I just recently did a 800 mile trip in my 99 Z28 M6, and about 80 miles from the destination I notice that my rear end is leaking a little bit, and there's a slight knocking sound when I disengage the clutch while moving. I figured I could make and then put more fluid it in later. Well, about 10 miles from my destination is starts whining really badly, like multiple pitches at once whine. There wasn't really much I could do since I was so close and it was late, so I finished my trip.

I noticed my diff cover was bent a little (something had hit the bottom of my car, and I think it hit the cover), so I decided to go ahead and buy a new cover. I don't drive it for the time being.

I get the cover, and put it on. There seemed to be about half a quart of fluid left in the rear end. I fill it up with new fluid (80w90 synthetic), and take it for a drive around the block. Well, it still whines (it's really bad at about 50mph), and there is a knocking sound whenever I engage or disengage the clutch and it's in gear.


I have to drive another 800 miles back in a few days. Do you think that driving it will make anything worse? And what do you think is wrong with it? Should I wait to get it fixed after I get back (labor will be cheaper if I can't do it myself), or do you think I'd save money/time/aggrivation by getting it fixed here? I can do basic maintanence, but I don't carry around a lot of tools on long trips, so the more involved things I wouldn't be able to do.


***Oh, and I forgot to mention. I just had new gears installed (they're still 3.42's, although I regret it and should've put 3.72's) back in December (about 7 months ago). It had been running fine since then, except a little whine between 50 and 60mph. The differential had full fluid the day before, so I'm pretty sure I left with full fluid. The rearend is the stock 10-bolt that came with the car (although the gears are new).

 

Did you add the GM posi limited slip additive? It contains friction modifiers these cars need.

 

No, I didn't. There seemed to be a lot of mixed opinions on whether you should use the GM limited slip additive when using synthetic. I thought if I didn't use it, then it would only whine while turning. I read a GM bulletin I found from a link posted somewhere else (not sure, it was in the large jumble of searched stuff) that said it wasn't nessesary, just you'll get noise without it. Also the knocking is there. I'm avoiding driving it for now, though, until I figure out if I'll damage it by doing so. That wouldn't explain the clunking/knocking or extreme whining, though.

 

I had a gear installed a few years ago, When I got the car back it had a bad whine and a KNOCK. I took it back 2 times, they checked everything and couldnt find the problem. I had the gears replaced again with a different brand of gear(same shop). The whine was gone but I still had the knock. Just for the heck of it I put limited slip additive in it. The knock was gone and has never made that sound again. Its definately worth a try.

 

Oh wow. Well, I'll try that then. Where's the best place to get the additive? I'm assuming a GM dealer?

 

You can get it at autozone or advance auto. It really worked for me. Good luck.

 

Well, autozone didn't have it, so I went to a GM dealer and got it.

I added a bottle to my differential fluid and made sure it was full. I then drove around for a few miles at different speeds, and there is no noticeable change in the whining or the knocking.

So what do you think? I need to drive back home (~800 miles) in a few days, do you think it's safe for the car? And if you can think of anything else that might be wrong, please let me know. The car drives fine (if I was deaf, I wouldn't know something was different), but the whine is extremely loud and the knocking is still there when I engage or disengage the clutch.

Thanks

 

Have you checked the u-joints on the knocking problem?

 

The whining was the pinion bearings, which I just had replaced. Now the whining is gone but there is still a good bit of knocking.

I haven't checked the U-joints. I'm not sure what to check since I'm not really all that familiar with that area of the car.

 

Well, the car broke down after about 15 miles of driving :-(

So I had it towed back to the shop and they looked at it. Apparently there's no oil getting to the bearings. They went ahead and put new bearings in it again, though, but the mechanic says he thinks something's still wrong, considering what happened last time. He mentioned that he thinks it was shimmed wrong last time it was worked on. The car was worked on about 6 months ago and ran fine until this recent oil leak, so I'm not sure how that would be. I drove it today; there's a sound similar to the sound it had the first time I had it fixed (although much quieter; they replaced the gears and the carrier bearings that one time). There's also a strange ticking sound that's proportional to the speed I'm going (faster ticks when I'm going faster and vice versa).

I'm thinking about just going ahead and finding the money to get a 9", since it just seems I'm going to keep spending more and more on the current rear end (already have spent almost enough to get one, ~$1900 so far). Where's a good place to order a 9" from that is preferably inexpensive? What should I look for (what are the specs I need in a rear end for it to fit)?'

Thanks, any information would be helpful, even if you have a guess at why there's no oil getting to the bearings (and I'm pretty sure they weren't overtorqued).


Oh, I forgot to mention. This car is a daily driver which I occasionally take out to the track (circuit racing, not really much drag racing), when I'm done with it I'm expecting to put 500-600hp to the wheels. I think that information is probably important for the rear end choice...

I found this rear end on ebay, what do you think? Apparently this guy builds them and sells them.
http://cgi.ebay.com/ebaymotors/GM-Fb...QQcmdZViewItem