Hi everyone,

I have been having a problem since I first bought my car a couple months ago. I will try to make this as clear and concise as possible.

1997 Mustang GT Automatic; 119,000 miles. CAI, SCT Tune, Magnaflow Catbacks

Things done since purchase are plugs, wires, coils; PCV; tranny flush; rear axle bearings, aluminum drive shaft, differential rebuild with FRPP 4.10 gears and bearings; fuel filter change; oil change; front and rear shocks, struts, front swaybar bushings, endlink bushings.

What I have is a pulsating/intermittent vibration that gets faster and louder/more noticeable at higher speeds. It is related to speed if I had to take a guess. It continues if I let off the gas while moving but will stop if I am moving at highway speeds and put the car in neutral. The local performance shop diagnosed it as the rear axle bearings. Those were replaced, then it was diagnosed as the ring and pinion. The diff was rebuilt with a trac-lok kit and motive bearing kit as well as FRPP gears by a reputable shop. I elected to replace the driveshaft which was also done professionally with the yoke changed to match the spline on the auto tranny.

The tech called it a "growl". None of the repairs I have done have made any difference. The diff fluids have been drained twice now. The only thing I can think it might be is that the rear upper control arms need replaced which is causing the pinion angle to be off.

Sorry for the long read. Thanks for any help.

 

Have your tires rebalanced. Might not help since you say it goes away when you take the load off but it can't hurt. I was thinking rear diff or u-joint until I read that you had all that replaced.

 

Driveshaft balance must be better than perfect for a highway driven 4.10 geared car.