Diagnosing Rear End Noise 2003 Suburban

Dang, carrier bearings are essentially a rebuild.. You'd have to reshim swapping bearings correct?
Not necessarily. I'd press on new bearings using existing shims and run a pattern. 90% chance it'll read good enuf, and with a used gearset you can't expect perfection

BUT if a carrier bearing is making noise a visual should reveal something. Pull the carrier (mark cap positions of course per SOP), wipe down the bearings and races and look for any flats, irregular wear, galling, brinelling, excessively loose rollers etc

Heck I guess you could first put an indicator on the carrier and use a pry bar to see if you can get it to move any. Lack of movement wouldn't prove bearings are ok but the presence of movement proves a problem right there.
 
You specifically suggested to add 2 oz of limited slip additive in your 1st post, which is exactly what GM says not to do. I said this is a bad idea, which is it, as it goes against exactly what GM recommends for the G80 locking diff. Regardless of what you do with your vehicle, adding limited slip additive is a bad idea on the G80 locking diff.
I did say that but it was for his rear dif that was making noise. I did not add FM to the Redline 75W90 in my Colorado. Sorry for the confusion.
 
Have a differential shop nearby? They may be able to better evaluate. My F150 made a strange squeak for years only when the diff was complety warmed up. Ended up being the plastic pinion seal guard. The diff. Shop diagnosed and cut off for free. He said a lot of Ford owners complain about that. I never would have guessed
 
I topped it up until it dribbled out the fill hole and so far so good. Its not totally full since I was slightly tiled forward. I crawled under it on a level street and its just below full. I have been driving it around and going to the physical places I normally was hearing the noise. So far it hasn't reproduced. I will continue to listen. About to drive a lot for xmas so will report back if anything changes. Lesson learned, top it off like it was when I drained it.. not following the book next time. The fluid I used was the same ac delco 10-4016. forgot how potent the stuff is.
 
Interesting that a slight adding of fluid seems to have solved this one, one can only hope things are always that cheap and easy.

For the record G80 has been the code for a limited slip forever, like at least the mid 70's probably earlier. For GM to decide to just call the eaton gov lock "G80" was a colossally ignorant idea, because people now think any G80 is a gov lock and it isn't.

If it were mine and the noise came back I would figure out what differential it actually has and go from there.
 
Interesting that a slight adding of fluid seems to have solved this one, one can only hope things are always that cheap and easy.

For the record G80 has been the code for a limited slip forever, like at least the mid 70's probably earlier. For GM to decide to just call the eaton gov lock "G80" was a colossally ignorant idea, because people now think any G80 is a gov lock and it isn't.

If it were mine and the noise came back I would figure out what differential it actually has and go from there.
People very often overlook simple solutions, and just throw parts at their problem. In this case, I don't know of anybody except the factory that "low" fills their differential regardless of what the owner's manual says. That said, the only thing different in the OP's scenario was that the diff was full like it should be when he drained it, but he refilled it like the manual says, which is low, then he had a noise. People were suggesting additives, diff rebuilds and bearings and such while overlooking the obvious, it was low on fluid. Happens ALL THE TIME!
 
Years ago there were issues and theories that some gaskets blocked some holes in the diff housing that facilitated flow of lubricants to the axle ends. I recall in day the late 90s/early 00s this was often debated.

Is that still a thing? Could flow be blocked?

Also, 90 wt got relegated to the lower end of a range. If what was in there before was thicker, it could have attenuated sound.
 
Gasket could be contributing. I put a felpro on it that they claim is a match, but the holes were not perfectly matching. I ran it anyways since its all I had. DIdn't think about that until you mention it.

Yes original owner, it wasn't serviced as much as it should have been. Inherited the truck.

The fluid was a bit dark from age, but it was clear and clean.
 
That is my understanding, the service data doesn't specify it and I didn't put any in.
 
Years ago there were issues and theories that some gaskets blocked some holes in the diff housing that facilitated flow of lubricants to the axle ends. I recall in day the late 90s/early 00s this was often debated.
Not saying this wasn't a thing, but I've never heard of such a thing. Lubricant flow to the axle bearings is through the axle tube, not the diff cover. BTW, Anytime I do a diff oil change I drive to where I can park on a good side slope for a few minutes one way, then turn around the other way to ensure the axle bearings get a good flush of new oil. Probably not necessary but it makes me feel better.
 
