Ok, Moderator, I'm not sure if this is the right board. But I've tried the LS1 board, and didn't get much help there. So please bear with me. Thank you.


I have a sound from the rear of my car. Specifically in the rear axle area. It is NOT a clicking or ticking sound (indicating a chipped tooth of the ring gear). It is NOT a whining/howling sound. (indicating a bad bearing). I have had both U-joints replaced and packed with plenty of grease, replaced the pinion seal, changed the fluid, put a limited slip additive in, pulled off the diff. cover and closely inspected the gears. Everything looked perfect.

The sound is very difficult to describe. It is like a low low growl, but at the same time sounds like a low pitched grinding. The kind of grinding that you can feel in the seat of your car. It also is like a tearing sound. Kind of like holding 4 pairs of jeans on top of each other and tearing them apart all at once.

This sound occurs under hard acceleration from a stop, but not hard enough to spin the tires. Also on a 3rd to 1st downshift and the 4th to 2nd downshift on the freeway an at speed. Does this make any sense? Can anyone help me track this down? Last thing I want is my rear end to blow out on the track or worse, on the freeway.

 

Thoughts:

It's driveline torque sensitive: max accel and full throttle downshift. My guess is the driveshaft is contacting something under those conditions. Floorpan or brace thereon is the usual suspect. You feel driveshaft rub, and tearing jeans is very descriptive. Anything you do to the floorpan to cause noise is transmitted throughout the car.

It's easy to check: look for circular rub marks on the driveshaft and the underbody. Cure. Stop carrying around those 2 fat Roadies for traction.

Reshaping the critical area of the underbody with a standard BFH usually works.

If that's not it....maybe tire rub? Are the rear meats 1) oversize or 2) on different offset wheels from stock?

If it ain't one/both of those....well, you could sell the car. I'll keep thinking on it.

My $.02

 

checked the driveshaft at the shop, no marks on it or the floorboards. The tires are stock SS size. I'm not sellin it, especially since everything checks out ok.

Thanks

 

Hmmmm........

You added the SS wheels? Are they GM or aftermarket? Look carefully in the wheelwells for rub marks where the edges of the tread might be hitting something. There appears to be ample clearance on the inside (on a 2000 SS anyway), but it's tight on the outside if the car is really low.

Still thinking.

 

The wheels are GM, not aftermarket. My car isn't lowered. No wheel rub yet. Thanks for the help. Keep thinking.......thank you

 

what about your rear suspension? i've never heard of a sound coming from bushings but maybe try to get someone to bounce the back end and listen for suspension components rubbing maybe ?????

 

that was the first thing I checked. Since I put new shocks on, not a single noise out of them or the bushings. Thank you though.

Anyone else?

 

I talked with a few people and had them listen to it. The ideas i got were:
cracked flywheel (unlikely)
dying torque convertor (possibly)
bad posi unit
or
trailing arms or LCA i think.



Also, my torque arm on a 4-1 downshift will give my center console a WICKED SHIMMY (big bang/jolt). Any thoughts?

 

Most likely a broken trans mount, i had that happen quite a few times before i went to a polly unit.

 

at one point in time the tranny mount was broken, but I had it fixed. When I took it to the shop to figure this out, they checked that too, and it is fine. I think it is a stock mount though, not polly.

 

I finally found out what was causing all of this racket!

Motor mounts! Two of them were broken in 2. They were all replaced, and the trans mount was broken too, replaced with poly mount.

So i guess this is what happened. Stressed motor mounts finally gave way allowing engine flex, putting more strain on the tranny, breaking the mount causing varying angles on the u-joints, transferring to the rear diff, through the axles, to the wheels to make that horrible sound.

Well, its all fixed now. So the lesson is, if you motor mounts look a little stressed, replace them.