The rear of the car shakes

[SocketB]

The rear wheels turn when both rear wheels are off the ground while the car is in park, the car also shakes in the rear when the speed of 30 miles an hour and up in the is reach, is this because of a bad pinion bearing?

This is a 1993 Cadillac Fleetwood Brougham

[Blue Bowtie]

If the car is raised and the wheels/driveline is turning, the rear axle is hanging free and not in its normal position. This can substantially alter the pinion / driveshaft angle and potentially cause vibration.

[maxwedge]

The rear wheels both turn in park? Are you sure, this can only happen turning them individually one at a time, non posi rear. A bad pinion bearing would usually be noisey. Your info doesn't add up.

[Blue Bowtie]

MW - AFAIK, the '93-96 models used a gov-lock which will not engage at low speeds, and those with traction assist had an open diffy (out of necessity) to work with the automatically-applied brakes on the slipping wheel. I'd worked on a Roadmaster of that vintage with that option and wondered why there was no locker.

You're right, though. Some of this doesn't quite add up.

[maxwedge]

Yeh, about the Eaton locking diff, needs a 100 rpm difference in rear wheel speed to lock up the dif, had it on my S10 years ago.

[SocketB]

Originally Posted by Blue Bowtie

If the car is raised and the wheels/driveline is turning, the rear axle is hanging free and not in its normal position. This can substantially alter the pinion / driveshaft angle and potentially cause vibration.

The driveline did not turn, the wheels turn while the car is in park meaning when i spin the wheels using my hand, this shouldn't happen and i also put the car in Neutral to see if the driveline turns the driveline did not turn.

[Blue Bowtie]

The photos you posted show an open differential (non-locker/non-posi).




When in park (driveshaft not moving) the rear wheels/axles CAN turn freely due to the differential gearing. They will turn in opposite directions, however.

[SocketB]

Yes they did turn in the opposite direction, and my bearings including the ones left and right on the differential are good and the pinion bearing is good so the rumbling noise is coming from somewhere else i really would like to know where.