Hello All, just some help on a problem im having. Im getting a bad vibration in 5th and 6th gear at highway speed. Car has a new poly tranny mount, what else could be causing the problem. Thanks

 

You posted in the meet and great area. You should post in the 4th gen tech section.

You have checker you U-joints. Is the vibration only under power or does it do it while you are costing also?

 

moved your thread to the 4th ten general section. poly mount transfers vibration better. try a stock one. also your bushings in the back control arms may be worn and letting the rear end move to much.

 

Gorn,


It only vibrates under power. and it is extremely bad you feel in the shifter. the lower trailing arms have been replaced with Spohn performance trailing arms along with pan hard bar.

 

Bad main shaft or input shaft of the tranny. U Joints. Tail shaft bearing. Pilot bushing/bearing....those are my guesses.

 

yep, check u joints for damage or wear. torque bar mount may be letting the torque bar move up as you excel. did you have a look at it when you where changing the trans mount. be a good idea to check you pinion/driveshaft angle. motor mount may also be worn allowing the engine to lift on excel changing your driveline angles.

 

A poly trans mount won't create bad vibrations, but it will transmit bad vibrations that are present that were absorbed (masked) by the rubber mount, to make them more noticeable. I'd leave the poly trans mount in place, since that's not the cause of your vibes, it's the effect. If the vibration is speed related, and not rpm related, you can pretty much rule out clutch related (btw, the pilot bearing doesn't come into play when the clutch is engaged). You need to get the back end in the air and do some exploratory turning and twirling of everything. Bad u-joints and wheel bearings can show up at different speeds, can also be bearings inside the trans related to 5th and 6th gear.

 

Isnt the main shaft always spinning when the clutch is engaged since its splined and being turned by the disc/PSI plate?

 

When the clutch is engaged (while driving), the crankshaft, pilot bearing, flywheel, clutch disc, pressure plate, and input shaft are all spinning as one locked unit.
The input shaft free wheels inside the pilot bearing only when the clutch is disengaged (clutch pedal depressed).

 

Ok, cool....thanks for clarifying that for me!