Drivetrain Vibrations please help

[stevehank]

93 a/t gsx with mods, heres the problem:


Under light throttle, crusing at 25mph, under my feet while driving I can feel vibrations and the wheel shake. It doesnt shake like something is wrong in the steering.

When I give it more gas it smoothens out. Any faster than 25-30mph there is no vibration.

I really dont think its steering, I can take really hard turns and turn all day, and its fine. I think its something with the transmission/drivetrain. The transmission shifts perfect. I can race the car and it runs perfect. The vibrations are only felt when crusing at 25-30mph WITH MY FOOT ON THE THROTTLE, if I take my foot off, it stops. Any Ideas? Thanks alot.

 

[TalonJohn94]

Its probably the famous "rear-differential shim" that goes often.

Or U-Joints or Carrier bearings.

Also, vibrations are always felt at lower frequencies.

I can even feel increased vibration between shifts.

I have a lot of vibration but its because I replaced the fatigued-rubber-dampening-insulators that hold the D-shaft carrier bearing up with washers.
Does anyone know if that was a mistake?