad enough that I think it's about time to think seriously about how I'm going to fix it. It'll hold for normal driving and while it's cold, but after it has gotten warmed up it'll slip with prodigious throttle input on the top three gears. I bet if this were an LT1 it wouldn't even have this problem, it's just not up to the task for a strong LT4. I bought it at 126k and have driven it for another 25k like someone who knows how a clutch works, but it had been through a lot of previous owners and since it goes like stink I'm betting the clutch has been abused along the way. I doubt it is the original and I have no way to know what it's been replaced with.

I've done clutch jobs on transverse setups before, but this will be my first longitudinal. I'm aware of this being a dual-mass setup and that you're supposed to replace everything, but that seems excessive for my situation. In the past I've been able to clean up the flywheel with some fine sandpaper, air-powered polishing pads like what I use to clean up cylinder heads, and/or a rotary wire brush on a drill. In light of how minor my issue is, I think that a flywheel cleanup and a new clutch disc and/or pressure plate would take care of it.

Has anyone attempted to do a clutch job this way on a ZF before?

Thanks,
Dave D

If you decide to forego the flywheel replacement, you will get the tin can rattle as the OEM flywheel ages. I decided not to replace mine when I did my clutch, kind of wish I did! Do it yourself, save money and good luck; I did mine. I won't comment on the flywheel clean up because that is a given.

Changed clutch at 100K, currently have 151K, OEM Optispark/cap and rotor too.

My clutch would slip when I hit rain puddles right before I replaced it.:W
 

G Winter

Well-known member
Joined
Aug 21, 2004
Messages
2,177
Location
NW Iowa
Corvette
1990 red convert 6 sp
I wouldn't change clutch without flywheel change. What I learned about the flywheels is that they have lube in them for the bearings. Granted mine is the earlier flywheel which does not have a shield over the seal. Apparently the seal went out on mine allowing lube to get on the flywheel. Mine at first would only slip after everything got warmed up. I assume the lube thinned and leaked out when warm.
I have been hearing that the dual mass is no longer available so you might be forced to use a standard flywheel and clutch.The clutch in my 90 was not that old but the flywheel must not have been changed.
Having worked on other clutches before the change shouldn't be difficult for you. It is time consuming. Lots to take out of the way. The 6 speed is heavy, not something you can lift by hand to take out and reinstall.
A little word of caution, if you use a bronze pilot bushing do not apply any grease. I know, been there done that.
I think it is best to use the needle bearing if your shaft is smooth. If you want any pointers along the way just let me know.It is still fresh in my mind.

Glenn
 

dmd

Well-known member
Joined
May 18, 2005
Messages
156
Location
Seattle WA
Corvette
Supercharged LS6 6-speed Z06 Roadster
I have no complaints with my current flywheel, obviously it's the later design with the bearing seal and it hasn't got the rattles. It seems like overkill to replace it just to fix a slipping clutch. Rockauto lists two suppliers for the flywheel, Sachs and Dorman (the Help! people). $805 and $1098 respectively. The clutch set was $116.
 

dmd

Well-known member
Joined
May 18, 2005
Messages
156
Location
Seattle WA
Corvette
Supercharged LS6 6-speed Z06 Roadster
Glenn, can you give me the quick rundown of the procedure, and does it require an assistant?
 

G Winter

Well-known member
Joined
Aug 21, 2004
Messages
2,177
Location
NW Iowa
Corvette
1990 red convert 6 sp
Not if you can find a transmission jack. You do need tall jack stands if you aren't doing it on a hoist.Hard to do with a regular floor jack. Help taking it out and hanging it back in wouldn't be a bad idea, save a lot of time. I did it by myself twice.
I caution on using the old flywheel. slipping only when warm is kind of odd. Usually a clutch slips or it don't. Mine held fine cold at first.
I spent $1000 for both flywheel and clutch kit just over a yr ago but I see where I bought mine no longer has them.
Remove shift knob and other interior parts to gain access to the boot, unbolt it from trans.If you have a convertible the 20 bolts to take the X brace off are first. Drain transmission.Then place jack under trans. Remove C channel and drive shaft.You can actually get by with sliding C channel back.(best to unhook battery cable)
Remove dist cap and rotor if it is an L98 on LT1 not sure if there are other clearance problems. Remove clutch slave and tie up.Unhook all wires . Lower trans to get at the 5 bolts.
Now it gets fun, lower and slide back trans in stages. The shifter has to come out of the boot and clear body. Mine would only lower to have 1/2 in clearance between shifter and body.From there standard bell housing and clutch removal.
Glenn
:w

I neglected to mention the complete exhaust needs to come off. Right after the X brace.
 

Itshakes

Well-known member
Joined
Apr 5, 2007
Messages
86
Location
Sandwich, Illinois
Corvette
2013 Grand Sport 60th anniversary Coupe
'96 LT4 Clutch

I wouldn't change clutch without flywheel change. What I learned about the flywheels is that they have lube in them for the bearings. Granted mine is the earlier flywheel which does not have a shield over the seal. Apparently the seal went out on mine allowing lube to get on the flywheel. Mine at first would only slip after everything got warmed up. I assume the lube thinned and leaked out when warm.
I have been hearing that the dual mass is no longer available so you might be forced to use a standard flywheel and clutch.The clutch in my 90 was not that old but the flywheel must not have been changed.
Having worked on other clutches before the change shouldn't be difficult for you. It is time consuming. Lots to take out of the way. The 6 speed is heavy, not something you can lift by hand to take out and reinstall.
A little word of caution, if you use a bronze pilot bushing do not apply any grease. I know, been there done that.
I think it is best to use the needle bearing if your shaft is smooth. If you want any pointers along the way just let me know.It is still fresh in my mind.

