Will be changing rear ends.Currently have a drum 3.08 8.8. Considering 3.55 or 3.55 posi trac. Will I need new driveshaft, brake lines, master cylinder, proportioning valve? Posi trac certainly has discs brakes.

 

Not necessarily. Instead of changing the whole rear end, just regear what you have and put a factory LS or an Eaton Locker in.

You should be able to find a F150 8.8 3.55 axle with rear drums if you really want to change the whole thing.

 

Existing rear is vibrating harshly at times. Axle flange on one side wobbles slightly. Changed axle bearing but believe inner carrier bearing bad.