At 50 moh the rear starts to shake. Felt like a bad balance. The tires were worn and due. So I but on a new set of tires. Vibration is better but still there. It continues to about 75 then smooths out. I took off both the rear tires and removed the brake drums/ Grabbing the axle I get a slight up/down movement from the assembly.

IS this normal?
Is this a bad bearing?

 

Sounds like the bearings are bad to me.

 

The tire shops says their good.
How do I confirm this?

 

I've never seen a bearing go bad enough to cause vibration without making a LOT of racket before as the metal gets ground to hell.

I vote for some other balance issue at the tire/brake area.

 

^^ This is also true.

 

I get no noise. Just vibration. Have for two sets of tire, multiple balancing.
And at least 1 brake job. Unless the drums are WAY out of balance I see no way for the brakes to cause vibration.

I'm ruling out the drive axle because it is smooth up to 50 MPH or so, worsens thru 65 and goes away at 70+. If the axle was out of balance the vibes would get worse as it increases in speed.

Ive seen the tires on a balancing machine and they turn true. So its not the rims. If I rotate the tires the actual pattern of vibration changes a bit but the speeds remain constant.

So if not the bearings then what?

 

Maybe a lost weight on the driveshaft or something, tires shouldn't change that though.

 

It's definitely balance somehow. Put 8 liquid ozs of RV antifreeze (non-toxic) in the tires to dynamic balance while driving. I used this on my Jeep with 35" Super Swamper tires that were never right. I could finally drive on the highway again after.

The antifreeze goes in easy with a funnel and small hose of you jack the tire and pull the valve stem.

 

I have never heard of placing any liquid in a tire.
These doe snot seem to make sense to me.
Has anyone else ever heard of this?

 

Well I wouldn't do it, but I have....LOL

Sounds to me like a bad U-Joint all the way around. When they go they like to vibrate at given speeds, but only in those speeds for the most part. One thing you might try is next time get into the speed and take you foot off the gas and see if it changes in any way. If so there you go.