I upgraded my 9-bolt from a 2.77 to a 3.70 and I'm getting a whining noise under VERY light throttle, and when coasting. Ran a pattern on the gears and it seemed to be pretty much centered, maybe a little bit towards the toe of the gear, but not by much. New bearings were installed everywhere as well as a 3-series carrier I bought off of ebay. Car seems to be running fine with no clunks or grinding or anything. Any ideas? Perhaps the backlash is a little off? Is this a cause for concern? I talked to a guy who rebuilt a 9-bolt and he said he had trouble with whining too. Said he pulled the thing apart and checked everything, but it still whined.

 

Maybe this is why Randy's offers a 3.73:1 instead?

 

I was told that a 3.73 was not available for the Australian 9-bolt. 3.70 and 3.73 ratios are not that different either.

 

Ah, but they are. A 37-10 r&p has different tooth pitch than 41-11. Let's let BigGearHead weigh in on this.

 

So is it possible that the noise is caused by the gear pitch? I could care less if the diff is noisy. I just want to make sure I'm not imposing any damage on anything.

 

As far as I know all 9 bolt 3.70 gears make the same noise. Some places will tell you this before you place your order. All I can tell you is to get a louder exhaust or better sterio.

 

It whines because the gears are to tight. Your shim stack is wrong.