Rear End Vibration. Need Advice

[chevy8806]

So I recently acquired this Blazer and I have been slowly nursing back to health. Without going into a long and boring back story, I have a vibration in the back end that I need help with. The vibration gets worse with speed and under load. At freeway speeds and when I lift off the throttle the vibration reduces considerably.

First, I determined the rear driveshaft had some issues. The joints at the yoke had excessive play as well as one of the weights was missing. I replaced the entire driveshaft assembly and test drove. This helped but the vibration is still there.

Secondly, I took the rear diff cover off to see if I could find any clues. I noticed that the oil was clean but it had a lot of tiny air bubbles. Also, the magnet was clean and had no evidence of metal shavings. I checked the vent tube and it was clean. So to try to figure out where the air bubble were coming from I checked the axle seals and bingo!

Question: Could this vibration come from one or both of the axles and the bearings? Since I have to replace the seals I mine as well replace the axle shafts and bearings. I can not think of anything else it could be. What do you guys think?

 

[Horns]

It may seem simple, but have you thrown the tires on a balancer?

 

[98_k1500]

I actually have had a bad rear wheel bearing on one of these trucks. The oil gets aerated from the gears spinning inside there. Google a diff with a clear cover if you want to see a spectacular marvel of oiling technology. My axle seal was not leaking, but i had a rear wheel bearing bad. You could shake the tire up and down with a pry bar (like checking a ball joint on the front). It did not vibrate however. It just made some god-awful howling noise. Best description i can think of for it is 100,000 bullfrogs croaking constantly. It was pretty loud. I'd be looking into a bad tire or excessive runout in a wheel. Pull the brake drums and clean up the axle flange and the drum surfaces if your tires/wheels check out ok. Make sure they are seating together correctly.

 

[ChristGilley]

I actually have had a bad rear wheel bearing on one of these trucks. The oil gets aerated from the gears spinning inside there. Google a diff with a clear cover if you want to see a spectacular marvel of oiling technology. My axle seal was not leaking, but i had a rear wheel bearing bad. You could shake the tire up and down with a pry bar (like checking a ball joint on the front). It did not vibrate however. It just made some god-awful howling noise. Best description i can think of for it is 100,000 bullfrogs croaking constantly. It was pretty loud. I'd be looking into a bad tire or excessive runout in a wheel. Pull the brake drums and clean up the axle flange and the drum surfaces if your tires/wheels check out ok. Make sure they are seating together correctly.

Exact symptoms of my front end wheel bearing too


Sent while pulling out a Ford

 

[chevy8806]

When i bought the truck it had tires on it dated back to 1997 and even though they had good tread, the tires were soo dry rotted i did not trust them. So I put some worn Michelin take offs from another truck just to have newer tires. The balance on the tires was not out of reason. The vibration existed before and after swapping the tires out. I could rotate the rear to the front and see if the vibration changes.

 

[aaronb]

Check for play in the pinion. also check for play in the output shaft in the t case.

 

[dillhamm]

This might sound weird but I had this problem right before my tansmission went out. My theory is that there wasn't enough ATF or the pump wasn't putting enough pressure on the clutches to hold them solid.