Heavy Vibration when downshifting (T56)

[dan_t]

Hi all, I've got a 96 Z28 that I'm starting to work through. Just done the Opti and got it running nice. I also had to replace the Clutch as the PO had a spring break on the friction disc.

I put a used but nice looking Stock OEM clutch.

I never got to drive this car before so I don't know if this issue was present before the new clutch etc.

Symptoms:
Real Harsh Vibration - Only on clutch engagement

-Most notable when downshifting at higher rpm's (engine braking etc)
-Also noticeable with big RPM changes upshifting ie - 6,000rpm in 2nd and then change straight to 5th with no throttle.
-Feels somewhat like "Axle Tramp" and feels either like the rear of the trans or the differential assy moving.
-Heal and Toe RPM matching hides the problem
-No Vibrations when Accelerating
-No Vibrations when Decelerating
-No vibrations or bad clutch engagement with low RPM driving

My instinct is that it feels like a worn out bushing. I might have expected that to also show up when decelerating using engine braking though - my issues is ONLY when I engage the clutch. Maybe its just more "shock" going through the drive line when the clutch engages or maybe its an issue with the clutch itself but casual driving is 100% smooth through all gears.

I've done a search and this doesn't seem to be a common issue. If anyone has had similar or if there is a known bushing that goes to give me a place to start looking I'd be greatly appreciated of your input!

Many thanks,
Dan

[cocobolo95]

Maybe the used clutch is the problem, or the problem was already there. I always change the pilot bushing when I change a clutch, but then again I also use new components. Because in areas like the clutch, looks are usually deceiving, as a clutch set that appears fine many times is not. If you change the bushing be sure the flywheel goes on in the same position, if there's more then one way it can go on. Also did you resurface the flywheel to get rid of the surface irregularities? I'm guessing no since you installed used components. Just like brake rotors, a surface with irregularities can cause all sorts of problems.