Just a few hours ago I got a Eaton Posi and some 3.73's installed in my 89 RS. (The ring and pinion were used for only a summer in my friends car and are from motive gear and were installed by a professional) Anyways, after the guy installed mine (he has done several rear ends) he took it for a test drive and said it was good. I began to take it home and I believe i hear a very quiet hum from the rear end. I watched him do the whole procedere and the ring and pinion contact pattern was right on and as far as i know everything else went well. Should i be worried???

 

So you went from 2.73 to 3.73, right?

Well now your drive shaft is spinning as fast at 70 mph, as it used to be spinning at about 100. Which creates a GREAT DEAL more vibration, you can believe that.

It probably doesn't have anything to do with the gears themselves. Gears or bearings would more likely make a whining noise.

 

Well i'm not sure how to determine a hum or a wine, but the noise is there from about 35 to 60 and i imagine it would continue past that speed. It gets slightly louder with increased speed. This is a brand new posi unit as well, could it just be general noise from the whole new differential, (i mean not bad but just the general sound it makes??)

 

when i swapped from a 2:73 to my 3:73 i didnt set up the gears right and they hummed like a b$^ch, so i had to dig back into them and re-set things, did you get new bearings when you swapped parts?. also i hear that aftermarket gears are made of a harder stronger material than stock so they will not be as quiet

 

It has nothing to do with the material but aftermarket gears are not as quiet. Believe it or not there is a lot of technology that goes into gear cutting. Aftermarket companies just do not have the money for R&D that the OEM's do. The OEM GM gear will be quieter and likely be stronger. Don't believe the hype that aftermarket gears are louder because they are stronger. The OEM 4th gen f-car gear will be quieter and likely be stronger than any aftermarket gear.

 

a complete overhaul was done when the new (Used) gears were installed, all new pinion bearings and races, new carrier bearings and races and new axle bearings and axle seals, and i did put an anti slip additive for the eaton posi too. All new shims and ring gear bolts and everything, crush sleve, it's all new. It is just a quiet hum/ wine, very quiet. This whole procedure was done using a dial indicator and torque wrench. Call me crazy, but could it just be nautral gear noise???

 

did the guy just fill up the diff with gear oil or did he add the posi additive? my friend forgot to use the addative and his rear made a humming sound.

 

I've got a richmond 3.73 in my car, and its as quiet as my stock rear end was.
only problem I had in the begining was, when I 1st got the gear swap done. He didnt add enough posi additive. It would clunk when I turned the tires and went forward or backwards. It was fine going strait line. We drained some fluid out, added more posi fluid in, and I was good to go. I get no hummmm at all. If your getting a hummmm....he tightend up too much. You need to change that crush sleve and redo that part. You cant re use a crush sleve, once you gone to far.....you gone to far.

 

i recently got 3.73's (down from 3.08) and an eaton posi bolted into my car. the guys at the shop (circle track car builders) explained how 10 bolt rears have to be set perfect to keep such a low gear from whining. i had them set my rear up like they would one of their circle track cars and they SCREAM like a banchee. i'm gonna have the rear reset to quiet it down some 'cause it's nearly unbearable w/o an interior. the push is worth the noise tho!