drivetrain slack

[Firebirdformula99]

He guys so I've changed my motor and tranny mounts and the torque arm bushing to all polys and I changed the u joints and I still have slack its not when I take off from a stop but when I'm driving you can feel it kinda get slack if you let off and it slams when I give it gas I'm thinking its the rearends limited slip going bad? I don't know a lot about rearends I don't think its the tranny oh and I have a vibration around 50 miles an hour

[c5z28]

It might be you have to much back lash in the differential. If you have a dial indicator that you can mount to the ring gear you can see if it is out of spec, generally .005-.009" is within tolerance. As for the speed a quick check if you haven't done so already is to make sure it is strictly related to speed. Does it do it in every gear, does it still do it in neutral, and can you make it vibrate if you get the rpm in the right spot? If it is in fact strictly speed related you might have an out of balance wheel.
The limited slip would be more apparent in turns or by simple test of a burnout to see if it one legs or not

[Firebirdformula99]

ended up being the rear control arm bushing on the drivers side was shot

[pajeff02]

Sounds like a good excuse for an upgrade. Stock control arms are kind of flimsy.