Swapped axles got a bad sound

[jessica2112]

Hey, I put in a new rearend with 3:42's. We did it at a shop. Had two good mechanics helping me. Did everything right, everything is tightened as it should be and I have a really bad thump from the right side. Going over bumps. Alsmost sounds like an exaust rattle, but we didnt even mess with it. Anyone have this problem? It was a straight swap out, 99 rear with 3:08's to a 00' LSD w/ 3:42's. Axle has 26,000 miles on it. Sounds like someone is hitting the right rear underside with a mallet.
We put it back on the lift and it is all tight. We used a prybar and moved stuff around, up and down and shook the exaust. Nothing. The only noise I could get is when it was on the lift and the weight was off the springs. I could make the passenger spring clink on the round base that it sits on. We tightened everything up when it was in the air.

[Arctc Wolf]

if the lca's are tightened when the rear has no weight on it, you will get a bang from the bolts not being loaded when they're tightened.

[jessica2112]

Does it do that all the time? I mean when I drive it its every other bump. It's like having the hatch popped and driving around.

[carmelcarswholesale]

just a long shot, but did you check to see that the rubber spring isolator is in place between the top of the spring and the unibody?

[jessica2112]

Yes, they are both there. I don't get it. Its pretty bad. Driving me crazy. Sounds like the hatch is open when your driving the car. Or the door is not closed. Rattles alot.

[carmelcarswholesale]

Hah...I just remembered something else....did you add the tube of GM limited slip additive to the rear end oil when you buttoned it up? This special additive is required in all GM limited slip rears to keep the LSD locking and unlocking noise from bothering the driver!!..otherwise you get a clunking that is loud and gets louder the more you drive as the gear oil heats up...if you didn't add this, just get a tube at your GM dealer and put it in through the side plug on the rear end case...bet this is it if everything else if tight and in place...good luck..Richard ...ps (will be digging in the warehouse next weekend for your AC compressor)..for gear oil we use Redline special rear end oil

[carmelcarswholesale]

And I'm assuming you did change the gear oil and filled it to the proper level?

[blackFbird_98]

i would bet that it is the lca's werent tightened with a load on the rear axle so they are making a noise anytime the axle is unlevel with the car

[grayman]

Did you guys put a load on the rear suspension as mentioned in the posts above? If the car was suspended by the frame when everyting was tightened it should also have had a jack under the axle...pushing it up to simulate the weight of the car on the suspension.

[camarocrzy]

I also have the same problem, whenever i hit a bump i hear this thump from the rear. It sounds like the shocks bottoming out but iput knew ones on and it still does it. But that isnt the only problem ive been having since doing it. I think i tightened everything up when i had the frame jacked up and the rear just hanging with no weight on it. Ill try and retighten everything like mentioned above. Its just so annoying!!!

[jessica2112]

Yah, Thats the problem I have. camarocrazy has the same thing. We had the axle on a stand when we tightened it. I did have the R R break messed up. The outer pad was seated wrong. Got that fixed this morning, but the rear end still rattles. I even checked the spare tire. It does it on every bump. I am getting really pizzed.

[grayman]

something to try is to take the car into a shop that has a roll on lift. (all four tires on the lift) Get the car up in the air and loosen all the suspension components and then lower the car down a bounce it up and down a few times. Lift the car back in the air and torque everything down to spec.

while you are under there also check that the exhaust system was re hung correctly.

[carmelcarswholesale]

And here's one more idea that might cause a clunking sound...check your torque arm forward bushing that mounts to the transmission...if it has worked loose it won't be obvious until you drive it and then you'll hear clunking as you go over bumps or brake...since the torque arm came off for the install it's worth checking...good luck...rp-

[camarocrzy]

I finally got my thunmping noise fixed!!! I took my car to Monroe to put on my replacement muffler and asked the technician what he thought that noise was, he put the car up on the lift, figured it out in a second and fixed it no charge. He repositioned my springs and tightened my shocks with the impact wrench and voila, no more noises. Finally my car is back to normal. I was so frustrated.

[jessica2112]

Really? Wow you have great luck, no charge. Did you have a chance to watch? I was thinking of trying to reposition my springs, but don't know the correct way. How they should look. Glad you got yours figured out, thanks for sharing the info! Thanks to the rest of you all too. Saturday I will have a chance to take it back to the shop and spend some time on it.