ukrbmw

Got the new car out to the track at VIR with PCA today. Absolutely amazing. I'm running DTC70s front and 60s rear, car is stock with T1 bars running on 315 square setup, which is great, except the left front rubs a bit.

Grip level is amazing, brakes after bed in were sick. On the back straight of VIR I can brake at 2 marker from 140 down and still had time left over (I wasn't pushing that hard on top end). Only car I couldn't get was a well driven ZR1 (pretty white one with carbon fiber wheels and some Hoosiers). Everything else fell victim to the Z. This was pretty funny since I'm used to driving a Spec E30, which typically gets passed by almost everything. Overall, couldn't be happier with the result. Next on the list is putting Traqmate and trying to get some lap times.

Only bad thing is something funky going on with the clutch. After 15-20 minutes of hard laps I could barely get it in to 3rd. No problems with upshifting, just on the downshift. I could let the car coast for a minute to cool off the clutch and then it would engage no problem. Felt like the clutch was fine, but something else was causing it to fail when it got hot. I'm sure this has happened to others and thought somebody would tell me. Car is still under warranty, but it would make it easier to deal with the dealer. Unless, of course, it is the clutch in which case I'll be paying for it.

crainholio

If upshifting is fine, and downshifts other than 3rd are fine, it's not likely clutch issues.

When mine stopped downshifting into 2nd, it was blocker rings.

I'd start by changing the trans fluid and flushing out the clutch hydraulic fluid before removing the trans, just to rule out the cheap and easy things.

drivinhard

welcome to the darkside, they are just a blast to drive

get some really high temp (and fresh) fluid in the hydraulics, when they get hot, they can not release 100%.

the best thing about the quartermaster clutch I put on is not the clutch, but the MUCH better (than stock) TOB hardware/hydraulics. Full release, EVERY time, at any flogging/heat level

also fresh fluid in the trans, the blocking rings work the best with fresh fluid

RaleighSS

With my z I had the ole dirty fluid in master issue where the clutch would stick to the floor when hot. I know that is not your symptom but I would think a fluid swap in the trans and trying to cycle fluid through that master may be the first steps.

71corv

Had the same problem today running in the blue group in my C5Z. Going into #1 went to down shift and clutch stayed on floor. Pulled off the track and after a short cool down was able to drive back to the paddock.Will try the suggestions already provided.

Gene

RaleighSS

Without a remote bleed kit bleeding the clutch can be tough .... Best bet is to put new fluid in res tnen pump till it dirty then change again 3-4-5 times

varkwso

fresh fluids are the best option. In the T1/ST2 car it was repaired when the clutch was bled (remote bleeds are a wonderful thing!)

Fluids in trans is also a good hail mary before puilling it....it works sometimes

ukrbmw

Thanks Mark - I tried resisting for over a year, but couldn't do it any more.

I did change the fluid in the reservoir twice and went a little longer on the second run before having trouble with 3rd again.
Gene - my clutch did the same - to the floor and can't get to 3rd, so I'd rev match and get it in gear and it popped back out a second or two later. I'll flush the fluid a couple of more times and transmission fluid will be next. I've been looking at the Tick bleeder kit, plus they are 20 minutes from my house. Just wondering if I should let my warranty run out before doing that.

Mark - I've been looking at clutch options. Problem is I still drive the car on the street and anything pretty aggressive gets to be a real PITA. Although after doing my first track day I'm finding myself searching classifieds for an ST2 Corvette...

Han Solo

You probably won't be able to duplicate the problem for warranty purposes and if you explain it only happens on the track, WELL?

Bleeding the clutch is a pain but not impossible. You just have to drop the exhaust and center plate to get at the bleeder. Hook a tygon hose up and let it gravity bleed till it runs clear then have someone step on the pedal a couple of times while closing the bleeder at the bottom of the pedal travel between pumps.

That turkey baster method won't get anything out past the master so don't waste your time. I did mine over and over till it stayed clear at the master and when I did the clutch I pushed the plunger in on the line to flush it before hooking up the new slave. Solid black fluid came out of the line and the old slave had solid black fluid in it.

varkwso

You can pick up the clutch with your toe when it sticks on the floor. We got pretty good with it...

kmagvette

The hydraulics on the C5Z let clutch dust get into the fluid. The easiest way to ensure that this does not ruin your track day is to replace the fluid. A bleed is the best way, but a serious PITA. I just suck the reservoir dry and refill. You can pump the pedal 50 times and repeat or just drive it for a few days and repeat. Continue the process until you no longer see any signs of dirt in the fluid.

To maintain, I just suck the fluid out and refill before every day on the track...no trouble in three years after my bout with the sticking pedal.

Carquest sells a cheap DOT4, Motul RBF600 seems to work well too. There always seems to be leftovers after a brake bleed, so that is what I feed the clutch with.

Flies Lo

This is good to know...so we can use something other than the magic GM "Clutch Fluid"...I like Motul, and I'm having my brake fliud flushed before my first time on the track with my new GS and Motul installed...I was going to do the suck/fill/pump/suck/refill/pump/suck till clean thing so I tried to get some of the clutch fluid from my local dealer; of course they didn't have any in stock...

I'm curious how clutch dust can get past seals that don't leak fluid...you guys certainly know a lot more about this than I do; I simply do not understand...

brkntrxn

Car to wager any times yet, Alex?


Inquiring minds and skinny wallets want to know......



-Kevin

kmagvette

There is a lot of debate as to whether or not the fluid is darkened due to clutch dust, water absorption, heat, etc. Apparently I subscribe to the dust theory. I googled around for a bit looking for the original article I read that formed the basis for my belief...couldn't find it. I did find this article which also identifies dust as the culprit. Clutch Care

No matter the cause, my experience has been that keeping the fluid fresh has prevented the low pedal problem from returning.

There are other opinions out there, so keep the salt shaker handy.

drivinhard

Here's some info from a ceramics engineer friend of mine that has build numerous ceramic ball bearing clutch release bearings, for various cars. I have run them on other cars but not the C5 (although we do have 2 of these in testing, on in a 900 hp C5, one in a TTA C5 here in the SE). On the bench, these run 40% cooler than a stock bearing.

"If the clutch fluid is clear then no need to inspect the bearing; we would suggest he continue to run it and see if it helps the fluid malaise issue effecting C5/C6. Again, we think this is a function of the large diameter output shaft needed to handle C5 levels of hp from the factory. This larger diameter pushed the diameter of the inner and outer races of the TOB outward - in turn increasing the rate at which the ***** are accelerated for a given shift at a given rpm. GM tries to address this by using extremely small bearing ***** (so that they can accelerate more readily). The C5's are the smallest we've seen in any production TOB. Hoever, if they can not accelerate fast enough to match engine rpm they will skid (slide, not roll). We suspect the ***** do skid especially in drag race/road race applications; this generates an enormous amount of heat directly adjacent to the slave cylinder, cooking the fluid. The ceramic rollng elements are 2/3rd lighter than the stock metallic elements, have a lower coefficent of friction (no microwelding like on all metal bearings), and have fatigue lives that will outlive the car itself."

Han Solo

My opinion is the dark fluid is due to rubber seal degradation. Many cars have the dark fluid that haven't been raced or driven aggressively. The fluid turns dark in any hydraulic brake or clutch system over time. The answer is just to flush the fluid. No need to over analyze it.

Jason

One other thing to check, especially on a car new to you, is the shifter bolts. I've seen them loose and others have too. Can really drive you crazy trying to figure out why your car will shift fine into some gears and hang into others.

varkwso

Been on that ride - good tip