rear axle bearings, vibration question

what exactly are the rear axle bearings and can they cause vibration at higher speeds? i have a '00 blazer LT that you can feel vibration in the rear at any speed over 40 mph. no vibration in steering wheel and cant feel it that much, but you can definitely hear it and it can be felt more at higher speeds, then kinda goes away around 75 or 80, have had the following fixed to try to stop the vibration:

-checked front hub/bearings, no play
-replaced u-joints
-replaced tires/balanced twice
-alignment done
-checked tie rods/idler arm/front steering components, all tight
-checked, topped off rear diff fluid
-balanced driveshaft
-checked rear wheel bearings, no play
-checked rear/front shocks and springs, were good

so does anyone know what is left to check? im at my wits end with this problem!! :(

I doubt if it's your rear axel bearings. I would more suspect a bad/bent drive shaft or a bent axel shaft with the symptoms you describe...

Usually with a speed cauised virbration like that I would be looking at the axel shaft. Granted, a bent axel shaft could cause one of the axel bearings to go bad, but it's unlikely.

When they replaced the u-joints, did they replace both or just one?

Also for giggles, I would have the motor mounts checked.

what exactly are the rear axle bearings and can they cause vibration at higher speeds? i have a '00 blazer LT that you can feel vibration in the rear at any speed over 40 mph. no vibration in steering wheel and cant feel it that much, but you can definitely hear it and it can be felt more at higher speeds, then kinda goes away around 75 or 80, have had the following fixed to try to stop the vibration:

-checked front hub/bearings, no play
-replaced u-joints
-replaced tires/balanced twice
-alignment done
-checked tie rods/idler arm/front steering components, all tight
-checked, topped off rear diff fluid
-balanced driveshaft
-checked rear wheel bearings, no play
-checked rear/front shocks and springs, were good

so does anyone know what is left to check? im at my wits end with this problem!! :(

I know you stated that you already replaced your U-Joints but I'd suspect that they are the culprit. If they weren't installed properly they would cause the very symptoms you are describing. :rolleyes:

It could be the rear. If your truck has a posi in it, the posi could be bad. That was the cause of the vibration in his full size truck. Also if the pinion on the rear has play in it, that might be the problem.

I doubt if it's your rear axel bearings. I would more suspect a bad/bent drive shaft or a bent axel shaft with the symptoms you describe...

Usually with a speed cauised virbration like that I would be looking at the axel shaft. Granted, a bent axel shaft could cause one of the axel bearings to go bad, but it's unlikely.

When they replaced the u-joints, did they replace both or just one?

Also for giggles, I would have the motor mounts checked.

they only replaced the rear u joint, said the front one was good.

Did any of the fixes seem to make it a little better?

Have you checked your transmission and transfer case mounts?

honestly... nothing has improved it at all. :( do you think it could really be the front u joint on the driveshaft?

What about an alignment?

yea like i said above i had the alignment done, actually twice already to no avail.

Could be the inner rear axle bearings. I currently have this problem. The rear hums at higher speeds, but I don't notice any vibration. The hum goes away at about 70.

i really think its my driveshaft. anyone know where i can get a new one? or can this one be rebuilt?