ahspros

Have 86.5 Porsche 928 with automatic transmission and 81,000 miles. I had it in a Porsche shop to replace the timing belt, water pump and correct some vacuum leaks on the A/C system. The motor mounts look good and so do the transmission mounts. Went to pick it up and ran great for about 200 yards when a loud bang came from the motor and the car started shuddering. Took it back and found that screwdriver was left in the bottom of the fan shroud and was picked up by the fan. It broke a number of blades off the fan which caused the noise and shuddering. Replaced the fan but now has developed a hard vibration coming from the transmission. You can feel it through the seat, searing wheel, floor and any part of the car body. The vibration is in all gears and harder when under a light load. When driving at any rpm but not accelerating everything is smooth. The vibration is present only when accelerating. When not in gear motor is smooth at any rpm. The shop said that it's the clutches slipping, “sure it is “right”, in all gears?

Mrmerlin

Hello welcome to the board, can you please add more description to your post.
Where are you feeling the vibration in the seat?
through the pedals ?
from a noise you hear?
Have the motor mounts and the trans mounts ever been replaced?
Did the shop that you used have experience working on 928s?
So the HVAC system was worked on or was it the A/C system

Sapientoni

Are you sure it's the trans? In all gears could be a bent rim, possibly they took it out and drove it hard, twisting the drive shaft. It's only a 19 mm diameter shaft if I remember correctly. The support bearings tend to creep around inside the torq tube if really driven hard regularly. Automatic, have you checked the driveshaft creep forward to the crank thrust bearing? I'd check that every year just to be safe.