onefastviking

Anyone have any clutch, really pressure plate, failures in a 996 or 986 where they end up damaging the transmission case ? I am trying to get some additional info to make sure I understand which parts are actually failing and why. Post or PM me.
Thanks in advance.

jakermc

Did you have another failure similar to the one at Nationals?

onefastviking

Not similar. Identical.
I'm pretty sure I know what is happening, just trying to add some more data points if any others are out there. I know the problem has happened to others I am just having a hard time finding someone to admit they have had an issue with it.

Premier Motorsp

The guy who bought my 996 racer had a pressure plate explode and cut the trans in half. Is that what happened to you?

On Cup cars that often happens when there is a mechanical overrev. Not saying you did that, but maybe worth thinking about.

Chris Cervelli
Spline Technologies

bobt993

Chris, how bad an over rev would that take?

onefastviking

Thanks for responding Chris.
Yep, thats it ! No over rev though. Just to be clear I am not the driver just builder/crew chief. My reasons for asking about this is to try to prevent it from occuring again, and to be able to modify the weak link to prevent it from happening again.

Thanks to the data in the car I know a fair amount of information about the failure on this, not just based on what the driver is telling me. While the data shows no mechanical over rev, I believe the failure is due to a very harsh deceleration. The clutch manufacturer also suggested mech. overrev. - once again I think that when you see the failed parts then you can demise harsh decell which most people guess mech overrev. and that is clearly a situation that could cause this to happen.

I am very curious what clutch disc, pp, and LSD (with % ramps) was in your car ? Also had it been on the dyno recently before your(or the new owners) pp exploded ?

I still havn't figured out if it's the drive straps that fail or the rivets that hold them on but I do know it is one of the two.

Thank you,
Viking

Pete Debusmann

I'm a friend of the guy that bought Chris's old car and was there when it exploded.It happened going into turn one at Daytona, so yes there was a lot of deccel. He didn't over rev it. It wasn't a stock clutch setup and I don't know what exactly it was, but Chris could probably tell you.

Pete

onefastviking

I can probably guess some of the things on Chris's car, LSD of high locking on decell, very aggressive clutch disc, lightweight flywheel. I wouldn't be surprised if it had been on a dyno recently also.
The failure part just isn't designed for the forces some of the cars can generate in a decell direction.

Premier Motorsp

I am not entirely sure what parts were in there when the failure occurred but I sold the car with a Cup diff, lightweight flywheel, and race clutch just as you describe.

I guess that the pressure plate explodes when it gets torqued strongly in 'wrong' direction (ie wheels driving engine) even if the engine is not overreved.

These cars just don't seem to be as tough as the older Porsches and GT3s are. It is really to bad, since they are cheap and plentiful, and the chassis is pretty damn nice.

Chris Cervelli
Spline Technologies

Larry Herman

Worried?



I think that it would have to be well over 8K for that to happen. Don't forget that ~8K IS the redline for cup cars.

cgomez

Not a 996 but a 987. I've had that failure, mostly caused by an overrev . It didnt immediately failed but after a few laps the gears were hard to engage. We kept going b/c it was a 9hr endurance race fighting for the overall lead and had 1hr to go..... and then the whole thing exploded and took the tranny case and engine with it.

drbooba1

What happens is the pressure ring which is the steel component the straps index moves off center due to either mechanical backhole or excessive RPM, usually a hell of a vibration occurs at the same time, next the straps break and the buzz saw occurs. The early Cup cars came equiped with the Sachs street strap set up of only 2 bands and they were a big problem, once at a cup car race I saw a team go through 3 pressure plates in one weekend event. You must use 3 straps even on the push type diaphragm set ups. Any hot rod clutch shop can change them for you. Sachs also has the correct Pressure Plate you just have to make sure they give it to you.

regards

Veloce Raptor

No matter how you look at it, "blowing a tranny" can never be a good thing.









Professional Racing and Driving Coach

Premier Motorsp

[QUOTE=Veloce Raptor;7330185]No matter how you look at it, "blowing a tranny" can never be a good thing.

Well, I guess you'd be the one who would know.

bobt993

Not me, but Darren is running a 996.