terrapin

74 Delta 88 w/ 455 and 12 inch 9 3/8 rear w/ factory limited slip

-Purchased in July w/ 34k miles, now has 35k on it.
-Noticed slight rear end whine under light throttle and coast that seemed to be getting a bit worse.
-Finally changed the rear axle fluid today and it was black sludge and I imagine original.
-Diff gears looked perfect w/ no signs of wear
-Cleaned all the crap out of the housing etc and filled w/ new 80W90 fluid and friction modifier
-The noise is still there

It sounds like ring and pinion noise which I have heard before in older pickups I used to drive for work

Could this possibly be coming from the TH400? My next step is to replace that fluid and filter, but it does not seem burnt when I check with the dipstick. I imagine that is original as well

Thanks for any guidance,
Ed

Olds_71_442

I used to have a 79 Delta 88 and the rear end used to whine. It was one of the outer bearings on the rear end gear housing.

64Rocket

Pull the axle's and check the axle bearings.

Gene

terrapin

Thanks guys. I always thought that bad bearings always made noise regardless of throttle input etc. When I coast there is absolutely no noise.

oldcutlass

It could be something as simple as a Ujoint. I have always found that a lift works well in tracing down these type of noises because you can get underneath and rev the car in gear and 9 out of 10 times isolate it or eliminate some of the obvious suspects.

terrapin

I wish I had access to a lift, but I don't. I have good local mechanic that I trust so I guess I'll take it down there.

The u-joints seem tight, but I suppose there could be some issue with the double cardan CV in the back

oldcutlass

You can always throw it up on jackstands and be very carefull.