Diff whine… did I cause it?

[e30jake]

I replaced my 2.93 open diff today with a 3.46 LSD from a parts car I had. No clue how many miles are on it, just that the car was maintained by an enthusiast from 1992-2006 before it was wrecked, that it leaked badly from one of the output seals. I took it apart to reseal it and got it back together successfully. I fill it with Royal Purple 75w90 and turn it to make sure everything is good. It turns a little harder by hand than the other diff I have sitting in the shop and the one that comes out of the car. Whatever, the seals are new, maybe that has something to do with it. I put it in the car, seems fine for the first bit of driving. I hit 35 mph and boom, the whine becomes very noticeable. I should note that my back seat is currently out. It gets higher and louder with speed, and is a constant whine. Acceleration, deceleration, coasting, doesn't matter. Above 35 mph it's there. From what I have read it sounds like the bearings could be on their way out. When I did the seals, I took both output shafts out at once and had the gears inside just sitting there. I carried it inside like this and the gear rolled around a little, but I couldn't imagine I damaged it this way. I assumed it would not matter since the output shafts would center it when I reinstalled them, but could this have messed with clearances or done anything to be causing the whine? Or is this a clear case of bearings based on how much more difficult it was to turn it by hand? Thanks in advance guys.

[Jaxx_]

Did you put any cheese in your diff? I heard it goes well with whine..


Okay but seroiusly, I imagine if you didn't confirm backlash it could cause this whine. I'm not sure what you did exactly when 'resealing' the diff, but if you didn't measure, it could be out of spec.

[redlightpete]

As long as you put the output flanges and their shims back on the same side they came from, the preload and ring gear position should be unchanged. These diffs do wear and get loud. When I redid my 300k diff, the pinion bearings were especially worn. Maybe put the back seat in and see how loud it still is. Some 75w-140 fluid might be a little quieter.

[e30jake]

Did you put any cheese in your diff? I heard it goes well with whine..


Okay but seroiusly, I imagine if you didn't confirm backlash it could cause this whine. I'm not sure what you did exactly when 'resealing' the diff, but if you didn't measure, it could be out of spec.

New output seals, snap rings, etc. I guess resealing is a little bit of a stretch.

As long as you put the output flanges and their shims back on the same side they came from, the preload and ring gear position should be unchanged. These diffs do wear and get loud. When I redid my 300k diff, the pinion bearings were especially worn. Maybe put the back seat in and see how loud it still is. Some 75w-140 fluid might be a little quieter.

90% sure I put them back on the same side, but I guess that is a possibility.


Any input on why it would be so hard to turn by hand? I turned the old one today and it turn with about half as much effort as the one I'm having trouble with.

[redlightpete]

Are you turning one output flange? That would be a lot easier on the open diff.

[e30jake]

Are you turning one output flange? That would be a lot easier on the open diff.

It was much harder to turn the input flange too.



After some more research, I have an idea as to why it is turning so hard. While it was apart i cleaned all the parts up as much as I could. The shims had a little bit of rust, so I used a little sandpaper to get rid of the rust. I didn't think much of it, but I may have taken enough off that I increased the preload on both sides. If the bearings were pressing too hard, it seems like that could cause it to turn so much harder, right? Any thoughts on this? Would that cause a whine?

[redlightpete]

Unless you were sanding with a machine, I strongly doubt you made those big shims any thinner. If you can round up the factory specs, you could see whether the resistance you have is still ok. Too much preload shouldn't cause immediate noise anyway. I think it is more likely that this is just a loud diff.

[Wanganstyle]

95% chance if the diff is noisy:

Pinion bearings & races are dying and alerting you; perhaps it tried to alert the prior owner as well and that's why it was sold

if you have tampered with the settings by removing the output flanges its possible you could have changed Left and right shims; one will be thicker and one will be thinner; gap setting def. can be messed up by this.

[redlightpete]

You could compare the amount of backlash at the input flange between the two diffs. It should be similar. If you accidentally swapped shims the backlash could be off. Hopefully you can turn the driveshaft to check diff in the car.

[e30jake]

You could compare the amount of backlash at the input flange between the two diffs. It should be similar. If you accidentally swapped shims the backlash could be off. Hopefully you can turn the driveshaft to check diff in the car.

I'll check the backlash try switching the shims and see if that changes anything. If not, I'll take it back apart and make sure the bearing races are seated all the way. When I pressed in the new seals, I pushed at least one of them to the edge of the end cap. I pressed it back before I reinstalled them, but I wasn't that careful. If they aren't all the way in the end caps the preload would be increased (right?), or would they be pushed back out by the bearings upon installation? I'm hoping to get into it this weekend.

[redlightpete]

If you pushed the bearing race out and didn't get it fully seated back, I think that could account for your preload being too high. Unfortunately, that probably wouldn't fix the noise issue, but maybe. I'd agree with wanganstyle that the most likely noise issue is the pinion bearings.