I spent a good deal of time last night reviewing all of the posts concerning clutch and hydraulic system problems.

My 04 ZO6 with 7K miles is back at the dealer for its second clutch replacement in 1500 miles. Service order from last work seems to indicate that the slave cylinder was replaced along with the clutch pressure plate, disc and flywheel.

Only ran 1500 miles and according to the dealer clutch is shot again. Problem was/is that it would not disengage and was engaged with the pedal only about 1" or so from the floor.

I haven't even driven the car hard. Only a few short bursts up to about 60 or 70 MPH (Maybe that is the problem??).

In the threads concerning the slave cylinder and hydraulics there was a good deal of discussion concerning DOT 3 versus DOT 4 used in the new 06 - ZO6. My main question is has anyone used synthetic fluid? It is DOT 5 and will stand quite a bit more heat. I have used this fluid in my Austin Healey both brakes and clutch for about 15 years. I do flush it out every so often because the synthetic fluid will not absorb water. I am thinking about putting that in my car when I get it back.

One other thing is the adjustment to the pressure plate as explained in the shop manual. Anyone done that and if so did it help any?

Apparently both the dealer and GM are scratching their heads concerning my clutch. Dealer has had the car for a week now and still no end in sight.

Thanks - The Forum is a great resource for a novice Corvette guy like me.

 

Hi Bob -

Well, there are a few of us scratching our collective heads reagrding the Z06 clutches....

Mine had the "stays to the floor" problem and the dealer replaced the slave and throwout, and about 5k miles later the problem was back.

I read Ranger's post about sucking the fluid out of the master cylinder with a turkey injector syringe and refilling it to keep the fluid fresh.

This has helped out tremendously, although the pedal still gets "numb" when I run her up to 6500rpm a few times.

Rodney at RPM seemed to think the problem was with the clutch master cyllinder and that a McCleod unit would help.

BTW - DOT 3 and DOT 4 are compatible, DOT 5 is not comaptible.

I use Prestone synthetic DOT 4.

The DOT rating is a measure of the boiling point as I understand it.

best regards -

mqqn

 

I had nothing but good experiences with my LS6 clutches, when they are properly installed.

Keys to that experience were:
(1) keeping the clutch fluid fresh, that should be an ongoing procedure, not just a few times.
(2) don't slip the clutch excessively on launch; pedal all the way out within 4'-8' of forward movement.

On the last clutch install on my 2002 before selling it, I had the installer make the adjustment of the pressure plate to ensure the engagement point was at mid-point of clutch travel. The procedure is laid out in the shop manual. It turned out fine. I didn't want the engagement near the floor.

Ranger

 

Thanks for the information. I will be on the lookout for Prestone Dot 4 Synthetic.

I think that when I get the car back (whenever that is). I will put it up on my lift and do the pressure plate adjustment. I prefer that the clutch release near the top. That is the way I "used" to set my clutches in the past (when we did that sort of thing mechanically).

I am afraid that GM is still mulling over my problems. I hope that they will replace everything this time and then I have a good start from there. I think that if it happens again I will just bit the bullett and put in a good aftermarket clutch. Got any recommendations??

 

Bob, what are the symptoms of the woes of your first clutch and the replacement?

Your warranty should cover any clutch issue for 36/36, unless they tag its woes to racing...which Chevy seldom tries to do.

If your car is less than 380 rwhp, the LS6 clutch is highly reliable if the owner follows the advice in my post #3 above.

I do have some aftermarket clutch thoughts but I'd need more info and it's not yet clear that you'll need one.

Ranger

 

Hi Bob -

I lied to you -

I checked the fluid I am using and it is prestone dot 3 synthetic fluid....

I apologize.

But it is synthetic and has worked for me just fine - I am sure it is just keeping it clean that is the trick per Ranger, not the heat range it is desinged to withstand.

I bought this bottle at Wal-Mart.

best regards -

mqqn

 

although i have been a F-body guy (still searching for my vette ) i know that my clutch would stick when i was in the uppper RPMS..(car put down 428 to the wheels on the stock ls6 clutch) They said this was caused by not getting enough fluid caused by a restricition in the master.

Now, i have just started reading vette boards, so i don't know if this is an issue, but its worth a shot.


http://www.installuniversity.com/ins...r_cylinder.htm

 

Ranger - Bought the car in February 06 from Chevy dealer. The car was a one owner 04-ZO6 with 5600 miles. In perfect condition did not look like anyone had sat in the drivers seat.

I drove the car home (about 120 miles) and parked it in the garage. Been several years since I had driven a stick with this much power, so I was not overly concerned that the clutch released right near the floor. I thought I could/would adjust it later. I also ordered shop manuals.

