rear end sound/vibration
 

I just recently swapped in a five lug LSD rear end from an 87 gxl into my 86 base model FC. I put brand new rotors and calipers on it. I get a weird vibration/sound from about 5mph and up. It increases with speed and decreases while slowing down. it kinda sounds like a rhythmic "whoomp whoomp whoomp"...its still there with the clutch depressed. only time it goes away is during right turns. Ive tried doing some searches and couldn't come up with much. the only thing I have noticed while trying to troubleshoot is that the passenger rear caliper seems to stick a little more than the drivers side. Ive visually watched the everything moving while on jackstands and in gear, didnt see anything out of whack. everything was torqued properly. rear wheels had no play while I had it jacked to see if possible bad wheel bearing. no difference if I have my rear sway bar hooked up or not. any ideas on what my problem could be? I really hope its not the diff, and I dont think it is since the problem disappears during right hand turns.

does the driveshaft need to be installed in one way? as in is it balanced and I have it installed in the wrong orientation? would spinning it 90* or 180* or 270* and reinstalling it do anything?

I have read that some driveshafts are particular with the orientation. But that would likely show up as a vibration and not a noise. Did the new diff have solid mounts?

no, it had stock mounts. it does have a vibration, but also the sound that goes with it. there is no metal grinding sound, just a kind of out of balance sound that is very rhythmic. tomorrow I will try re-orienting the driveshaft and see if that helps. its just that when i take right hand turns it goes away which makes me think it may not be driveshaft related. also, there is no increase in sound/vibration while making left hand turns.

i think ill have one of my friends ride in back to see if we can figure if the sound is coming from the left, right or center of the car. A caliper that bites a little harder shouldn't be a problem like this should it? the car doesn't pull in any direction and has no extra drag when coasting like one with a blown/stuck piston. I also completely flushed the brake lines and have all new fluid, fully bled properly. New gear oil w/ LSD additive in the diff as well. before installing the rear end I went through to make sure there was no grinding/binding/rubbing anywhere from where the driveshaft bolts up to the hubs. It all felt great. and there were no problems with my old 4 lug/ open diff I pulled from the car beforehand.

your driveshaft orientation does not matter. I just went though a shit ton of work figuring out my rear end issue. search threads ive started. Should say something about driveline.

Do you have any clunks at all, or just wonky vibration?

sounds like a wheel bearing. could also be a backing plate rubbing on the rotor. rusted rotors can do it also.

but if you make right turns its most likely the left wheel bearing.

no clunks, just the wonky vibration with a low pitched rhythmic sound that accompanies it. More sound than vibration until around 35mph...and I just dont feel comfortable going faster than that. All backing plate/dust shields are not hitting anything. I guess I'll just replace wheel bearings, then axles, then bushings. try and isolate the problem whilst replacing my rear end components. hopefully its not the diff.

@Riggs - Ill read through all your posts and see if they help, thanks

@J5sense - if the sound doesn't happen on right turns and it is a wheel bearing issue, wouldn't that rule out the left side since its rotating more than the inside (right) wheel? which in theory should be putting more stress onto the outside wheel assembly.

could this be a bad differential issue at all? it is a clutch pack style lsd, I personally dont know much about them at all. I still have my open diff if it turns out to be no good.

im just annoyed at driving my 81 subaru w/ a whopping 60hp=no fun.I miss rockin the rx..but i do save $100 a week in gas

duh. typo!

your right

when you turn right or the best way to duplicate it is a long right on-ramp. the weight transfers to the right allowing that bearing to be loaded. it then can make all kinds of noises. try that bearing first and go from there. thats what i would do based on the info given.

ill give it a shot, i got a nice business park nearby i can try it in. thanks