2002, 2-door, 4x4, S10 Blazer

I've got a really difficult to diagnose rear differential noise and vibration I've been trying to solve for 6 months now.
It started back in December 2020 when I'd only hear a subtle howling while only turning right. I've been taking my time troubleshooting this, but I keep hitting dead ends and the noise just keeps getting worst.
Before the noise started in December 2020, I serviced the differential for the first time at 165,000 miles, changed the fluid, and changed out a bad axle seal on the right back in June 2020. Almost 5 months after that, it started making noise that took me a long time to narrow down it was in fact the differential.

I had just recently opened the rear end again to check things out. Ring gear is good. Carrier is good, Pinion is good. No odd discoloartion or wear. The axle bearings were indeed going bad, so I replaced both of those and put new seals on.
I was pretty sure it was these bad bearings because that's what the noise sounds like.
After putting it back together and doing a test drive, the same noise and vibration is still there. So the bad axle bearings were not the cause of the sound.

I've done all the simple solutions short of a full differential teardown and rebuild. I took it in to my regular mechanic and he checked it out, inspected the inside, and etc...
My mechanic says the next thing to do is to drive it regularly for a bit longer then bring ti back in to inspect the gear oil and see if there's any metalic flakes in it.
He says teh next thing to try from there is a rebuild kit.

What do you guys think? Have you had any strange noise problems with these 10 bolt, 7.625", auto locking differentials?

 

To be clear here...you have the G80 diff? If so, do a YouTube search on them to see all instances of the G80 destruction.
Might be time to invest in a new limited slip diff...Yukon has a nice drop in.

 

How did the bearing surface on the axle shafts look? Usually when a bearing fails, it takes the axle shaft with it.

 

What Tom wrote above. If by chance you have spacers on the rear, these tend to wear out the axle bearings and take the axles with them.....actually I think anytime the axle bearings are bad/noisy these take-out the axles. Check to see how much play there is between axle and bearing. Have to remove the caliper to do this.

 

Axles were in good shape. The bearings had not failed catastrophically yet, but they were on the way out. I had my machanic take a look at everything to make sure nothing was going over my head. He added this gear oil conditioner that GM recommends and since then it's been making less noise, but it's still there. I don't hear it as much now coasting down hill, but it's there on right turns when the weight starts shifting.

 

I guess it could be one of the diff carrier bearings...but these seldom fail. It may be the auto locking (G80) components...not able to help any here...have never worked on one.

 

I've also been doing some more reading on bad U Joints. I asked my mechanic to check them, and he says there's no play, so they're good. But I was reading that U Joints can go bad and not have any play in them. I'm still running the factory OEM U Joints here that are 20 years and 180,000 miles old. If there are bad, would that be causing extra wear on the rear differential causing that noise?

I'm bringing up U Joints because I drove it out of town recently on I-95 along the east coast and I got a lot of rear-end shaking and vibration driving along anywhere between 60 and 75 MPH. It settled down some on smoother parts of the road, but it felt as bad as it was before I rebuilt the whole front-end. I thought I had finally settled this shaking/vibration problem once and for all, but it keeps coming back.

 

A bad u joint caused it to break off the rear on my blazer. It happened on a trip from Ontario to Florida, as soon as I got into Pennsylvania...

Edit: **Rear yoke and bearing on the diff and driveshaft had to get replaced **

Oh yea, was towing a camper too...

I would replaced the factory ones for comfort, and they aren't that pricey...

Any wet spots coming from the yoke area on the axle?

 

Could not hurt at all to replace both front and rear U joints. If you do the work yourself be advised that they are glued-in; heating with a torch get the glue to come out and then you can press the U joint out with one of those rental/loaner press tools. Probably still a YouTube video out there on these.
When I did the U joints on mine, I had both driveshafts re-balanced at a local shop just to be sure.