Glenn


I agree--been there, done that. Save yourself from doing it twice. The flywheels are hard to find--I got my at the Dealership! Bite the bullet, and pay the price! You won't be sorry.
 

dmd

Well-known member
Joined
May 18, 2005
Messages
156
Location
Seattle WA
Corvette
Supercharged LS6 6-speed Z06 Roadster
Update

I know it's been quite a while since I initiated this thread, but as anyone who has done this sort of job knows, it takes a lot of coordination and planning to make it happen. I got the clutch on closeout at RockAuto in a Beck/Arnley box, but to my great satisfaction inside was a VALEO. With that part out of the way, next came the question of where to do it.

My friend's shop I would need to use for this was tied up until the LeMons race at Thunderhill last weekend and I couldn't really work on it until that was over. What an adventure it's been since then. It's going to be tough to get it back together as nearly every exhaust fastener broke.

But getting right to the point, I finally finished getting the trans and clutch out of the car, and I never could have guessed what went wrong. Of course, both the pressure plate and flywheel were badly burned. But the real surprise was the clutch disc itself.

First strange thing was that it actually looked pretty good. No burns, no shiny spots, and plenty of thickness before it got to the rivets. But on the flywheel side, it looked like an LP record: the outer 1/8" was shiny. I had a hunch of what this meant, and a straightedge confirmed it: the flywheel had warped into a concave, dish shape.

I will not be attempting to resurface it. Checking for a quality used part first then ordering one from RockAuto if nothing turns up.

I'll be posting pics later.
 

Itshakes

Well-known member
Joined
Apr 5, 2007
Messages
86
Location
Sandwich, Illinois
Corvette
2013 Grand Sport 60th anniversary Coupe
C4 Clutch/Flywheel

The clutch/flywheel in my car was the same way. It had been grabbing on the outer 2" of the flywheel. When the flywheel was removed, the "Dual Mass" part was shot. When you would move the flywheel in one direction the hub would stay in the fixed position, and when the flywheel was released, it would not spring back to center. I replaced the whole assembly-Clutch cover, disk, flywheel, throw-out bearing, pilot bearing. It was expensive, but now it works as new!! GM flywheel, Valeo clutch/disk, GM throw-out bearing, GM roller pilot bearing. When the bell housing was removed, there was evidence that the clutch fork was hitting on the clutch cover. The pivot ball was working it's way forward, and the fork was hitting the clutch cover, so we put in a new pivot ball, and lock bolt too.
 

dmd

Well-known member
Joined
May 18, 2005
Messages
156
Location
Seattle WA
Corvette
Supercharged LS6 6-speed Z06 Roadster
New clutch is in, I'm finished up to the bellhousing so far. I did find a good used flywheel and it cleaned up nicely. Due to breaking all the studs removing the exhaust, the compressor, ASR, AIR, plugs, wires, and coolant temp sensor all had to come out to remove the exhaust manifolds. I tried replacing them with LT1 units, but the collector flange is different and won't work, so I'm having the broken studs removed from the originals by a pro.

Transmission, c-channel and driveshaft goes back in tomorrow, then I'll put the exhaust back together.

I would be so pissed off if I could only bill 8 hours by the book on this job, it's a bear.
 

dmd

Well-known member
Joined
May 18, 2005
Messages
156
Location
Seattle WA
Corvette
Supercharged LS6 6-speed Z06 Roadster
The pilot bushing was also worn out and loose, I yanked it out with a slide hammer and replaced it with a needle bearing pilot that's a perfect fit on the input shaft. All my spark plugs were at .060, I'm regapping those to .050 where they're supposed to be. She'll be good as new when I'm done with all this, can't wait to see how she runs.
 

93Rubie

Well-known member
Joined
Jul 19, 2009
Messages
777
Location
PA
Corvette
1993 Ruby Red 40th Anniversary Coupe
How did you get the car so high on the jack stands? My floor jack doesn't go that high. Is it totally rock solid like that?

I'm guessing you had to raise the car in stages? duh?

What kind of floor jack you got?
 

dmd

Well-known member
Joined
May 18, 2005
Messages
156
Location
Seattle WA
Corvette
Supercharged LS6 6-speed Z06 Roadster
Using a 3-ton hi-lift jack from Harbor Freight with their transmission adapter. It wasn't too difficult, two stages and it was up. It's high enough that we can sit under it upright to see how to get the upper bolts in.
 

dmd

Well-known member
Joined
May 18, 2005
Messages
156
Location
Seattle WA
Corvette
Supercharged LS6 6-speed Z06 Roadster
Finished things up yesterday in an all-day marathon, and what an improvement! The clutch grabs almost immediately as I release it, and where the pedal used to feel numb, release late and gave zero feedback, now it feels tactile and predictable. The pilot bushing quieted down the noise, particularly when in N with the clutch out. And fresh 5W-30 smoothed out the shifts. It's like a new car!

We decided that the exhaust is the the most elaborately retained in the history of automotive manufacturing. 12 bolts and 14 studs to hold an exhaust on?! Seriously?

Also, did everyone else have SAE bolts going from the bellhousing to the block? Thought that was a little odd.
 

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