Few days went by (I was working away from home and at that time was still winter here in PA). When I got ready to back the car out of my garage I could not get the shifter to go into reverse without growling. Normal procedure is to put it is low gear to stop the gear train and then slip it into reverse. This did not work either. I was finally able to get the clutch to release and then when I started driving it, the cursed skip shift forced me to shift from first to forth. No way could this be done without grinding forth gear. I called the dealer and they said bring it back it.

I was still working and wife took care of it, driving back to Ohio. Dealer service guy rode with my wife and said definately had problems with clutch and/or tranny. They kept the car and then notified us that the clutch was bad - bent clutch forks?? Service order shows that they replaced the clutch, flywheel and pressure plate. Also shows entry for fluid, seal and a cylinder?

Wife picked up the car and drove it home. She said that it shifted much better. When I got to drive it a week or so later it was infact much better, but even after I installed a skip shift eliminator still have some problems with forth gear (I bought extended warranty for 5 years or 70K miles so I am not concerned.) When tranny warms up seems to be fine.

Took a couple of short road trips, but mostly just putted it around town with a few banzi blasts for good measure.

1500 miles after the first clutch, car was in garage for about 15 days due to going on vacation. When I tried to back it out of the garage - would not go into low or reverse. I finally had to shut off the engine and put it in reverse and then re-start. (Classic problem as pointed out by one of the forum guys.)

When I inspected the fluid - it looked like the photo from a couple of days later - pretty dark and a band of black guck around the top. Also looked like oil floating in the fluid due to big drops of somthing floating in there.

Called the dealer and they said to bring it back. I drove it back to Ohio - (boy was that a fun trip only using low and then jumping to 5th or 6th. tried to shift without using clutch, but didn't have much success darn new trannys anyways.) guys at the dealership were upset and in honesty they said they thought they had fixed it last time. (Maybe they forgot the hydraulics even though it shows up on the service order.)

They have had the car for a week and got e-mail just a few minutes ago that GM was buying off on the clutch and should have it back on Tuesday or Wednesday next week. When I get it home I will change out the fluid for the Prestone Synthetic. I may also put it up on the lift and make the pressure plate adjustment.

Forum is really a big help. I have spent as much time as I have available reading past threads. Just wish that I would have found the one about the black fluid before I got into clutch trouble again.

Been into cars for about 45 years, but this is the first Corvette for me. I love the car, but so far am not really happy with the clutch. Guess that it will be up to me to make sure that I don't have this problem again.

 

Thanks for the detailed explanation of the symptoms.

Seems, as you said, that they did not change out the hydraulics on the first clutch replacement. If they had, the fluid in the master cylinder reservoir would not have been nasty.

You also correctly recognized that it is normal for the tranny to be a bit balky on the shifts until the oil temp hits 100 degrees. But even at that, it shouldn't be hard to find reverse.

Sometimes the shifter cradle gets misaligned on reinstallation and moves the "shift pattern" too far left or right. That and the position of the pedal on engagement are things to check before you leave the dealer, when the 2d clutch replacement is complete.

I might suggest that you consider having them flush the tranny while they have the car. With fresh fluid, the tranny should shift smoothly once warmed up. If it doesn't, you know there is some pending tranny work forthcoming. They will probably charge you for the fluid and labor; I'd guess $125, but you might get it as a courtesy for the inconvenience of the 2d clutch.

Good that you got the GMPP. Not everyone is that thoughtful.

Once you scope out the car on pick-up, please post up and let us know how the dealer has done this time.

Ranger

 

Thanks for the info guys. I have and always will be a do-it-myself type guy. Worked in a Dodge dealership about 30 years ago and know how those places run.

Ranger - Sorry for the very very long explanation, but I am used to writing engineering inspection reports for turbine maintenance and usually have to go into detail such that the janitor could figure out what I wrote.

I will definately check out the car when I pick it up, but as far as I am concerned unless the tranny goes - I will probably take care of it myself from now on.

I was thinking about a new shifter anyways.

 

Bob,

I have had many of the same symptoms you mentioned. Although it made a difference for others, changing and/or bleeding fluid had absolutely no change in taking care of my problem. I did change to a McLeod master cylender. This helped in that I was always able to disengage the clutch at high rpm, but the pedal still got numb with most of the action taking place with the clutch right on the floor. I think this is because the McLead uses more fluid in its cylinder. Moving a greater volume of fluid also proportionally increases the pedal pressure (lower mechanical advantage).

I pulled out the new LS7 clutch and pressure plate I had recently installed and found that the pressure plate had gouges on the plate's surface. The clutch disk also had gouges. There were two rivets around the inner part of the clutch disk that appeared to be balancing rivets. They were bent looking. I think one of more additional rivets may have come loose and worked their way across the pressure plate. Something was amiss within this new factory combination. I installed another factory LS7 clutch pressure plate, going back to the factory LS6 master cylinder and the problem went away. The new clutch did not have the rivets that the earlier one had.

I can't tell you how nice it is to have a clutch that releases when it is supposed to again.

Chuck