While at VIR Monday, in my sc '02 Z06, I was going down the backstretch, in 4th gear under WOT, when the transmission started slipping(?). Car was revving but not accerlerating. I went to shift from 4th and the clutch wouldn't go in, like something was blocking it. I finally got in disengaged and out of 4th and it shifted fine thru the rest of the gears. I stayed out of 4th as much as possible, but sometimes it would run all the way up to the red-line in 4th with no problems. And once while going thru Roller Coaster section, not under heavy acceleration, it started slipping again. Is this a fluid issue? It felt like an auto tranny that was low on fluid, just curious if manual has that same issue. It was on the dyno Friday and no issues, no issues under WOT in 2nd, 3rd, 5th. I repl the clutch fluid Sunday, and did the WOT test is 6th on the way to work this morning, so it doesn't seem like a clutch issue. Fluid in tranny is stock as far as I know. Any thoughts?

 

That sounds like a clutch problem. There is no way you can have slip in a manual transmission gearbox

 

Sounds like you smoked the clutch. If anything is "slipping" it has to be the clutch in a manual gearbox.

 

Define smoking the clutch please. Down the backstretch I punch it from a start of ~45 mph in 3rd, shift to 4th. If it was the clutch, wouldn't it do it in other gears? As soon as I got it out of 4th, it shifted fine thru the other gears. I am hoping it is the clutch as it would be cheaper to fix.

 

DRIVE IT FOR A LITTLE MORE, AND PUT A LITTLE MORE PEDAL TO IT, IF THE CLUTCH, WITH TIME, IT WILL GET WORSE IN THE OTHER GEARS.

 

Makes sense. I am taking it thru some curves and hills on the way home today, to see if I can get it to do it again. May try switching fluid to the Synchromax to see if that helps. Thanks.

 

Hammered it thru some curves and hills in 4th yesterday and everything works. Couldn't get over 60, so I need to find a place where I can do 120!!!! Would $45 worth of Synchromax help or just be a waste?

 

It would make your wallet lighter by $45.00, which MIGHT make the car go faster ... other than that ...no benefit.

In your OP you describe the problem as a "slip" ..... the ONLY item in the drivetrain of a manual vehicle that can "slip" is the clutch. The transmission is either IN GEAR or OUT OF GEAR. In gear, two (or more) gears mesh and they CANNOT slip. OUT OF GEAR is a condition that you might command, as in putting the gearshift in the NEUTRAL position, or it could be because something has broken in the gearbox .... either way ... the engine is COMPLETELY disconnected from the drive wheels ... nothing "slips" there just is no connection.

The C5 has some "clutch issues" when you take the car to the track and REALLY beat on it. Commonly people report issues such as stepping on the clutch pedal and finding that it does not return when they lift their foot from the pedal ... it stays on the floor. Others have reported a "soft" pedal, when they step on it the clutch does not disengage properly. Both of these are mechanical issues with the hydraulic/mechanical parts of the clutch.

Also, some people can create a clutch problem ... I have a couple of times observed people who, after a shift, leave their foot on the clutch pedal. When asked why they do this, they usually say something like ... "I'm gonna make another shift in a second or two, so it is easier to just keep my left foot there on the pedal". The problem with doing that is that just as often I've seen them partially (and unknowingly) depressing the clutch pedal as they corner and try and use their feet to help them stay in the seat correctly (How many times has your leg felt like it was gonna punch through that door speaker screen ??).

Partially depressing the clutch pedal will create slip in the clutch, and worse, the slip generates HUGE amounts of heat that then ensure the clutch will slip even when your foot is not on the pedal. I try very hard to keep my left foot on the footrest on the far left of the footwell ALWAYS .... the ONLY time my left foot comes off the footrest is for a shift ... as soon as the shift is done, I get my left foot back on the footrest.

If the car is driving "normally" now, I'm guessing (let me emphasize GUESSING) that you overheated the clutch at the track. It could be your tecnique, it could be the dreaded C5 "weak clutch" getting you .... but here's what I would do if it is driving OK now ....

1) As Bugs Bunny would say ... "unlax" ... all is fine. For street driving your car will continue to give you many miles of smiles.

2) When you go to the track again ... think about where your feet are (along with those 48 thousand other things you're trying to think about at the same time) ... and if the clutch starts slipping again ... do a "cool down" lap .... put the car in, say, 4th gear, and just cruise for one full lap in that gear. Wave people by in the passing zones ... the idea is to let your clutch and other parts of the car cool off by not "working" them for a lap. I bet you'll find the car is fine after a lap doing that.

Enjoy ... I've heard nothing but good things about what a cool track VIR is ....

 

Thanks for the reply. There is a lot of info there. I probably do need to "un-lax". If it is a clutch problem, I guess it will only get worse and manifest itself more frequently and then I will know. I don't recall being one who "rides the clutch", but it is something I will pay attention to next time. If it happens next time at the track, the cool down time should tell a lot. Thanks.