I don't know much about setting up gears. But any mechanic shop or anyone that knows their stuff has always said if the job is done right it shouldn't make any noise and if it does not enough for you to complain about.

 

My richmond 3.90s have a slight whine to them around 70mph. Definately not loud though. I would have to guess you have a bad bearing.

 

Aftermarket may be a bit louder, but I would bet it's mostly due to an improper set-up. What did the pattern look like? Edit, never mind. I see you found the problem...

 

for some reason the new pinion bearing wasn't any good, so we reused the factory one and everything is works perfect now, we also found out that the magnet on the differential cover some how came off and got chewed up by the gears and we think this is what started the whole problem, and thanks for the help everyone!

 

dont know if its true or not but i've read or been told that it doesnt matter what brand you get, any 3.90 gear is going to have some whine to it??? just go to the 4.10!!

 

if you chewed up the pinion. . . did you use a new crush sleeve? Sounds like there wasn't enough pre-load.

Bearings are not packed on differentials. You pack wheel bearings only (trailers and older style front wheels). That's what the gear lube is for.

 

yea we used a new crush sleeve and it was a time getting it crushed, and there was about 5lbs of drag on pinion, the gears looked like they got wore just from the 2 days of him driving on them and they were brand new richmonds from the begining so we took them out and put his 3.42's back in so i think he is gona just sell them now to get some of his money back, im sure someone who has a racecar or something wont mind the whinning.

 

Sounds like your engagement is off. What did you set it at when shimming the carrier to the pinion?
Did you add the friction modifier agent? That may help some but won't fix true mechanical problems like improper engament.
What type of gear lube did you fillit with?

OOPS, should have read all the posts, looks like you found the issues.

 

did you break them in properly? Drive 30 min . . cool for 30 min . . . then keep the speed under 55 . . . change the oil after 500 miles?

 

Should be no whine if set up right ..I just installed YUKON 3.90's new carrier and pinion bearing set to GM specs ..no whine