As the title suggests.

A Bad Vibration in your arse lol!!

Vibration felt through the center of the car (seat, floorpan..etc) , typically at 50-60mph (ish), but can appear lightly at other speeds,and severely under hard acceleration.

 

Can also be caused by worn/notchy Drive-shaft joints and by a sagging rear gearbox mount, which alters the angle of the prop-shaft and causes increased wear on the bearing.

Edited February 11, 201213 yr by Yowser

What about slow accelerating in 1st, coming off the accelerator pedal and feeling a "back and forth" kind of judder like there's excessive play in something... What might that be?

If the rubber support thr bearing sits in perishes it can knock under initial acceleration and deceleration .