Clunking coming from rear

[Cutlass]

Alignment marks are a common practice when changing a pinion seal. The idea is to get the pinion gear, flange, and nut all back to the exact same place or slightly tighter to ensure proper pinion bearing preload is maintained.
FYI the pinion yoke shouldn't move at all (unless there's a bearing problem), so maybe you were just flexing the rear end bushings?

[jcws6]

Yeah, there wasn't enough movement to be noticable. I find it hard to believe that the rear end would just fail after under 25,000 miles, so I'm more likely to believe that someone was playing around inside the pumpkin at some point & F'ed something up.

Hopefully, I'll know for sure this week.

[jmdale1984]

I had a similar problem... turned out to be a tiny broken piece on the factory torque arm, it was very hard to see. Make sure you inspect it thoroughly.

[jcws6]

I took it the car to the transmission shop again for a gear oil change, and the third mechanic took a look at it. He said I have excessive play in the rear pinion yoke, and the ring and pinion are bad. Apparently, my driveshaft rotates too much to the left or right before moving anything.

I'd rather not replace the rear end until the fall, when I have more time, but I do want to drive the car during the summer. I'm debating on whether to pull the cover & check the gears myself, but I'm not sure what good that will do. Unless it's a super cheap & easy repair, I'd rather not spend the time & money to patch it up until the fall.

In the end, it looks like it's time for me to hunt for a new rear end. Thanks for all the advice, guys.

[Cutlass]

Well, thats called backlash and a lot of rear ends with some miles on them feel like they have too much backlash. You can measure and adjust the backlash with the rear cover off by using shims. I suspect if it really does have too much backlash then the gears are most likely shot. But I have a hard time believing they are.

[jcws6]

My car has very low mileage, so I'd imagine the backlash wouldn't be that bad yet. I might pull the cover & take a look for the hell of it, if I get a chance. I completely rebuilt a 10-bolt before, so I have an idea of what to look for, but I'm nowhere near a pro.

I'm guessing anything back there will require some serious work & won't be worth it on a 10-bolt. If I could fix it for under a couple hundred, I might consider it... otherwise it might just be a good idea to invest in the upgrade.

[jcws6]

As it turns out, the previous owner had gotten 4.10 gears installed, and they did a bad job. When I took it apart, the ring gear was so loose that I could twist the bolts out with my fingertips. The ring gear ended up shearing two teeth off the pinion gear, and that's where the noise came from. So, I decided to use a set of Motive Performance 4.10s & a Ratech rebuild kit.

I figured that since I've done a 10-bolt rebuild before, I could do mine for around $300 or so. Unfortuntely, I ended up destroying a seal installer I borrowed from AutoZone when I was pressing in some of the bearings ($55). Then, I cut my hand and had to take the half-finished rear end to a shop to get the backlash set ($100). Finally, I went through 3 pinion seals and one expensive mechanic visit to get the damn thing to stop leaking ($122). This is all funny because I had a shop willing to do the rebuild for $250, and I ended up spending $277 in frivolous bullshit. Well, it's not exactly funny to me, but irony's a bitch.

The total rebuild ended up costing around $575, which is damn near double my initial estimate. After 600 miles and a 250 mile Motive-specified break in period, it hasn't fallen apart yet. The noise is not horrible, but it's not as quiet as the old aftermarket gears, and there's some definite knocking at certain highway speeds. However, I plan on swapping this giant piece of junk assembly for a 12-bolt or 9-inch in a year or two. Even though the thing is technically better than stock (everything to spec, all bolts Loctited, solid pinion spacer, OEM seal, new crosspin), I'm not taking any chances.

[Szalkerous]

This is an interesting thread. I know I'm a bit late, but I thought I'd share a very similar story...

When I got my 99 Z28 off a used dealer (ack), it started to develop a traintrack sound in the rear end about a week into owning it. Having seen this before, I took the car out to a parkinglot and dumped 1st gear, not unreasonably, but hard enough to get some patches going. That's all it took to toss the entire ring & pinion. Had her on a flatbed back to the dealer with a story about trying to merge onto the highway. He had sold it as "immaculate"... yeah, sure it is. I told him unless a Chevy dealer did the repair, I wanted a full refund. Two days later and a copy of the work report from the local Chevrolet dealer, I had my pony back. Seems that whomever got at the rear end before me had used some off the shelf hardware store parts to rebuild it, amongst botching the job. I didn't get to see the damage, but I heard it. Sometimes it pays to lose a little rubber before the warranty runs out =)