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Old 02-23-2004, 10:24 AM
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What is the gear ratio for a GM rear end?

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.

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Old 02-23-2004, 10:33 AM
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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!
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Old 02-23-2004, 10:52 AM
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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.
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Old 02-23-2004, 11:12 AM
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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!
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Old 02-23-2004, 11:18 AM
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OK. I'll check it tonight. I have the cover off so I will be able to be fairly certain what the ratio is.
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Old 02-23-2004, 12:40 PM
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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


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Old 02-23-2004, 12:52 PM
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If you can count the big gears teeth, you can see the small gear also.
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