Clutch problem - last run of the day

[Sly Dover]

The subject: 06, SC, AD installed and maintained, GWR exhaust, 3.2 pulley, 3-4 track days a year. So I'm hammer down on the last session of a track day, pulling out of a corner in 3rd. With no warning, unusual noise, or fluid, I've got no power in any gear. Could only limp around the track in 2nd at 10-20mph. Not enough power to get it on the trailer. Sounds like clutch to me, but isn't it unusual to not have any warning? If my mechanic says clutch is gone, I'd step up 1 level over stock. Would that be Exedy Stage 1? Other comments? thanks, Ed, MI

[Brian]

Indeed we expect clutch to slowly wear out, with more and more slip over time....not sudden failure though something could break and result in sudden failure. Exedy Stage 1 not enough for SC car, perhaps it was ACT Stage 1 which is enough. If clutch has been pulled the issue should be obvious, it's either toast or not.

[jboemler]

Clutch slipping is pretty obvious (engine speeds up but car doesn't), and not what I would have described as "no power". By your description, this sounds like an engine problem rather than a slipping clutch. Maybe you could clarify your description?

[Sly Dover]

thanks for the request for more details. The car had run flawless all day. I don't recall any incident that might have triggered the problem, but I was running it hard. Up until exiting that turn it had all the power and traction I could handle, then it was coasting regardless of peddle pressure. I shifted down and got just enough engagement between motor and wheels to limp back to the trailer- and get extra manpower to load it. Today, it engaged just enough to slowly roll back and forth in my garage. Some slight evidence of fluid under the master cylinder. Any chance I could have picked up/boiled an air bubble in the line that would prevent engagement of clutch? Just trying to eliminate simpler options before the clutch comes out. The car has 25,000 miles- half driven pretty hard- autocross and track days. thanks to all for the feedback. Will be couple weeks before it gets "cracked open to look". will update then.

[jboemler]

If the clutch is slipping, the engine will rev with good power all the way to redline -- it sounds powerful. Your description of no power and "limp" makes it sound otherwise.

So help me with my original question: does the engine spin up and sound healthy, but the car doesn't move; or does the engine bog down and not run with any power? These are VERY different things -- which is it?

Fluid under the master is never a good thing, and you should investigate that regardless of anything else. But loss of fluid would leave the clutch fully engaged, rather than disengaged.

There's little chance of clutch fluid boiling, since it's never close to a source of large amounts of heat. Also, clutches are less prone to effects of embedded air, since the pressures are low and flow is large (as opposed to brakes, where pressure is very high but flow is low).

Bottom line, hydraulic problems can make it impossible to disengage the clutch, but generally won't make it stay disengaged (or slip). If the clutch is slipping, it'll be a mechanical problem instead.

BUT, there's an exception to every rule. If your clutch pedal is adjusted too high, it will close off the port between the reservoir and the master cylinder. That permanently seals the hydraulic circuit, so that when the fluid heats up (not enough to boil), it expands and starts to release the clutch. It's easy to check, and worth doing. Just reach under the car and try to move the rod coming out of the clutch slave cylinder with your thumb. It'll take some stiff pressure, but you should be able to make it slowly move. If it's just stuck in place, then look to the pedal adjustment.

[Sly Dover]

Thanks JB for the feedback-sorry I didn't clarify the question. I can put it in any gear and rev the motor up normally to any rpm and with normal sound. Acts like it's in neutral. If I put it in second gear and rev just a bit-maybe 1-2000rpm it will move under power at 5-10 mph. Not enough engagement however to load on trailer by itself. I'm traveling after Sat, so can't reply to emails after Fri. Trying to do my homework before taking it to A.D. in couple weeks. Your comments sound like it's NOT likely a slave cylinder failure -the easy repair) -right? Fluid reservoir was full all day. Will be a couple weeks before we can crack it open to investigate further.
Ed

[jboemler]

Yeah, sounds like you're into pulling the clutch.