Is my rear-end F****D?

This just started today when I was out driving around. Loud banging from the rear of the vehicle kind of randomly, sometimes on the right side and sometimes on the left. It will usually do it after i've made a turn, straighten out, and hit the gas but not always. Or after i've stopped for longer than a few seconds, and start to go again (doesn't seem to do it if I just stop and go). It's not a continuous bang, just one loud bang, sometimes two. It's as if something is getting caught and releasing harshly.

Also when i'm turning lately, I get a nasty shudder throughout the car seemingly coming from the rear. As if the rear tires won't/don't want to spin at different speeds. And it seems to be getting worse the more I drive.

The car sat for almost a year up until about a month ago when I brought it back out for the winter months. I don't recall it having that shudder on turns last year.

The rear differential fluid was changed probably about 5k miles ago, and I looked under there briefly tonight and it doesn't look like it could have leaked out.

Am I looking at a whole new rear end here? Could it be something else?

The car is an electrical nightmare (move the muffler and all the lights shut off/on, among others), but it has always been a reliable runner. Now I don't think I should continue trying to drive it. I have a 60 mile trip I have to take Monday morning in a snow storm, don't really want to get stuck. At the same time, however, I don't want to drive my summer car in the snow (even if it is AWD).

Thanks guys.

Oh yeah, might as well add this: Whenever I used to do a brake stand or a burnout, it would leave two nice and even tire marks. Well I did one burn out a couple weeks back and it left a nice one wheel peel mark, that had me puzzled. Figure it might have something to do with this?

Only thing I could suggest is to jack it up, and pop the rear diff. cover off and have a looksee. See if you find any broken gears inside and check the cover magnet for an abundance of "more than normal" metal shavings.

Roger that. Just need somewhere without snow to do it. :(

Well, you HAD a limited slip differential. What has happened is the limited slip govenor has shelled out and probably damaged the ring gear as well. I know because I went through this same thing on my 85 when it had 35k miles on it. At the very LEAST you'll need a new differential carrier, pinion bearings and a complete flush of the rearend, including axle tubes. STOP driving it or the damage is only going to get worse.
The the pre 90 third gens came with very weak Saganaw limited slip units that couldn't even handle the power that the little 190 HP 305's threw at it. GM's fix for this was to replace them (when they blew up under warrenty) with the MUCH stronger Auburn carriers.
If you want one of these carriers you can contact Summit and see if they still have them (they used to).
I was fortunate enough to have bought an extended warrenty when I bought my 85 IROC and it paid for itself a couple times over when all was said and done. The work and parts were $1800 back in 88, I shudder to think of what the labor charges would be now.

Well, you HAD a limited slip differential. What has happened is the limited slip govenor has shelled out and probably damaged the ring gear as well. I know because I went through this same thing on my 85 when it had 35k miles on it. At the very LEAST you'll need a new differential carrier, pinion bearings and a complete flush of the rearend, including axle tubes. STOP driving it or the damage is only going to get worse.
The the pre 90 third gens came with very weak Saganaw limited slip units that couldn't even handle the power that the little 190 HP 305's threw at it. GM's fix for this was to replace them (when they blew up under warrenty) with the MUCH stronger Auburn carriers.
If you want one of these carriers you can contact Summit and see if they still have them (they used to).
I was fortunate enough to have bought an extended warrenty when I bought my 85 IROC and it paid for itself a couple times over when all was said and done. The work and parts were $1800 back in 88, I shudder to think of what the labor charges would be now.


Ugh, that's not good news. If that's the problem, it sounds like it's gonna get a junkyard rear-end or a rebuild w/o limited slip (if possible). I read up some on the posi rear end rebuild and the one site said it would be a good $2500, and i'd be better off getting a 4th gen rear end. I posted this on 3rdgen.org and a couple of those guys were saying it sounds like the tranny mount broke? Which is very possible since I hit a massive chunk of ice that scraped the whole underside pretty hard. But at the same time i've been doing an inordinate amount of burnouts and donuts lately, and it feels more like a differential problem to me. It's off the road for now, driving around the VR4 on summer tires in the snow. I guess i'll update when I get a chance to look at it.

and i'd be better off getting a 4th gen rear end.

That was my first thought. :grinyes:

HAve you visually inspected it yet? Anti-roll bars and torque arms make some noises in the banging catagory when they go bye-bye.

I posted this on 3rdgen.org and a couple of those guys were saying it sounds like the tranny mount broke?
Also when i'm turning lately, I get a nasty shudder throughout the car seemingly coming from the rear. As if the rear tires won't/don't want to spin at different speeds. And it seems to be getting worse the more I drive
That ain't a trans mount that does that, a shelled limited slip govenor is about all that will do it.

That was my first thought. :grinyes:

HAve you visually inspected it yet? Anti-roll bars and torque arms make some noises in the banging catagory when they go bye-bye.

I haven't lifted it up to look at it yet, I peeked under there and everything seemed intact. I probably won't look at it until it warms up outside since, in the few days i've been driving my VR4, i've grown to want to drive it. So much less worry with a heavy AWD car in the snow, even if it is on summer tires.

That ain't a trans mount that does that, a shelled limited slip govenor is about all that will do it.

Yeah, from my own judgement that's what my first thought was. One-wheel peel that used to be 2 wheel peel + wheels dont want to go different speeds = diff./posi problem. Just wasn't too familiar with dealing with rear ends in general.

If the posi is shot (maybe, maybe not). You should really consider switching to a torsen.