Driveshaft bouncing at the rear diff.
Hi all, this is my first post here. I have been reading for a while and will try not to ask what has already been asked numerous times.
My issue is mainly with a vibration which occurs predominantly on acceleration, at speeds of 30-40mph or so. If I let off the gas it seems to go away. At higher and lower speeds it seems to go away as well. It vibrates the steering wheel, as well as what feels like the body/seats etc.
I already removed the front driveshaft, there was no change.
I jacked up and inspected the front end as best I could, wheel bearings, hubs seemed ok.
I jacked up the rear of the vehicle, and placed jack stands under the rear axle and had someone else put the vehicle in gear and get the speedo up to 30mph or so. I could hear some grinding noises coming from the driveshaft/rear diff area. Looking at the driveshaft where it joins the differential, it rotated normally at first, but as the speed increased, it took on more of a football shaped rotation, and I could see it bouncing around.
I turned the vehicle off, and grabbed the driveshaft at the diff, and pushed side to side and up and down. Up and down there was some movement, but none side to side.
Oddly, when I lowered the vehicle and tried again, there wasn't really any movement.
Am I looking at a bad pinion bearing? Bad U-joint? Driveshaft?
If it doesnt list elsewhere, this is a 1997 Grand Cherokee, with a 242 Transfer case, 4.0 engine.