Help diagnosing rear end noise

Maxpowers · May 7, 2012

Started getting a thumping from the rear end. It becomes very noticeable at highway speeds (45+). It's hard to tell before that due to the loud exhaust. Sounds like the noise gets louder under load. It doesn't seem to change with turning.

I found that one rear tire had a flat spot on it. I put new tires on, obviously a good balance.
Checked the U-Joints. They both appear ok. No slop and no rust.

I pulled the diff cover tonight and checked the gears. They all appeared ok. Filled it back up with fresh fluid and friction modifier.

Any ideas?

johnnyt03gt · May 9, 2012

going just by what ur saying. and the flat spots on the tire you mentioned,

i would suspect a broken rear shock. OR possibly a LCA bushing,

Maxpowers · May 9, 2012

My guess was the flat spot was from parking it for the winter without being able to lift it or move it from time to time. This issue has been happening since last summer.

Shocks are brand new. LCA's are stock. Would that create a thumping sound?

johnnyt03gt · May 9, 2012

best thing to do is. jack up the rear and set her on stands. get under the rear end have someone push down on the rear. while ur investigating looking for the problem,

could be a lots of things. shouldn't any big issue just gotta get underneath and look.

again, i must emphasise safety first. i almost died last year the floor jack slipped off the K-member. while i was underneath the car, luckily i had placed jackstands along the frame.

Maxpowers · May 13, 2012

johnnyt03gt said:
best thing to do is. jack up the rear and set her on stands. get under the rear end have someone push down on the rear. while ur investigating looking for the problem,

could be a lots of things. shouldn't any big issue just gotta get underneath and look.

again, i must emphasise safety first. i almost died last year the floor jack slipped off the K-member. while i was underneath the car, luckily i had placed jackstands along the frame.

I guess I wasn't specific enough. This isn't a suspension issue. It's a repetitive thump that seems to speed up and slow down with the vehicle speed.

demented22 · May 13, 2012

Possible bearing in the rear end? I never really had many problems with rear axles that I did not cause. (burnouts in my truck with 35's split diff in half) I would get it up in the air and investigate asap!

Maxpowers · May 14, 2012

demented22 said:
Possible bearing in the rear end? I never really had many problems with rear axles that I did not cause. (burnouts in my truck with 35's split diff in half) I would get it up in the air and investigate asap!

That's most likely my next guess. Either that or a tooth being chipped off the 28 spline rear axle.

Maxpowers · Jun 5, 2012

Seems like the issue has been fixed by changing the fluid. Makes me think the previous owner didn't use any friction modifyer. Not sure what else would make those noises.

trinity_gt · Jun 5, 2012

The friction modifier would only affect the operation of the clutches in the limited slip. If you were experiencing a chattering while going around corners the friction modifier generally addresses that.

How much fluid did you drain (i.e. was the fluid level low to begin with?)

Maxpowers · Jun 6, 2012

trinity_gt said:
The friction modifier would only affect the operation of the clutches in the limited slip. If you were experiencing a chattering while going around corners the friction modifier generally addresses that.

How much fluid did you drain (i.e. was the fluid level low to begin with?)

It was full. That was the first thing I checked when attempting to diagnose the issue.

I know issues don't fix themselves, so either the fluid changed fixed it or the problem is dormant.

What would the wrong weight oil do?

Help diagnosing rear end noise

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