TCMgo

I searched this forum before posting this thread, as I could not find much on my issue. Perhaps, I did not use the correct search language. I drive a stock 1997 XJ sport. This latest noise just started in the last few days. Both when de-accelerating or when applying the brakes I can hear and feel a loud deep vibration. It goes away the second the gas is applied. 1,000 miles ago I had the differential rebuilt. 200 miles ago I had the upper and lower ball joints replaced and the front end aligned. About 70,000 miles ago I had all of the u-joints replaced. Could it be a bad rebuild on the differential, a problem with the alignment, a bad u-joint? I am sure there could be a whole litany of causes. Have any of you had this problem? Any suggestions? Thank you for your time.

TrailerTrash

My first guess would be the u joints. When you are on the gas there is "tension" or load so to speak on the driveshaft. When you let off the gas the driveline pinion angle will change slightly. When you get on the brakes it can change a little bit more. Plus if leaf springs and bushings are bad the axle can "wrap" so to speak. All of this pretty much happens all the time but if the u joints are bad it can cause noises and vibrations.

You can check the u joints by firmly grabbing the driveshaft on their side of a u joint and twisting them back and forth in opposite directions feeling and watching for play. This isn't a definitive test because they can be bad and not have any play or noises.

Another thing to check is the motor mounts and trans mount. They could be bad or even collapsed causing vibrations when off the gas due to the same effect I mentioned above.

TCMgo

Thank you for the quick reply. I replaced both the transmission and motor mounts about a year ago. I will definitely look into the u-joints. For about a year before I had the differential rebuilt, it was making a strange grinding noising when taking off from a stop, especially while turning. The noise would go away after about 5 seconds of acceleration. It turned out to be a worn carrier. I am wondering if it caused a premature failure of the u-joints (which were replaced about 70,000 miles ago), perhaps the rear one. I will see. Thanks again.

Dave51

Clean and lube the slip yoke. Check all 4 wheel bearings.

TCMgo

Thanks for the reply. I will also look into the slip yoke and bearings.

cruiser54

Look here. Bad trans mount and/or worn motor mounts can cause issues.