theoUK

We've just reinstalled the diff into the 78, having rebuilt it with new bearings - retained the used ring and pinion however. The contact pattern looked good on both the drive and coast sides of the teeth - my first thread, with photos, is
here

One of the problems with this diff - before the rebuild - was a noticeable whine on the overrun. When it came apart, the pinion bearings were not too good, so I'd hoped that a new set and a decent setting up would have cured the noise.... Unfortunately not so! It's perfect under power, but as soon as it moves into coast, at above around 25mph, there's that annoying whine again.

I know setting up used gears can be a pain, but we opted not replace this set because they *looked* to be fine; no pitting or burning, nice smooth tooth faces. BUT they did make a noise on coast.
As mentioned, the new contact pattern looked good, but is it possible that these gears have worn to each other and are destined to make a noise, regardless of how "good" the pattern looks?? I wonder if they are likely to settle in after a while? My first thought is "no" but has anyone experienced any more bedding-in of used gears on newly set bearings?

I closed the backlash down a little on the rebuild, from over ten thou before, to between 5 and 8 thou as per the GM spec. Apart from that, it went back together with the same pinion depth, (different shim, to account for the difference in height of the old and new rear pinion bearings).

Anyone had a similar experience with used gears??

Cheers

Van Steel

I think it's pretty safe to say that if you had gear whine before the rebuild you will still have it afterwards. Not all the time but about 90% of the time.

Sorry Theo, I would have told you this before but I didn't know that was the reason you were rebuilding the diff.

mrvette

I don't know why, but it seems every damn diff I have ever messed with, except just carrier work, has been in a whiney state afterwards....
unless it's just the small pinion bearing....
and the patterns allways look good, and the backlash is fine....
but it allways whines....

fussy little bitches.....

wonder why??? anybody with any hard clues??

GENE

IRON WILL

I had the same problem with my 80, even though the differentials are different. I rebuilt my and changed to 3.73s. I had a good contact pattern on both sides of the gear. No noise on acceleration but It would whine when you were off the throttle. I took it apart and checked it over again, even brought it to a dealer to have there "world class tech" check it out. He said it was set up perfect. Just a noisy set of gears. I have sense gone back to the stock 3.08s for better fuel economy and set them up the same way. No noise at all acceleration or coast. It could just be the gears you are using. I have heard from some people that some gear brands and just noisy by nature. Also lower gears like 3.73, 4.10, 4.56s can sometimes make some noise. I don't know how much truth there is to that but thats what I was told. I would say that if the contact pattern is good both ways and the backlash is set within specs that it is just naturally noisy. I know how annoying that gear wine can be. Good Luck.

Van Steel

I don't know why but everytime we set up a diff w/new Richmond gears we would get a whine from the gears. Set up perfect patterns and still had trouble. The only gears we never have trouble with is U.S. Gears. Needless to say we don't use Richmond gears any more in vettes.

theoUK

Jeez, that's some bloody quick replyin' guys.... haven't you got anything better to be doing?! Actually, haven't I??!

Well, Dan, that's something to be "grateful" for - you can appreciate my biggest concern is that it's a result of some oversight on my part. Especially when, as you know, this job was on Phil''s diff and not my own.
Yes, it did whine just like this beforehand, I never really thought to mention it - the main object of this set up was to replace those dodgy side yokes and marginal bearings (the pinion rear brg had a very bent cage) so really, don't apologise, you guys have been fantastically helpful all the way through this - no need for apologies from you!
Phil seems fairly confident that the whine isn't worse than it was before - with tops off it's inaudible, even at 25 when the wind noise is low. Obviously the most important thing is that it's silent under power - a whine there would not be good. After all, on the overrun the only torque going back through the gears is what it takes to spin the driveline.

iron will - was it a new set of 3.73s that whined, or used?

Gene - I'd like to see some more technical info as to why the noise comes about too... this one's got me thinking...

I'll be very interested to see how the noises are when my 80 is back together - that is going to be on the used 3.55s, which look perfectly good in terms of wear. There was always a very slight overrun whine with them, too. Perhaps they'll retain that when they go back together, just like in the 78 I've just done.

Cheers for the responses guys

Theo

theoUK

Dan, do you mean a whine on the overrun or under power? I assume overrun?? And thats with new gears? Hmmm... I'm just trying to understand what's going on here, obviously on the overrun the torque transmission is going in the opposite direction. Think I need to find some papers on tooth profiles etc....

Van Steel

I was told that as well but I don't really know if it's true or not either. I was also told that certain gears are set up w/an even amount of teeth on the ring gear and pinion gear and some are done with an odd number of teeth. The odd numbered gears are supposedly stronger.

Fevre

Have Richmond 3.73 in my Formula and it whines pretty good on coast/deceleration, have read many posts about Richmond having this whine so it appears to be normal, believe it has something to do with the cut of the teeth making them stronger but noisey.

Van Steel

On both but mostly on coast.

IRON WILL

They were new 3.73 gears. I belive the company is Motive Gear.

Van Steel

We have also found that on the 80-82 diffs, if you replace the gears, you will most likely get gear whine as well. This is due to the posi units warping. We tested 5 diffs and we found that 3 of them had bad posi unit's. 1 of the diffs was mine. I put 3 sets of new gears in mine before I switched to a new posi. With the new posi, I had zero gear whine.

I have an 80 auto that doesn't get abused. If it does, it's not that often. Only when testing new products.

David Ey

What I have found is ....thats why you have loud exhaust.
If you have whine, work on exhaust.

Van Steel

A nice set of Chambered Exhaust should do it.

theoUK

David - trouble is you can have practically open headers and they still go much quieter when the car's on over-run

Interesting what you say about the posi units Dan, when you say warped, do you mean excessive runout on the companion flange for the ring-gear?

I checked the runout on the 78's ring gear and it was just within the spec, 3 thou, i seem to recall? Perhaps this is a contributing factor.....

Van Steel

yes sir

Andrew

I have low gears in my 79 and I can tell you that it will whine loudly from 50 to 30 mph. I've had several shops check it out and nobody has found any problems or given me a solution. I just live with it.

What is funny, several people hear the whine (mostly teens) and think it is a supercharger or turbocharger.

72-LT1

I was wondering how you heard the whine as well, I cant hear anything from the car when Im driving.

Andrew

If THEOUK is having the same problem, there is no mistaking this sound. If you don't hear anything (even over exhaust and a nice stereo) you don't have the problem.

theoUK

It's only audible when the roof's on, and it's very obviously diff gear noise. If you have any appreciable noise in the diff, then expect to hear it - after all, we're practically sitting on the back axle in these cars, and all that seperates the diff from your ear is a bit of fibreglass, some carpet ans two feet of air!