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clutch making the car shake?

Since my rebuild, the car has been running extremely well. I have noticed once MAJOR item which I don't like however.

If I am slipping the clutch slowly, the car starts to shake violently, like I'm going over the absolute worse cobble stone road in the world. If I release the clutch quickly, I have no issues and the car revs fine. When the car does shake, it's unbelievable how bad it is. The sound it makes and the bouncing are just horrendous.

Is that a misaligned clutch? IF so would it only do it when I'm trying to release the clutch slowly, or is maybe a bad flywheel too?
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1987 930
1956 Chevy 3100
2009 Subaru Forester
2003 KX250 X2(I like my toys!!)
Old 04-19-2010, 10:37 AM
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Could be used up motor mounts and worn clutch.

The big washer on top of the motor mount hides the condition of the rubber bushing below it... you don't know how bad they are until you remove them.

Some people wait till the motor falls out of the car.
Old 04-19-2010, 11:00 AM
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I've replaced the motor mounts, but not the transmission mounts, they looked good (as did my clutch and flywheel.
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1987 930
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2009 Subaru Forester
2003 KX250 X2(I like my toys!!)
Old 04-19-2010, 11:01 AM
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Mine was transmission mounts. Shuddered unbearably.

Drew
Old 04-19-2010, 12:58 PM
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Did you replace the pilot bearing "while you were in there"?
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Dave
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Old 04-19-2010, 01:00 PM
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Quote:
Originally Posted by WERK I View Post
Did you replace the pilot bearing "while you were in there"?
That's where my thoughts were going.....
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Mark H. 1987 930, GP White, Wevo shifter, Borla exhaust, stock everything else. The result of a massive Pelicanite good will fire recovery effort. Truely an open book, ready for the slippery slopes to modification.
Old 04-19-2010, 01:51 PM
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no, but I took it apart and greased the living life out of it. Ran nice and smooth after that, never had play before either.. I just wanted to re-grease it. I'll check my transmission mounts.
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1987 930
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Old 04-19-2010, 02:55 PM
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Ok, this is going to sound crazy, but . . .

When driving my 930 for the first time following reinstalling the engine, I experienced the exact same thing you describe (violent shaking when engaging the clutch) no amount of clutch adjustmen/fiddeling did anything to improve it . . . the owner of the shop that was helping me said he had experience with this problem and to replace the clutch cable with an authentic, Porsche 930 part (not an aftermarket bit) - I did, and this instantly cured the problem . . . strange thing about this was that the car DID NOT do this prior to droping the engine . . .

It is hard to describe, or understand, how the cable can cause this problem, but it has to do with the arch of the cable, and cable housing, in the area of the throttle bell crank . . . if the arch is not perfect, a mechanical resonance can occur when the clutch is engaged and trigger the violent shaking.

I was skeptical that simply replacing the clutch cable would solve the problem, but it did!
Old 04-19-2010, 03:02 PM
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Make sure you do not grease clutch release bearing. I did, and had the same issue as you. Cleaned the release bearing, and shaft, now it is smooth as butter.

Could also be the clutch cable. Something is holding the clutch back from the flywheel. That would explain why it is only happening when you let out slow. If you let out fast, the spring in the clutch is snapping it back in place.
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Old 04-20-2010, 06:47 PM
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You didn't mention what type of clutch, flywheel or pressure plate that you have?

Start with adjusting the Bowden tube, this must have the correct bend in it or you will get this problem. The tube keeps tension on the clutch as the engine twists, if not set right then as the engine twists in its mounts the clutch releases, the engine settles back and it grabs again, rinse repeat, and you end up with a bucking bronco.
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Old 04-20-2010, 11:47 PM
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I can't imagine why greasing the bearing is a bad thing.

David, you have an interesting point. Although I'm not certain what the Bowden tube is? Is that the tube that goes over the throttle linkage shaft sticking out from the transmission?

I had some issues initially with that and a sticking throttle (only slightly), so I moved things around so it didn't touch the linkage anymore.
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Old 04-21-2010, 06:24 AM
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not sure if his applies to a 930, though I would think it would. Contamination of the clutch disk can lead to shudder. You may notice it more in reverse than in first gear. For example, getting grease or oil on the clutch disk - or overheating and warping the pressure plate of flywheel - may not be a realistic scenario...
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Old 04-21-2010, 12:18 PM
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The Bowden tube is essentially the sheath which the clutch cable goes through (the black part). It has to have the correct tension on it to work correctly. It should arch up over the throttle linkage. The bowden tube works like a spring on the cable. When the clutch engages the torque twists the engine and transmission in its mounts (thats why old mounts can cause this problem, they allow too much twist). What the Bowden tube does is; it keeps the cable the same length as the engine twists. If there is not enough bow in the Bowden tube then it will do nothing to assist with this condition. Think about it like this, if the engine twists it will relieve tension on the clutch cable, and it will disengage, the engine twists back, the cable tightens and it grabs again, this happens in a fraction of a second, before your foot has even changed position on the pedal. So then it pulses on and off and the car bucks. The Bowden tube is designed to keep a steady tension on the cable as the engine moves on its mounts. Other contributing factors are a dirty disc, uneven flywheel or pressure plate.
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Old 04-21-2010, 12:35 PM
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ok, I'll check all of that later tonight. I think you're onto something. maybe it's time for a new clutch cable if it's shot (like some of the earlier comments).
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1987 930
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2003 KX250 X2(I like my toys!!)
Old 04-21-2010, 01:31 PM
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ccording to my wrench, a high performance will do it too. Necessary if yoy have a modded motor.
Old 04-21-2010, 10:41 PM
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Update

Those of you who brought me to look at the clutch cable were bang on. David, I checked the play in my cable and found that my clutch cable itself wasn't tight enough. I snugged it up at the transmission end about .5cm and voila... no more bucking bronco (that's pretty much what it felt like).

Thank you for pointing me in that direction, I would have never guessed that at all.

Car runs as smooth as it did before.

Thanks.
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Old 04-23-2010, 04:59 PM
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