Triumph Repair: vibration felt through seat, shaft vibration, air fuel mixture

Question
1976 triumph spitfire,

I feel a heavy vibration only when accelerating at high rpm.  Just started recently.  The only thing I changed recently was air fuel mixture and idle speed.  Doesn't matter if in overdrive or not.  If at high rpm and not accelerating there is no vibration.

Answer
Hi Curtis,

The first thing I would look at is a "U" joint as that is a normal indication of a "U" joint going bad. Not just on the drive shaft but the two on the rear axle. I have been able to separate the axle and the drive shaft by the frequency of the vibration because the drive shaft is spinning faster then the axles. So the drive shaft vibration is a finer vibration.

Some are hard to spot, but they usually have rusty grease on the bad ones but not always.

Howard