www.jdrace.com

Posted: **Sun Oct 29, 2023 12:47 pm**

Have a 1981 2nd gen Firebird with a corporate 8.5" 10 bolt rear 3.42 ratio.

I need to change out the original 105K mile R&P due to some loud gear whine at 45 mph+ when coating. I am going to "assume" it's a worn r&p causing this because I had all new bearings installed in this diff a year ago due to a lot of bearing rumble. I don't know if the whine was there before the bearing swap because it was kinda loud with all the bearing noise.............it could have been idk.

The bearings were changed out by a driveline shop and they did check the pattern afterwards and said it was ok but it whines when coasting when going over 40 mph.

I know a typical set of aftermarket gears would be ok for this but this car is a keeper and I would be willing to pay more for GM gears.
Can I use a gear set from a newer GM 8.5" rear end such as a 2001 chevy 1500 pickup truck? Will those fit an older 1981 car rear end?

GM lists a gear set PN 23114031 for a 2001 silverado

Is it the same? Pinion diameter, ring gear bolt size, etc?

Posted: **Mon Oct 30, 2023 2:18 pm**

Ok, Well It sounds like maybe something was not installed totally correct if the driveline shop said the pattern looked good and they drove it and it was quit...???
Anyway... Yes all 8.5 gears are 8.5 gears truck car SUV etc.
1971 -2023 even.
BUT be careful with new 8.6 gears they have some 2 cut gears and the backlash is MUCH tighter then the 5 cut 8.5/8.6 gear.
Good luck and yes if you want quit gears GM would be the best. EVEN USED .

Posted: **Mon Oct 30, 2023 5:20 pm**

monzaz wrote: ↑Mon Oct 30, 2023 2:18 pm Ok, Well It sounds like maybe something was not installed totally correct if the driveline shop said the pattern looked good and they drove it and it was quit...???

They never drove it. I dropped the rear end off and had them change the bearings then I reinstalled it in the car. I saw it had gear marking paint on it so they did do a pattern check. They never contacted me and said the ring & pinion didn't look and should be replaced.
It whined after I reinstalled the diff and drove it myself. I don't know if it had this coast whine @ 45-50 before the bearing swap as the bad bearing noise was too loud.
Can the ring and pinion just be worn out? They do have 105K miles on them.......or maybe because it ran for a long time with bad pinion bearings it caused an issue with the r&P?
I'm just curious what may be causing it.

Here is the ring gear from a GM OEM NOS 8.50 & 8.625 Rear Axle Ring & Pinion Gear Kit 3:42 Ratio (26038865) I am thinking of buying on ebay. Is this a 2 cut or 5 gear? Can you tell by the pic?
I want to stay with a 5 cut gear set but I am not sure which are which.

Posted: **Mon Oct 30, 2023 5:56 pm**

Where is the pinion? Need to see it.

Posted: **Mon Oct 30, 2023 6:38 pm**

Posted: **Tue Oct 31, 2023 9:31 pm**

appears to be a standard 5 cut gear. Jim

Posted: **Wed Nov 01, 2023 12:26 pm**

Is that surface rust a concern? I assume some scotchbrite will remove it as long as there isn't any pitting?

Posted: **Mon Nov 06, 2023 10:12 am**

nothing I can see on that gear has any issues. Yes you can do a scotch brite pad wire wheel etc to remove that surface stuff.
Jim

www.jdrace.com

GM ring & pinion gear set

GM ring & pinion gear set

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