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Join Date: Feb 2008
Location: Marietta GA
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Is my clutch slipping?

When I recently rebuilt my transmission I replaced my clutch, pressure plate, and flywheel at the same time. The flywheel is stock and the clutch is a KEP organic, the pressure plate is a KEP lightened unit. When I first got my car put back together I didn't get the best adjustment on the clutch and it started obviously slipping under high load in second and third gears, I then re-adjusted the clutch and it seemed to hook up great but now I am starting to have my doubts again.

If I hammer it in second it sometimes feels like it takes a long time to run through the gear and the acceleration doesn't exactly blow me away. Other times it seems ok and it has even spun the tires in second after the adjustment although it was very cold and the road was dusty.

I know you guys won't be able to tell without riding in the car but I guess my question is did I ruin my clutch disk when it was slipping due to poor adjustment? If so what do think it is likely that I have damaged the other parts as well?

If it isn't wet tomorrow I will see if I can get a video to help illustrate what I am feeling.

Any opinions are welcome. The car makes about 400hp at the crank, the tires and gearing are stock.
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1987 GP White 930
1977 Ford Bronco

Last edited by willtel; 12-30-2009 at 05:30 PM..
Old 12-30-2009, 05:20 PM
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At 400 CHP, I wouldn't think you would overpower the clutch and tires. Sounds like you might have glazed the disk and/or flywheel.

Another thought is boost. How much are you putting out? Do you have a mech boost gauge? I found out I was spinning the tires because my wastegate was bad and boosting to who knows what.
Old 12-30-2009, 06:29 PM
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"If I hammer it in second it sometimes feels like it takes a long time to run through the gear and the acceleration doesn't exactly blow me away".


If it was slipping it would appear to run through the gear in no time and shoot up the revs but without accellerating the car as should

If the clutch was slipping in my opinion especially in a turbo charged 911 you will find that on boost it will slip quite severely and not just a little...An easy way to spot also is that it would also make your rev counter needle sweep up the revs inconsistantly and faster whilst slipping.
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Old 12-30-2009, 06:48 PM
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Quote:
Originally Posted by A930Rocket View Post
At 400 CHP, I wouldn't think you would overpower the clutch and tires. Sounds like you might have glazed the disk and/or flywheel.

Another thought is boost. How much are you putting out? Do you have a mech boost gauge? I found out I was spinning the tires because my wastegate was bad and boosting to who knows what.
I should mention that my tires are old Yokohama A540s that were stored for years in a Texas garage. They are starting to crack and don't offer much traction, I have new rubber but just need to get them mounted.

I believe my car has a 1 bar spring and I have an accurate digital boost gauge, I have seen it register 16psi at high RPM. Should I rebuild the WG?

Quote:
Originally Posted by stup View Post
"If I hammer it in second it sometimes feels like it takes a long time to run through the gear and the acceleration doesn't exactly blow me away".


If it was slipping it would appear to run through the gear in no time and shoot up the revs but without accellerating the car as should

If the clutch was slipping in my opinion especially in a turbo charged 911 you will find that on boost it will slip quite severely and not just a little...An easy way to spot also is that it would also make your rev counter needle sweep up the revs inconsistantly and faster whilst slipping.
I've had slipping clutches before in other vehicles so I'm familiar with the feeling and how RPM is affected. I do agree that once they break loose they seem to heat up and slip more as torque increases.

It may be in my head since I know it was slipping before the adjustment and all I could think about was not wanting to drop the motor again. I know I had some boost and intake leaks before the engine drop but I pulled the intake and replaced all the vacuum lines before it went back in so those should be corrected.
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Old 12-30-2009, 07:15 PM
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When I replaced mine, it quickly went out of adjustment and started slipping. A quick adjustment of the adjustment bolt put it right again. It's stayed in adjust for several miles now and hasn't slipped again.
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Old 12-31-2009, 01:07 PM
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An old fashion method to test the clutch is to raise the rear of the car and set it on jack stands, crank the car, apply the hand brake tight, put the car in first gear and release the clutch as usual, you might need a litle more throtle than normal take off... you'll find out pretty quick if the clutch is engaging or not by the smell and smoke without the rear wheels turning - if slipping; OR, the engine will cut off if the clutch is engaging properly.
Old 12-31-2009, 05:43 PM
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hey willtel. Was just inside and see your pictures (930)

The car is damn nice.
Old 01-01-2010, 03:35 AM
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After re-reading all this, it doesn't sound to me like clutch slipping. It's been my experience that when the clutches start to go, it isn't noticed so much as a general lack of power - but more catastrophic and obvious rpm increases with much diminished forward motion.

I wore out my stock clutch a few years ago, because it had much miles on it and I did the usual HP increasing mods. 2nd gear, or 3rd gear, floored and allowed to build from low rpms up...as soon as the torque curve and boost match up it would slip badly. For what it's worth: I'm not a clutch pro, just my experiences.

And on your boost level question: 16 psi spikes are not unheard of if you do indeed have a 1.0 bar spring. Do you see that 16psi sustained, or just momentary? Don't chase you tail until you know (1) that your boost gauge is accurate and (2) you've confirmed what spring is in your WG. So many things can contribute to spikes, and not just the WG.

By the way....nice color, nice year. We could park our cars side by side and get confused (other than the wheels, that is).
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Old 01-01-2010, 07:08 AM
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I don't remember seeing any adjuster on my clutch when I replaced mine about 5 years ago.
Its a hydraulic clutch, it should be self adjusting and I also have never had to touch it again.
20000km of hard use including trackdays.
All the best for 2010.
Old 01-05-2010, 07:41 AM
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Thanks for the insight guys, I double checked my adjustment on Saturday and went out and beat on the car some and the clutch is certainly not slipping.

I'm getting wheelspin at the top of first gear but 2nd and 3rd are pulling hard as hell. I love this car!
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Old 01-05-2010, 08:01 AM
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