Whirling/Thumping sound rear end
 

Hello all:

My girlfriend has a 98 GMC Jimmy 2wd. It is in good shape but has 186,000 miles. There is a whirling-thumbing sound coming from the rear end only when the car moves. It makes the noise even if you back off the gas. This started 3 weeks ago. Also, we now notice a delayed shift from 1st to 2nd. Not too dramatic but there. The tranny fluid is bright pink and not burnt. It appeared to be at correct level when I checked it a month ago.

My questions are:

What could be causing this noise around the rear end?

Is the rear end causing the 1st to 2nd abrupt shift or is this unrelated?

Appreciate the help!

Thanks in advance!
Ryan

1st I'd check u-joints for that thumping sound, look for play between the drive shaft & the yoke. Also you may want to pull the rear diff cover & look for debris in the oil. I'm not too sure about bearings in the rear axles but it's tough to think of them thumping. I had a diff that fragmented part of gear & it would lock up tighter than a drum at any speed it liked lol. THAT was fun when it happened doing 50mph!
Brake stands as a kid with a govener driven posi in a 1980 sierra grande 4x4. ooopth lol

I doubt they have a connection. Sadly when my 4L60E had a delayed shift from 1st - 2nd & going into reverse when cold in the winter, Lucas Trans Treatment helped a bit but I did have to get it rebuilt & upgraded at the same time, just 'cause. Lucas Mucas may help the shift issue but it's only a bandage of sorts.

^^^, +1