ok,i just put new axles and rear cover on my gm 12 bolt rear.now it make a noise when in gear.i used lucas 80/90 weight oil with some limited slip lube.i fill till it started to run out.car drives good.what did i do wrong?

 

What kinda noise is it making whinning?Did you change the gear set?or just the axles.Any vibration with it?
My 8 1/2 10 bolt makes a slight whine at 30-45mph with the gear set i have but the wear pattern an backlash are good.

 

just a slight whine.no vibration.it has stock gears in it.

 

...What happen to the old ones? That you had to replace it? did you get them from the boneyard? What condition were they in?? did you check them out fully before you instahled it? Were they comfortably seated in the pig?...Also what condition were the bearings? With so many variables and in complete info..its hard to say....You do realize...when an axle fails..it also effects the gears inside the pig! You Just may have done more damage to the complete rearend than you realized!( maybe theres debri in the diff!)....Is it a POSI rearend?....Being a 1972 model.. If im not mistaken..Its suppose to have straight 90 weight gear lube...not 80/90...If its a posi...the gear lube is different! Than your standard rear end lube......IMO...If everything was normal...and you did a complete cleaning of the diff...before instahling the rear axles and all the splines were correct on the axles and the outer gears (in the diff) were un damaged...Then it should be noise free if done cleanly and correctly...

 

My vote goes to debris in old fluid that did damage to bearings/races and now with new fluid it is making more noise.

 

your vote wins.i had to replace the bearings.runs great now.i broke the driver side axle with my mighty 295hp motor in the first place.

 

I'm curious/confused. Which bearings (axle/carrier/pinion)?