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pont69lemans
Tribal Scout

USA
25 Posts

Posted - 30 Mar 2015 :  5:43:28 PM  Show Profile  Reply with Quote
I have a 1978 Trans Am with an 8.5 10 bolt posi in it with 2.56 gears the posi unit is in great shape I am wanting to put 3.42 gears in it but everything I see says the housing has to be 2.73 or above to make that work but I have been told they make a thicker ring gear to make up the difference does anyone know if that's true ? I have seen spacers to make it work but I'm not very crazy about using a spacer.

67drake
Sitting Duck

Azerbaijan
1501 Posts

Posted - 30 Mar 2015 :  6:23:36 PM  Show Profile  Reply with Quote
They do NOT make a thicker ring gear for the 8.5's (or 8.2's for that matter). This is an option if you have a 12 bolt.


71' GTO Original 400 M20 3.23 posi
13.95@102.1 MPH on street tires
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cortcomp
Coyote

USA
5338 Posts

Posted - 30 Mar 2015 :  6:32:09 PM  Show Profile  Visit cortcomp's Homepage  Reply with Quote
I wouldn't hesitate to use a spacer properly setup. I did have a thicker ring gear in my 8.5" O type 12/10 bolt, and they're hard to find parts for. No on makes them aftermarket?
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67drake
Sitting Duck

Azerbaijan
1501 Posts

Posted - 30 Mar 2015 :  6:44:56 PM  Show Profile  Reply with Quote
Not for an 8.5 or 8.2 10 bolt


71' GTO Original 400 M20 3.23 posi
13.95@102.1 MPH on street tires

Edited by - 67drake on 30 Mar 2015 6:45:28 PM
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cortcomp
Coyote

USA
5338 Posts

Posted - 30 Mar 2015 :  7:50:52 PM  Show Profile  Visit cortcomp's Homepage  Reply with Quote
Wow, that's crazy because they're common and the o type is hard to find parts for.
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67drake
Sitting Duck

Azerbaijan
1501 Posts

Posted - 30 Mar 2015 :  8:34:37 PM  Show Profile  Reply with Quote
I agree. I built an 8.5 that had it's original 2 series posi carrier,so I also thought about using the thicker ring gear. I talked to Jim at JD race and Randys ring and pinion and they confirmed that the thick ring gears are only made for the Chevy type 12 bolts.


71' GTO Original 400 M20 3.23 posi
13.95@102.1 MPH on street tires
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cortcomp
Coyote

USA
5338 Posts

Posted - 30 Mar 2015 :  8:59:01 PM  Show Profile  Visit cortcomp's Homepage  Reply with Quote
richmond made them for the O type 12 bolt (really an 8.5 10 bolt inside) but that's an odd bird, and they're usually on BO. I'm really surprised they don't make them for more common rears.
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