I'm really hating my 9 bolt right now. Finding parts was a nightmare, there's only one gear ratio available (3.73), etc.

Here's what I purchased:
- TA Performance girdle
- 3.73 (again, only ratio available. stock was 3.27)
- bearings/seals/etc
- shim kit
- new cones (not a new carrier, just cones. carriers are no longer available)
It has year old axle bearings/seals because the old seals were leaking.

For once I didn't do the work myself. I was uncomfortable doing gear work due to tolerances (backlash, etc) so I took it to the shop my mom goes to with the hatch full of new parts. I know both guys that work there and both are very good at what they do.

Everything got together, was shimmed correctly, etc. We took it down the road and it’s was 100% quiet until we hit about 45 mph by the speedo that’s now off because of the new ratio (will fix that after the rear is fine again). At that point a hum type sound developed. We said **** (and a few other things too ), took it back, and tore the whole thing apart again. Everything got reshimmed and tolerances were tightened up a little bit more. The noise is still there. At this point they told me to drive it for 500 miles and at that point we will change the oil to see how dirty it is, see if the noise has gotten better/worse, and check the gears for abnormal wear.

More on the noise: it’s only there at very low throttle (maintaining speed while cruising). Mid/full throttle makes the sound go away and coasting also makes the sound go away.

There was only one thing that raises my eyebrow about the install. When checking the gear pattern there was a recessed marking on each of the teeth. I mocked it up in this picture:



The markings/flaw/whatever were radical and present on every tooth in the same location.

Could this be the problem? Will it eventually wear flat? If so how long will this take? The markings weren't very deep at all.

from the pic, it looks like the pinion is riding pretty high on the ring gear.

It appears to be a pinion depth issue(I cant swear by it due to pic)

Grab a 87-89 manual for the 9 bolt rear and check out all pertinent specs and also pay close attention to the pinion/riung gear wear pattern chart.

Again, pic aint the best so I wont swear by it.

3:73 were never a factory gear here, so you may have an after market gearset(again I dont know). Aftermarket gear sets are almost never as quiet as factory gearsets because they dont have people complaining about noise

hope something here helps you

later
Jeremy

I probably should have specified. That's not my ring gear; it's just a picture I found online that I drew some red lines on to show what I was trying to describe.

I don't know if it's caused by the gear set (might be). It's just weird that the noise comes/goes with throttle.

Any idea where I could come by an 87-89 manual for the 9 bolt?

Did the shop check the tooth pattern after the backlash was set? It is probably in the center on the coast side (back) & high on the drive side (front). If so it was not shimmed correctly.

Yes, they did. It's possible that it might be off slightly still. I will swing by today and ask them about it.

Stopped by and Rick confirmed what I vaguely remembered (I was present/helping through the whole ordeal) - everything is nicely centered especially the pinion. If I remember correctly it’s a pretty big contact patch that looked good aside from the random flaw in the teeth I outlined in my first post. He said that he could shim for it to be quieter when I'm cruising but then it would be louder under load. He’s under the impression that it’s the gears and that they will lap in over time and the noise will get quieter/go away.

Also, the nose is present at light throttle and goes away at mid/full throttle. If it’s riding high on the ring gear would extra throttle make it ride lower and make the sound go away? Not knowing anything about it I would guess that extra throttle would make it ride even higher making the noise worse if that’s the case.

I'm just confusing myself at this point so I'm going to stop posting for a little while and let those who know more than me feed me some info

ah if everything is brand new it should not hum at all. i put used gears in that barely hum cuz we set them up right. also if you have heated the rear up more then three time which you probably have there is no point in even taking the gears out again because the metal has hardened and the pattern you have now is what you are stuck with. so no matter what you do now they will hum.

Everything was 100% new/sealed when purchased. The only stuff I bought online was the girdle and the clutches. The gears, rebuild kit, and shims were all purchased new from a reputable local shop.

Could it be the imperfection in the ring gear that’s causing this noise?

Ummm...I am no drivetrain expert however when they did my friends rear end in his mustang this summer, they forgot to put this special limited slip diff fluid in with the diff fluid. He said that the noise sounded like a hum. When he brought it back they noticed he was running a limited slip so they did a diff fluid change again and this time put the additive in. After that he was good to go.

That's a possibility. Right now I'm running crappy 80/90 with no addative. I figured that I would just add it when I change the fluid over to some synth 80/90 in a few weeks.

I believe the 9-bolt is not supposed to get additive. Being that it is a cone and not a disk LSD, the additive may cause excess slippage in the brake cones. Technically it is supposed to get 80W 90 MODIFIED GL-5. Since I don't know what the MODIFIED is about, just to be safe I went to GM with the original correct part# for the 9-bolt lubricant(#1050010) and they gave me today's equivilant. This link has a lot of useful info about rear axles used in GM vehicles, including the 9-bolt. In this article it is referred to as the "Borg-Warner model 78." Page 224 has info about lubricants, and the last thirty or so pages have diagrams.

http://fsunw3.ferris.edu/~millerm/SWB_a3_m06_Final.pdf