Vibration in Clutch Pedal
> My 86.5 5 speed has a vibration over 3000 rpm and can be felt on the clutch
> pedal and gear lever. I was told that the clutch fork bush needs replacing
> and the transmittion needs to be removed to access the bush.
> My question is do you need to drop the transmittion at access the bush and
> will this stop the vibration.
That's not even close to the right cause for those symptoms! When you let out the clutch the whole pressure plate assembly turns with the crankshaft so the central shaft assembly and throw out bearing as well as the guide tube are taken out of play. Also, 3000 RPM vibrations are famous in 928's. That long drive shaft running at engine revs was a dynamic nightmare for the development engineers. They made it real good by carefully positioning the bearings in the torque tube to eliminate natural frequencies. The tranny and motor mount durometers and positions are also a factor so if they aren't up to factory specs then the natural frequencies show back up. Annoying but true.
Moral: your symptoms point most likely to bad motor mounts, or bad torque tube bearings.
Definitely don't need to remove the tranny.
I have this very vibration only it starts at 4,000 rpm and goes all the way to 6,000. I have determined these things: If I run it up to 5,000 in first, push in the clutch and let the engine idle down the vibration is still there because the speed of the car has the drive shaft still spinning at 5,000 rpm. Push the shifter into neutral and the vibration goes away. All this tells me that the vibration is between the input shaft of the transmission and the pilot bushing in the flywheel. The twist to all of this is that depending how hard I take a corner I can actually make the vibration go away completely. All of THIS tells me two things. I have bad motor mounts and I better remove the entire drive line and look for possible cracks etc. because my drive line is not as rigid as I think it would normally be.
1978 928 5-speed
928 Tips Home Greg's Home