I have a '97 Z A4. I have set up the gears in my rear end twice already. Both times in my opinion, some thing is just not right. My car used to have 2:73's and a few years back, I went to 3:73's. Upon de-celleration, I get a whine - which I'm not concerned about....a lot of people have that. But upon coming to a stop, I get a rubbing/grinding noise coming from the rear at about 5-10 mph. So, a few weeks back, I pulled the rear out to re-do it again, thinking something was wrong. Well, we re-shimmed the posi unit a few times and got it real close to what the gears called for. On my ring gear, it was stamped 8 thousdandths. So, we moved different shims back and forth, and got the backlash real close at 9 thousandths and called it good. We put it back together, re-installed the diff in the car, and no help at all! The posi unit was a little tough to get back in there though the last time. We had to gently tap it with a plastic hammer to get it to slide in. Is that normal? Or should the unit just slide right in there? Also, the pinion depth in set to spec....I can't remember what exactly that is, but I do remember getting it perfect to what the spec on the gears called for. I am using the Mobil 1 synthetic and limited slip additive also. I have tried a normal blend 89/90 gear oil and no help there either.

I was also talking to a friend of mine and he had said when he set up rear ends for street, he set the backlash loose, as in between 10-20 thousandths! That seems a little loose to me. Any opinions on that are welcome.

So, what should I do? Should I pull it back out, re-shim it so its more loose? Or, tighten it up some more?? I'm at my wits end with this rear end and I just want to do it one more time and get it right! And I'd really rather do this myself without taking it to the dealer or something.

 

ok first, don't shim it to 10-20 thousandths..it'll break really fast. Second you're going to have to drive it a while now to try and salvage the gear. My first question is did you break it in properly?? 30 min drive then cool, repeat twice, then figure 8's for 30 min, then cool, then repeat in opposite direction, then cool?? If you did then weak gears wouldn't bee a worry. But if it was really bad and you kept driving..ie. more than 500 miles then you probably need a new gear set. You probably wore the pattern in and now no matter what you do it's going to make noise. And yes sometimes you need to coerce the diff's back in and out for that matter. Good luck.

Chris

 

I did break it in. I wasn't hard on it all after installation. I had a to wait a week or so till I got my PCM reprogrammed any way, so I didn't want to beat on it too bad right after installation. I just drove her normal in the immediate days afterward. Good suggestion though.

What do you mean by 'drive it a while, and salvage the gear?'

 

you may get lucky and after awhile of driving the noises may subside. If that happens you have esentially salvaged the gear. when you set up a gear incorrectly and drive over 500 miles it develops a wear pattern. You may get lucky and be able to save it, but most likely you'll have to get a new one. The biggest deal is letting a new gear cool off after it's installed (it allows the metal to harden). Either way i hope you get it fixed, rearend whine really sucks.

Chris

 

the 1st thing you did wrong is you broke it in with synthetic oil, i know richmond recomends it but i have seen scored gears from it, it doesn't protect the steel like mineral oil will buring breakin and wont disapate the heat and fosfait coating. secondly you did not note what brand of gear you are using, is a GM, Motive, Strange, Richmond?
the Gm's should not make any gear noise and should have been set-up with a .034-.036 pinion shim is average, with the aftermarkets they should set-up with about .038 or more. richmonds usually quitet up with more backlash around .009-.010
you note that the noise is on deceleration,sounds like it might be too deep"to much pinion shim".

 

I am using Richmond Gears. Maybe I wasn't clear before....I am NOT concerned about the whine - as I hear a lot of people state that it is normal. What I am concerned about is the rubbing/grinding noise upon coming to a stop. The backlash is currently at .009. I could double check the pinion depth one more time just to confirm.

But nobody can seem to answer whether or not its normal to have gently tap the posi unit back in with a hammer, or should it just slide in there? Even though my backlash was right, it just seemed really hard going in there.

What about heat? If I drove the car for a while, parked it....if something is wrong, would the diff be a little hotter to the touch than normal?

 

What does your wear pattern look like? Get some of that stuff and rub in on your ring teeth and rotate the diff by hand and see where the pinion is actually contacting the ring.

