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JFairman JFairman is offline
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Join Date: Jul 2006
Location: S. Florida
Posts: 7,223
Quote:
Originally Posted by mark houghton View Post
Thanks Jim. I guess it could be a CV joint, but they both seemed to be fine last time I had the motor out. Again, it's only when turning while backing up. I thought someone once mentioned that when turning and backing, the wheels are turning at different rpms (which would make sense because of the radius of the turn being different from the inner wheel to the outer wheel) and can result in such a noise if all isn't quite perfect within.
There's no way of knowing if a CV joint cage is cracked or deep grooves have worn in the inner and outer slots or races the balls run in without taking it apart and cleaning all the grease out with solvent. If there is a crack in the cage or a deep groove worn in the forward moving direction, then the ball can make a click or clunk while passing over it when the CV is torque loaded in the reverse moving direction.

The wheels turn at differnent speeds on all cars in forward or reverse unless there is a locked diferential in it.
In that case the inner tire will be forced to rotate faster over the pavement it's going over and it will skip and and make short skidding noises as it does it, especially if there is some dirt, sand, or gravel on the pavement.

Try pushing a race car with foot wide race slicks and a locked dif while turning the steering wheel... it takes several guys pushing on the car and it's difficult because the tires want to rotate at different speeds but the locker won't let them.

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Try pushing your car backwards in nuetral while the steering wheel is turned. That way the CV's are not loaded with torque to drive the car and the balls would be less likely to click or clunk if they roll over an unsmooth worn internal surface and the differential is just going along for the ride as the 4 wet clutch discs slip in 90 weight gear oil.

I don't know why anyone would bother with the expense or labor increasing the limited slip percentage in a street driven 930 LSD.
It makes no sense at all in a street car. It would increase or cause annoying chattering of the 4 clutch discs when making sharp turns slowly like from a stop sign and would just wear them out faster.

The ZF LSD slip rate raises considerably from static idle state with torque under acceleration and deceleration.
Old 12-30-2009, 01:41 PM
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