vibration at 3100 RPM

[wharlos]

OK I've read lots of threads about vibrations due to mis-timed balance shafts, bad clutches, pilot bearings, driveshaft bearings and transmission couplings, etc.

My 88 944 has a distinct vibration @3100 RPM with the clutch engaged. Its intensity increases under engine braking (very alarming when entering a corner in 2nd). It's still there (but not as intense) when cruising steady state down the highway in 5th.

I'm thinking that it has to relate to the driveshaft as the vibration is not there when I rev it with the clutch disengaged. My buddy, who I bought the car from replaced the clutch (proper diaphram spring - no rubber BS), and related release/ pilot bearings 10k ago so I don't think they would be the culprit.

Do I start with the driveshaft bearings and tranny coupling?

Any advice is appreciated.

[944 Ecology]

Before you go through all that, try running the car without the balance shaft belt first. That is the most likely culprit, and relatively easy to test.