I installed a new rear end last week, now at 70+mph the car has a really bad vibration of the whole car. I am wondering if it could be the alignment, or possibly the rear sway bar bushings(they looked like they needed to be replaced soon) so I am about to drop it off at the local alignment shop today. any suggestions other than that? maybe wheels need balanced? (they were just balanced last year fall.

It doesn't do it at all when going under 70mph

 

First things first:

Is the vibe at wheel speed (wubbawubbawubbawubba) or drive shaft speed (mmmmmmmm)?

No it is not sway bar bushings.

Changing the rear end probably didn't affect wheel balance, but what do I know anyway.

Same for alignment.

If it's at wheel speed, suspect a bent axle.

 

I put it in drive on the lift after the installation and put it in drive so can't bent axle. In fact the rear I just swapped out had a bent axle that was extremely bad and it gave me no vibrations.
I'm wondering if its u joints or driveshaft.

 

Im having the same EXACT problem :/

 

was the rear end you installed brand new? or used from another car? did you use the same brake drums or new ones? they can be out of balance.did you swap the rear wheels from one side to the other? is it the same exact model of rear end? if it's different, maybe you changed the driveshaft angle slightly which now makes it vibrate....lots and lots of possibilities....

 

My rear end was swapped from an 87 with discs.

 

It's hard to carry on 2 converstaions at the same time, but since the interruption is pretty similar to the 1st one, I'll try...

Is it at wheel speed (wubbawubbawubbawubba) or drive shaft speed (mmmmmmmm)?


No further troubleshooting can occur until this one extremely simple question is ansswered.

 

while drive shaft speed and wheel speed are directly proportional, that is actually one of the best ways I have herd the difference between them described

so OP, which is it?

 

i apologize for interrupting. Mine is seems like it is at wheel speed.

 

^ put the rear end on jack stands, chock the front wheels VERY well, and have some you trust run the car up to ~50-70mph (wheels a few inches off the ground). Look too see it the wheels/tires are bent, out or round, (wobbling/bouncing). IF they are then it's a wheel/tire/axle problem. The take the wheels off, and do the same thing with the axle flange ("hubs"). If neither the wheels nor axles seem to be an issue, it's probably a driveshaft issue

let us know what to find!

OP you can try this same procedure

 

steel driveshaft + deep gear change = vibration at ~70

 

i did put mine on my shops lift and no bent axle, i have 3.08 10 bolt. I went from 9 bolt disk to drums and did use the same old drums. My driveshaft still has the weight on it so it should be that. I shook my wheels with all my weight and one seemed to clunk more than the other.

Its not a wubbawubba or mmmmmmm but more like it shakes the dash pad and us inside the car at the higher speeds.

 

mine has the wubba and an occasional grawrgrawr coming from what seems like the left wheel......

 

Try flipping the driveshaft 180 degrees. My 88 did the same thing. Flipped the driveshaft, no vibes.

 

just wondering, when i did my swap i took the springs off the donor car. they were a bit smaller and my car sits lower. could that have anything to do with it?

 

i am very interested in this too. SAME ISSUE. Swapped out rear and now has vibration. Mine is anything at 45 or above, its not noisy - it shakes the dashpad and inside the car. Faster you go, the worse it gets. Changed out the driveshaft and tires, and still have vibration. We took it from a 87 9 bolt posi to an 89 rear posi - disc brakes and all. Would a bent axel get worse with speed?

 

a bent axle would get worse with speed. you can check your axles by running it on jackstands with the wheels off. put a couple of lug nut on to keep the rotors from wobbling....then just run it slowly..you should be able to see if the axles are bent....it may take a carefully placed straight edge to see the wobble- even a very tiny amount can make a vibration..that's what i would try next anyway...i had this issue on my old 62 cadillac....

 

i took the tires off and the rear end is wobbling out of control. wtf

 

Me and IROCINCO have the exact same swap and problems.. I'm going with bent axles

 

do you have at least two lug nuts on each hub? let it run very slowly and visually check for bent axles....

 

if you don't have it at lower speeds, would you actually be able to see the bent axle with it jacked up off the floor? or would you need to take it to a dynamo? I guess this sounds silly, but i've never had a car with a bent axle before, with the tires off, what am i looking at/for? Would you see the vibration? Or would it just look....off?

 

you will only be able to see it when it's spinning very slowly....if it's turning over fast it will just look like it's vibrating.....a bent axle doesn't mean bent by like 1/2inch.....it's like a matter of millimeters.....

 

...outcome?..

 

Instead of jacking the back up and running at speed, which is very dangerous, just have someone follow you down the road. A bent wheel can be very easy to spot.

 

it was the drums on the rear end I bought. Someone painted them leaning up against a wall. The paint ran down and put them off balance. I built the rear end to find out it was the drums. LOL oh well.

 

I love the whole wubbbawubba sound effect i was LMAO when i read this lol

 

Has anybody thought about checking the pinion angle? I thought I read in there somewhere that you changed the rear springs as well. Might be worth a shot to double check your pinion angle. Only takes a few minutes and is completely free if you have a magnetic angle finder.