[dustyballs]

when i step on the gas or lay on the brakes the rear axle seems(sounds)(feels)to move.whats the cause?and how do i fix?any help would be great

 

[75F350]

This could be a simple case of axle wrap due to worn or fatigued leaf springs, or you could have a bad u-joint. You could also have worn spring eye, or shackle bushings, or even a driveshaft that requires some service. Might even be as simple as loose u-bolts.
The rear axle could have some play or loose tolerance due to many miles of use.
You are probably going to have to get under the truck and start inspecting some stuff. This problem could be many things.

 

[theramsey3]

when i step on the gas or lay on the brakes the rear axle seems(sounds)(feels)to move.whats the cause?and how do i fix?any help would be great

Are you sure it is the rear? I had the same problem on mine thought it was the rear it wound up being bad radius arm bushings. Just food for thought. If it isnt r/a bushings definitely check everything in the rear previously mentioned by 75F350 .