I need some help guys. My 67 SS Chevelle is running great now but my 68 RS Z/28 has been kicking my but for 5 years now with a vibration. It's the 302, M-22, w/a 4:10 12 bolt. Around 4 grand up it's vibratating bad. I've tried: new harmonic balancer, new center force clutch & press plate, rebuilt the M-22, balanced the flywheel & the drive shaft. Even took the rear end apart and checked everything. New water pump, clutch fan. Each gear acts the same: take of in 1st, rev up to 4 grand, vibs, shift to 2nd, smooth until I get to 4 grand. This motor used to spin up to 6500 smooth as silk. Could I have bent a rod or crank shaft? I don't remember ever hydrualicing the motor.

What about the pilot bearing in the center of the flywheel? Someone posted something a while back about having a badly worn pilot bearing that was causing them some vibration problems.

Other than that, you've just about covered all the bases as far as external components go. You might want to try running a compression check to check for a weak cylinder. A weak cylinder can feel just like vibration. If you have a weak valve spring on one cylinder, it may be dropping off when you go above 4000 RPM. Tearing the engine down is the last resort, but you may have a problem on the top end that's causing you to lose a cylinder at higher RPMs.

Thanks Randy, sounds resonable to me, I'll give it a go

Hi 67

My bad vibes came from the drive shaft angle.

Jim