Rear end noise when brakes applied

[85SERRIACLASSIC]

alright i have no idea what this could be. I have done a search and came up with nothing. I have a 99 Z 71, when i brake i have a vibration (whole truck shakes) and clunking noise comming from the rear end. Pulled the tires off yesterday and found that you can turn the axles 360 and sometimes more freely and the drive shaft does not spin when in neutral. then the axles seem to catch and turn the drive shaft. Only notice when using brakes. Any ideas on what may be happening

[DavesRide]

Look at the inside surfaces of the rear rotors. They have a bad tendacy to rust and sluff off causing lots of lateral runout. Don't bother having them machined, just replace them if they are looking crusty. The rear diff sounds normal for a limited slip centrifical lock style.

[85SERRIACLASSIC]

That is what we originally thought too but we checked the rotors and they looked fine. Sound seems to originate from the center of the rear diff. Its sounds like a loud clunk. Even does it by turning by hand. We pulled the cover off and checked the gears and they looked good, no metal in the grease when we drained it. All teeth looked to be in really good shape.

Is it possible that the carrier is worn out. Truck has almost 150,000 miles on it. Had 135,000 when i bought it. dont know much about it other than that. sounds like something is binding up and then letting go. You can feel it bounce around when you get on the brakes, in the steering wheel as well. I dont want to keep dumping alot into it because i know that i wont get it back when i trade or sell. Thought about a Detroit E-Z Locker or Powertrax No-Slip System. dont know if that would fix or not.

[centsless]

If you are getting a pulsation when the brakes are applied, then the rear rotors are warped. This will cause the rear to feel loose then tight when rotating it by hand. You can install the lug nuts on the rotor and then use a dial indicator to check it, or just prop something up against the rotor surface then spin it to see if it has runout. If so, replace the rotors to cure the problem. Also replace the pads, even if they are good. Do not use old pads on new rotors.

[85SERRIACLASSIC]

Thanks for the response but i have already tried all of those things. I really dont think that its the brakes. Bought new rotors, pads, the hole works and still have same problem. Its not really a pulsation, but a hard shake and a loud clunking sound, shakes the whole truck. Kind of like the sound that you would hear by hitting an anvil with a sledge hammer. Sound seems to happen at the same spot in the rotation. feel slight vibration during take off and cruising speed. Its really driving me nuts trying to figure this out.I may just trade it off, its really getting to be a PITA.