I just finished rebearing rear differential on a 99 LS RWD 2 door Blazer, reused all gears as they were in good condition from what I could see no broken teeth hot spots etc. Gear pattern check on coast side looked good, backlash set at 7 t0 8 thousands. Felt good about it all. Reassembled and with rear wheels off ground ran speed up to 20mph nice and quiet , increasing speed higher than that and things werent so good heard a clunk and became noisy along with vibration. Brought speed back below 20mph and things settled out, Increased speed and got same results. Any thoughts ?

 

I would take the cover off and make sure everything looks ok. No ring gear bolts came loose or anything like that. If everything appears to be in order, I would take it for an actual test drive, rather than running it on stands. Sometimes the lash in the whole driveline can make it do weird things when running with no load.

If it still does it under normal driving conditions, you messed up somewhere. Which bearings did you replace? Just the carrier bearings, or also the pinion? Did you reuse the same pinion shim, or did you change it? How much preload did you put on all the bearings? Did you use a new pinion bearing crush sleeve?

Also, make sure the u-joint is properly installed in the yoke. If a clip is missing, it can get off center and cause vibration.

 

Tom A
Thanks for your reply. I did an open an inspect today and all looks good checked torque on ring gear and carrier bolts still both at 60 ft lbs. I replaced all bearings did reuse original shim on pinion gear 31 thousands as the gear pattern looked good to my eye after several attempts with other shims. Preload on pinion gear is 12.5 inch lbs range for new bearings 10 to 15. replaced all carrier shims didnt put back original cast iron. The rotational torque needed once carrier was in place and torqued down with proper backlash 7 to 8 thousands was 20 inch lbs continuously rotating the gears. Must be some preload on carrier bearings as this value was greater than preload on pinion gear.
If the pinion depth is bad I would think regardless of speed that would be be an issue.?
Did take vehicle for ride and all was nice and quiet until speed got up above 20 25 mph then things got loud.
Breaking it all down again as you mentioned I screwed up some where, will replace u joints both ends of driveshaft see if that helps
Again thanks for your insight

 

If you end up taking it apart and checking the pattern on the gears again, post pictures here and we can give you opinions (though it sounds like you already know what you're doing).

 

After re-opening the differential I removed the carrier and sure enough, I screwed up. The carrier bearing on the passenger side was not fully seated. Took care of that and reassembled it. Replaced u joints on driveshaft also. Big difference. The vibration disappeared however I still think something amiss at speeds above 30mph. Not sure if its just tire noise? the best description is a heavy humming sound. Being a 2door and 2wd the differential is right there behind you and things sound good during acceleration and deceleration no clunking or other noise that is noticeable. Thinking gears maybe just worn out or the pinion gear is too close to ring gear reused original shim This all started from loss of oil due to seal leak that went unnoticed until there was no turning back. Pics of gear contact on coast side.

 

There's only one tooth in that picture (at the top) that has a good, readable pattern, and it looks like the pinion is a little deep, but probably not enough to make it noisy. The gears don't look badly worn, but wear can be pretty hard to see. Any chance you have a bad axle bearing? Does it sound like it could be coming from one side or the other?