What is the gear ratio for a GM rear end?

jpd37 · Feb 23, 2004

I have a 10 bolt GM rear end that I am trying to understand so I can determine how it is working with the rest of the drive train. I think it is an 8.2 or 8.5 inch gear. It has 41 teeth on the large gear. Can someone tell me what gear ratio this rear end is? I cannot count the pinion gear without breaking the rear end down. Don't want to go there. Any advice would be helpful.

OddRodder · Feb 23, 2004

Usually the ring gear will have something like 41-10 or 41-11 marked on the outer surface. If not, you could probably lighty mark a tooth of the pinion gear and count as you slowly turn the assembly!

jpd37 · Feb 23, 2004

Is it most common to have a 10 or 11 tooth pinion with a 41 tooth ring? I will do the rotation and count tonight to test that approach.

OddRodder · Feb 23, 2004

10 tooth would be 4.10 ratio and 11 would be 3.73 ratio. But there are some other ratios in the low 3.s that use the 41 tooth ring gear also!

jpd37 · Feb 23, 2004

OK. I'll check it tonight. I have the cover off so I will be able to be fairly certain what the ratio is.

M&M CUSTOM · Feb 23, 2004

The ring gear will have the ring AND pinion gear tooth counts stamped into it.

Axle Ratio Tooth Combination
2.56:1 41,16
2.73:1 41,15
3.07:1 43,14
3.08:1 40,13
3.08:1 37,12
3.31:1 43,13
3.36:1 37,11
3.42:1 41,12
3.55:1 39,11
3.73:1 41,11
4.10:1 41,10
4.11:1 37,9

poncho62 · Feb 23, 2004

If you can count the big gears teeth, you can see the small gear also.

What is the gear ratio for a GM rear end?

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