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  #11  
Old 04-20-2014, 02:35 PM
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I haven't dug through all of the responses above yet but I think I got it.

In my original post, I had bike drives on the brain and was thinking input- big gear, output- small gear. Duh. In a diff it's input-small pinion, output- big ring gear. What I think is happening is that the ring gear tooth count doesn't change for a given diff housing. The pinion has different available tooth counts to change the ratio. Therefor the pinion diameter changes and the ring gear diameter doesn't. the ring gear thickness changes to be able to mate with a smaller pinion. Low ratio diffs, (eg 5.26) have small pinions with undercut teeth which makes the weaker, and have thick ring gears with lots of meat to hold the bolts.
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  #12  
Old 04-20-2014, 03:15 PM
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Originally Posted by DaveInDenver View Post

What I wonder, then, is whether or not the ring gear is the same across a similar gear set. IOW is a 41-tooth ring the same on a 3.73 and 4.10 ratios with the pinion changing to match? I totally have no idea.

It could be the same number of teeth, but not the same actual ring gear. The pitch of the teeth would be different to allow them to mate with the pinion gear.
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  #13  
Old 04-20-2014, 10:12 PM
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Quote:
Originally Posted by Fishy View Post
It could be the same number of teeth, but not the same actual ring gear. The pitch of the teeth would be different to allow them to mate with the pinion gear.
And the thickness of the ring as well. As the gears get lower (numerically higher) the pinion head has less teeth and thus a smaller OD. The centerline of the pinion has zero adjustment and the carrier can only move a few mm max in many scenarios, thus the ring gear has to get thicker as the pinion gets smaller.
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  #14  
Old 04-21-2014, 07:59 PM
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Originally Posted by cruiseroutfit View Post
And the thickness of the ring as well. As the gears get lower (numerically higher) the pinion head has less teeth and thus a smaller OD. The centerline of the pinion has zero adjustment and the carrier can only move a few mm max in many scenarios, thus the ring gear has to get thicker as the pinion gets smaller.
Kurt beat me to it.

These two concepts:

(1) ONLY the number of teeth in the pinion and ring gear determines the ratio. I always get a chuckle when people speak of "3.73" on Land Cruisers. Doesn't exist. It is 3.70 due to 10 pinion teeth and 37 ring gear teeth. Likewise, 4.11 is 37 ring gear teeth and 9 pinion teeth (Technically 4.111111111111 etc.)

(2) The ring and pinion MUST BE precisely matched both to each other, and the 3rd member housing/bearings. This goes for all the relevant dimensions on both the ring and the pinion, including tooth profile.

We are having Carl Montoya from Nitro Gears sponsor Porcupine Rim on Friday at Cruise Moab. He's quite an expert in R&P gears and 3rd members as you might imagine. If you want to pick his brain at the event it would be a great opportunity. He has forgotten more about R&Ps than most of us ever knew to begin with.
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  #15  
Old 04-21-2014, 11:15 PM
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41/11 Jeff
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