Rather than spend a hundred bucks on the rebuild, i went ahead and purchased the Sniper EFI.

This was the end goal, just now had a reason to pull the trigger.

The 8 3/4" rear end is a XXXX657 center chunk. it is a 3.91 Posi unit, it came from my barracuda years ago. It now whines / howls going down the road. There is also a random odd vibration the can be heard and felt, and goes away once shifted into neutral.

Thinking bearings are worn on the center chunk, and this is causing the random vibration. I also have a 742 housing, sure grip but it has 3.23 gears. Should I just swap that and not worry about the 657? With the gear vendors i would like to keep the 3.91 though.

how do I check if the gears are worn out? Do i have to pull the pig and use a dial indicator?