Ring and pinion teeth count (1 Viewer)

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Can someone in the know help real quick? I bought a 9.5” ring and pinion set off CL that is brand new. It’s supposed to be 3.70 ratio and has 10 and 37 teeth on the pinion and ring, respectively. I have what I thought was a 4.10 diff in my garage and it has the exact same number of teeth on each. So, something’s not adding up here because I figured that different ratios should have different teeth count. Can someone please help? Maybe the diff in my garage is a 3.70 ratio??

Thanks guys!
Mike
 

Mtntopper

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Can someone in the know help real quick? I bought a 9.5” ring and pinion set off CL that is brand new. It’s supposed to be 3.70 ratio and has 10 and 37 teeth on the pinion and ring, respectively. I have what I thought was a 4.10 diff in my garage and it has the exact same number of teeth on each. So, something’s not adding up here because I figured that different ratios should have different teeth count. Can someone please help? Maybe the diff in my garage is a 3.70 ratio??

Thanks guys!
Mike
You would need to have a different number of teeth to vary the ratio. It sounds like the different sets of parts you are describing would have the same ratio.
 
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Thanks for the help. I’m new to diff work, but would like to add 3.70 to my fj55 build and I guess I had a spare 3.70 diff without knowing it. In all likelihood it came from an fj60, so now I need to see if my axles will work.
 

Steamer

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4.10 is 41teeth on the ring and 10 for the pinion.
37 divided by 10 = 3.70
41 divided by 10 = 4.10
 
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4.10 is 41teeth on the ring and 10 for the pinion.
37 divided by 10 = 3.70
41 divided by 10 = 4.10

Believe on the 40 and 60 series it's 9 on the pinion and 37 on the ring making it 4.11. 80 series on were 4.10. Just counting the ring gear on a diff you can't tell. Need to found both.

Meant count both not found. Fat fingers on the phone and phone having a mind of its and correcting a word to a new one. :bang:
 
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Steamer

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Believe on the 40 and 60 series it's 9 on the pinion and 37 on the ring making it 4.11. 80 series on were 4.10. Just counting the ring gear on a diff you can't tell. Need to found both.

Yes sir. You are correct.

R&P 4.11 b.jpg
 
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Steamer

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Interesting, clicked on the link and at the top is used 4.11 for $150. :meh:
I wonder if they make the 4.10 so they can use the same 10 toothed pinion as with the 3.70 set? Or, could the 10 vs 9 toothed pinion be a tad stronger being a bit larger diameter? I guess the 41 toothed ring gear would be a larger diameter also? Like you say. "Interesting".
 

Mtntopper

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Someone told me the that you get 4.10's when the teeth are layed out in inches, 4.11's are metric. I'm not smart enough to verify that with the math.
 

Steamer

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Someone told me the that you get 4.10's when the teeth are layed out in inches, 4.11's are metric. I'm not smart enough to verify that with the math.
You just devide the ring tooth number by the pinion tooth number and you get the ratio. It's that simple. There's no measurement in metric or sae. it's just a count of the teeth. 4.11 means 4.11 to 1 ratio. 3.70 means 3.70 to 1 ratio. And so on.
 

Mtntopper

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You just devide the ring tooth number by the pinion tooth number and you get the ratio. It's that simple. There's no measurement in metric or sae. it's just a count of the teeth. 4.11 means 4.11 to 1 ratio. 3.70 means 3.70 to 1 ratio. And so on.
I think I understand the ratio part. But was just pointing out that my understanding is that a 4.10 layes out perfect in inches and a 4.11 lays out in millimeters. That math I would just have to trust somebody else with.
 

Steamer

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But was just pointing out that my understanding is that a 4.10 layes out perfect in inches and a 4.11 lays out in millimeters. That math I would just have to trust somebody else with.
What are you measuring? There's nothing to measure. It's just a count of teeth.
 

Steamer

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The diameter of the ring gear basically stays the same.
So I guess if you go from 37 to 41 teeth on the ring gear, the teeth must get smaller to get'em all on there? And then the pinion teeth need to be smaller as well to match up? Hmm. Hadn't thought about that till just now.
 

pb4ugo

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Yep.
I think different manufacturers come up with different ways to get there. Toyota only offered stk 3.7 or 4.11, anything else is probably aftermarket for the 40 diff. I went to 4.88, I had to clearance the ring gear to get the center pin in, because it was thicker. The pinion was noticeably smaller too.
 

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