84 half ton

[red7d7]

I have an 84 half ton witha 12 bolt rear. When I hit 35mph I get a very distint wobbling sensation from the rear, It stays there until I hit around 40mph, then seems to go away. Above 50 I get the same feeling in the truck but not as bad. A while ago my son noticed that my right rear looked as though it was wobbling when I was driving down the road. I rotated tires and found that it stayed at the right rear no matter what tire and wheel was put there. Then I pulled the drum and axle shaft and replaced them both. Wobble in the right rear went away but still get the same feeling when driving the truck. I am thinking it might be an unbalanced drive shaft as the u-joints look and feel fine. Anybody have any thoughts as to what the problem may be?

 

[GMC1977]

any lift? maybe a wore out bearing? bent axle tube but not enough to put the shaft in a bind? the list can go on....

 

[chalet2506]

If the u-joints are older, go ahead and replace them - sometimes you can't tell by the look, feel. Also, if your driveshaft has some miles, try greasing the slip joint. They vibrate when they start wearing out. At least mine does, fresh grease every 1000 miles or so gets it by for now.

 

[chalet2506]

Might want to check the torque on the pinion nut holding the yoke on your 12 bolt, it could be coming loose.

 

[red7d7]

Forgot to mention that is is lifted. 4in springs in front and a set of blocks on the rear. 3in body lift as well. Bearings check out fine, tubes check out fine as well. Will check the pinon nut tomorrow morning as Ai have not thought of that yet. Thanks for the suggestions.