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12 bolt diff..

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03-25-2005 05:40:14

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ok so i've got a 12 bolt gm rear and im trying to buy a ring and pinion gear. everyone ask's me is it 3" or 4" carrier. what do i measure to determin this... or is there another way to tell with out dissassembly? thanks in advace for any input that you guys have...

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03-27-2005 01:39:26

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 Re: 12 bolt diff.. in reply to 68c10lwb, 03-25-2005 05:40:14  
They want to know if it is a 3 or 4 series carrier.

if you have 3.07- 3.73 gears you need a 3 series carrier. If you have 3.73 or higher gears you need a 4 series carrier.

The difference is in the offset of the carrier putting the ring gear farther from the pinion center so the pinion can be a larger diameter and have more teeth allowing the higher gear ratios.

Sometimes ther are aftermarket gears that can put the 4 series gears on the 3 series carrier. 3 series carriers are more common and cheaper.

To determine the gear ratio there are numbers on the ring gear like 41-10 the 41 is the ring teeth count the 10 is the pinion teeth count. This would be a 4.10. divide the larger # by the smaller # to get the ratio.

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03-27-2005 11:48:36

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 Re: Re: 12 bolt diff.. in reply to DJ, 03-27-2005 01:39:26  
thanks for the info guys. i am ordering a 3.73 gear cause i currently have a 3.07 and trying for a great street strip gear. mostly street with the occasoinal stop lighter and weekend strip runs. again thanks for the info now i know which one to order...

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Kent of SW MO

03-25-2005 06:27:56

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 Re: 12 bolt diff.. in reply to 68c10lwb, 03-25-2005 05:40:14  
It is not 3" or 4" carriers. It has to do with the ratio the carrier can be used on. A 3 carrier is needed for ratios any where in the 3 range like a 3.73 or a 3.23. A 4 carrier is for like a 4.11. Some companys bulid a 4.11 gear for use on a 3 carrier. If you get the wrong set-up you either wil not be able to get the ring gear and carrier in the axle housing or if you can get it in you will not be able to set the backlash.


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