Not saying this wasn't a thing, but I've never heard of such a thing. Lubricant flow to the axle bearings is through the axle tube, not the diff cover. BTW, Anytime I do a diff oil change I drive to where I can park on a good side slope for a few minutes one way, then turn around the other way to ensure the axle bearings get a good flush of new oil. Probably not necessary but it makes me feel better.
This was primarily initially noted on caprice cars IIRC, but the gaskets were interchangeable, with diffs in the S-10 ZR2 and I think some C/K trucks (?). Just made me think about noises because lack of lube going through these holes and down the tubes could be an issue. For a while there were lots of gaskets that blocked the holes, nowadays you see more with the holes, but if it wasn’t right in the early 00’s, when this was happening, the early damage could have been done, and now long term wear is showing up. From the archives:

Subject: rear end problems & outer bearings
Date: Mon, 15 Nov 1999 09:58:38 -0500
From: Ken Rolt EMAIL]>
To: 9C1 Mailing List EMAIL]>, 94-96 B-Body EMAIL]>,
91-93 B-Body EMAIL]>, "91-96 wagons I.G.B.A." EMAIL]>,
NAISSO list EMAIL]>

To be brief and for those of you new to the subject, the GM 8.5-inch rear end is lubricated by gear oil (lube). The lube is intended to both lube and cool the differential (ring and pinion gears, sidegears, axle splines, L and R diff bearings) as well as the L and R outer bearings that are next to each rear brake.

How the differential is coated with lube is easy to see: the fluid level in the rear end is such that the ring gear dips into the fluid level and splashes it all over the interior of the rear end.

How the lube gets to the outer bearings is NOT easy to see, but easier to describe. The rear end differential cover has a "shelf" stamped into it, so that lube flung from the ring gear to the inside of the back cover, gets redirected by the "shelf" to both the left and right sides of the diff housing. If you had the rear diff cover removed, you would see two large circular holes in the axle housing. The shelf is designed to direct lube into each of these two holes. The lube then pours onto each axle shaft. Most of the lube then drips off the shaft(s) and onto the floor of the axle tube, but some of it still clings to the axle shafts. The rotation of the axle shafts causes the clinging
lube to creep along the axle shaft inwards (back to the diff) which helps lube the side gears, and the other part creeps outward on the axle shaft toward the outer bearings. That's how it is *supposed* to work.

BUT GM stopped, a handful of years ago, using a diff cover gasket with mating circular lube holes so the lube path to the outer bearings via the axle shaft path was eliminated. Only random splashing within each tube, or frequent vehicle turns, would cause the outer bearings to be lubed often.

What is the result? The outer bearings get too hot and they begin to heat discolor the hardened bearing surface on each (outer) axle, and eventually the axle shafts become pitted. Only then would be BEGIN to hear funny rear end noises, so this is one of the problems that needs to be checked BEFORE you have a problem.... especially on a used police car like the 9C1.

When I bought my '94 9C1, I had the axles pulled and checked. The driver's side axle was ok but the pass side was pitted at the bearing surface. I have heard worse stories where the axle actually becomes grooved. In my case, I had both
bearings and seals replaced, as well as installing a new pass side axle. I made sure that the dealer used a gasket (Felpro RDS 55028-1) with holes to allow the axle shafts to be properly lubed. I have since drained and refilled the diff,
and did my own gasket install. There is also a new GM gasket which supposedly allows the lube holes to be partly or fully opened, and lube correctly, but I have yet to install it myself. Joe Nerz's post on the new gaskets is attached below. I believe that Joe Palmer, among others, put pix up on the web comparing the gaskets (old GM, Felpro, and new GM).

In the crude survey I did over a year ago, among 9C1 owners that did any rear end work, *most* of the time it was the passenger side outer bearing and axle that was shot. I surmised, from working on my own car, that the reason is that
the pass side bearing is much more lube-starved than the driver's side. This is due to the ring gear being located on the driver's side of the car centerline, so it can much more easily splash-lube the driver's side outer axle but it cannot do the same for the pass side. Why? Because of the large obstruction in the way: the differential itself.

---- Tip for New Owners ----

If you have a B or D-platform car (Caprice, Impala, 9C1, Roadmaster, Custom Cruiser, etc) and you've never checked the rear end DO IT NOW. If you are tool handy, study the FSM and do it yourself. I'm not a rear end expert (Roswell, no
funny remarks!!!) so I had someone do the work for me the first time. The passenger side axle is the one that should be checked first, by draining the diff, unbolting the diff cover, removing the c-clip for the pass side, and then removing the pass side axle to inspect the bearing surface. If it looks ok,
then the driver's side is probably ok too. If the axle shows any sign of stress or grooving, it will have to be replaced. In that case, you should have the driver's side checked as well, and both the seals and outer bearings should be replaced. That would also be a good time to have the rest of the rear end
checked for problems.

If you have a G80-equipped car, this is also a good time to have the posi checked out and possibly rebuilt.


Other items relevant:

1. if the diff fluid is low, old, or both, inadequate lube and cooling will result. This would affect the whole rear end, not just the outer bearings.

2. a leaky pinion shaft seal is often the cause of low diff fluid, and hence heat-related failures.

It has never been proven what causes the axle and bearing failures on B and D cars; the two main clulprits are the leaky pinion seal and the lack of lube holes in the rear end diff cover gasket. Both can cause problems.

But I'll put my money on the bad gasket, because I've seen/read failures on plenty of cars with good pinion seals and adequate rear end fluid. Hence outer bearing problems and axle bearing surface failures can only be caused by the
lack of lube, especially on the pass side.

HTH. - Ken mailto:[email protected]
 
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