 

I think you need to check the pinion (sp), You did use a pinion shim right? Normally about a .029-.032 is needed for the pinion. Make sure when you run the pinion in it is TIGHT there should be no up or down movement on the yoke, take that air gun and bump it till you get no play. then run you pattern see what you need then fine tune it with the carrier side to side. my break in is 5 mins on the lift just to get everything to mesh. You might have to use the stackable shims for the carrier shims insted of the solids. keep us posted.

 

The differential is currently back together and in the car. I took it for a drive two days ago and found that my problem still persists. Which is when I posted this thread. So I don't know about the wear pattern....I'd have to look at it when I pull it out AGAIN. I just wanted to get some facts and things to check before I did that. Because before this post, I was ready to take the darn thing to the dealer and have them deal with it. But I think I'll try and check some of things mentioned here before that happens. Thanks guys.

 

Personally, I don't think it's your rear end at all. Your rear isn't the only thing that can generate sound. And usually, you'll only get that whine while accelerating or running just enough to maintain speed. I think you need to look at your tranny or front yoke of your driveshaft. Why do I say this? Cause I just trashed my yoke this week at the track. Twisted all the splins in it. Sounded like the rear. Whine on deceleration only. Low grinding noise when almost stopped. May not be that for you, but just more input for you. Mine made all that noise in any gear on decel, any rpm, any speed. Also did it in neutral. Only difference is I have a 6spd, but you still have an output shaft and front driveshaft yoke also. Can't see it being your rear gears, especially considering how many times it's been set up. Also look at your axle bearings if you haven't already. Does it do it in every gear (shifting it manually and decelerating? Does it do it in neutral? Any speed? Just curious. Let us know what happens.

Ken R.

 

I *think* I know the type of sound you're talking about when the car slows right down, almost to a complete stop. Unfortunately (maybe) I doubt there's much that can be done. Given my own experience with a bad set of Richmond 3.73's, I'd say there's a good chance it's simply in the cut of the gears. My 3.73's whined like there was an ambulance chasing me, and this was from the very first drive, and again after being "re"-setup and double-checked again! The pinion and backlash were all within spec, they just whined. Now my Richmond 4.10's are silky smooth, almost as quiet as the factory 2.73's.

I'd be willing to bet it's the gears.

Oh yeah, as far as the carrier being tight to put back in, they should be a little "snug", because if it just slides back in, then there's no preloading on the bearings, and the carrier can shift side-to-side while you're driving (undesirable if you ask me).

 

Ken -
Good response. When I had had the rear apart a few days ago, I did inspect the axle bearings. They were okay. I had one leaky axle seal on the driver's side, so since I was doing it, I replaced both the driver's side and the passenger's side. I don't know if the car makes the noise in neutral. That's a great idea, and I never thought to check that. The noise does not occur in every gear nor at any speed. It seems to just occur in 2nd or in 1st upon almost coming to a stop. At highway speed, all is quiet. I will try the neutral idea when I get home from work. And maybe I'll get my driveshaft checked out as well. It might be easier to try that first before I pull the rear out again.

Capn Pete-
Its a very good possibility that it is in fact my gears. I have not omitted that possibility. I hope its not, of course. But, I think I've come realize if that ends up being it, I will replace the gears with GM's or something of the like.
Thanks for the reply.

 

The more info the better. What gear, what speed, what rpm, in neutral, accelerating, decelerating or part throttle. All can be helpful. You can also pull your driveshaft, put the rear on jackstands, and run it in gear and see if it's still noisy. If not, then that rules out the tranny. Be sure to block the front tires good and watch out cause you'll get some tranny fluid coming out the output of the tranny. But you only need to run it for a short time to check. Lay a rag or someting on the ground to catch the fluid and top it back off when your done. Pete is also right, Richmonds whine. I had 2 sets and both whined. 3.73's and 4'10's. I finally went to GM Motive 4.10's and they were quiet. But my Richmonds never whined when decelerating. Hope that info helps.

Ken

 

Okay guys....here's an update....

I drove the car this evening and found that I DON'T have the rubbing/grinding noise upon slowing down in neutral. Its totally quiet and normal sounding when coming to a stop IF I have the car in neutral. Now, if I put the car back in drive, it will commence the rubbing/grinding. So, what's the deal? Does that narrow the problem any? Driveshaft???

 

What about the whine? That still happen in neutral or that go away too?