Re: Model 20 posi carriers

[TABunsey@xxxxxxx]

On September 30, 2004 j gray wrote:

> Are there different posi/twin grip carriers (center
> posi unit)for different gear ratios, or will any
> ring/pinion set work on any twingrip center section? I
> had HEARD that 2:73 ratio was all by itself???I need
> to know as soon as someone can respond...please. Reply
> directly as well as to the list "please". Thankyou for
> any help. Joe


                              RESPONSE:


THE FIRST SOURCE (AND BEST SOURCE) FOR AMC INFO IS THE AMC PARTS BOOKS. After all, AMC built the cars; they should know what they put in them!


Various aftermaarket vendors list their ring & pinion products as only being applicable for AMC model 20 carriers within a certain ratio range (typically 3.15, 3.31. 3.54, etc would use one carrier, and 2.87, 2.73 and 2.56 would use the others).

HOWEVER, AMC (in the AMC Parts books) only shows two center carriers:

"Open" carrier (non-posi) AMC #321 2051 for 2.87. 3.15, & up
    "            "        "           "      322 6978 for 2.56

"Locking" (Twin-Grip) carrier #812 0235 for 2.87, 3.15 & up
    There is no "Locking" carrier for the 2.56 ratios.

I am much more inclined to accept AMC's view than any aftermarket vendor. 

I suspect that the difference between carriers has to do with the diameter of the pinion gear ( the 2.56 ratio has 16 teeth) which causes the ring gear to be moved further away from the pinion gear centerline, thus necesitating the ring gear mounting flange to be moved away as well (thus requiring a different carrier housing). 

Best way to tell, just count teeth on ring gear. Here are the gear ratios and actual tooth counts:
These are AMC Passenger car ratios (Jeeps used same ratios PLUS some others not found in passenger cars)

Pinion gear/ring gear  =  Ratio

16:41  =      2.56
15:43  =      2.87
13:40  =      3.08
13:41  =      3.15
11:39  =      3.54
11:43  =      3.91

Bottom Line:  AMC only used ONE POSI CARRIER (AMC #812 0235) for ALL V8 posi applications.  This part number is good all the way back to 1968 and up through 1980. If AMC says that only one V8 posi carrier is used, then that is good enough for me.

HOWEVER, 2.56 gear ratios were NOT AVAILABLE in POSI (perhaps due to the ring gear movement discussed above)

When in doubt, check the AMC parts books FIRST!

Tom Bunsey

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