My mechanic just installed my GM motive 3:73 Gears with eaton posi differential, we put all new bearings in and the ratech install kit, my mechanic is really good, has done about 75-100 rearend installs.
We took the car out for a test drive and when we excellerate everything is fine no whining, when he lets of the gas and lets the car coast, The winning starts and is loud, My mechanic seemed very mad about it and has some possible ideas, BUT I am just curious what you guys think.
I need your help ASAP he is coming back over tomarrow moring

 

im no master tech but gear whine is usually caused by the backlash being set wrong. ask him what he set it to. i've always heard gm gears set between .05 and .08 but i've never run them myself so i guess this isnt really a lot of help. sorry maybe mindgame or shoebox or somebody will chime in and give you some good advice.

 

just so you know im sure you would get a lot more replys for this topic in the lt1 tech forum. a lot of guys have run into this problem before and fixed it. maybe try doing a search on it. good luck

 

The backlash may very well be wrong but it'll be closer to .006-.008 or something of that nature.
All gears are a bit noisy, some more than others due to materials and clearance I guess. The main thing to look for is the wear pattern. That will tell you more than anything else. Here's a link you should show your friend.

http://www.sixpackcuda.us/setuprear.html

-Mindgame