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RIP (12/27/60-7/18/15)
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what does the term "true 12 bolt posi" mean?
thanks as always
Tk
ps if it turns out that my limited slip diff is afu, is it possible, perhaps with an arc welder to turn my LSD into a posi?
 

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Just a wild guess, here ---- but I'm taking a stab that the expression "true 12 bolt" is a reference to the larger/stronger GM axle that actually has 12 bolts securing the ring gear to the carrier inside. There is another rear axle, of the Oldsmobile persuasion, that has 12 bolts on the rear cover but internally only has 10 bolts on the ring gear - so in a manner of speaking it's not "a true 12 bolt" despite having a 12 bolt cover.

Posi, limited slip, safe-t-track, etc etc. all refer to an internal differential that's designed to power both rear wheels "most of the time" instead of just one, but you probably understood that already. "Posi-traction" is Chevy's brand name for limited slip, "Safe-T-Trac" is Pontiac's, "Sure Grip" is Chrysler, I think "Traction Lok" might be Ford's, but they all refer to the same thing - a limited slip rear.

So "posi" and "limited slip" are the same thing. The only thing you could do with a welder would be to weld the spider gears in the differential up solid, turning it into a "spool" --- a straight solid axle -- you wouldn't want that for the street.

Bear
 

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Anyone know if Pontiac used different cases for the safe-t-track units? Chevrolet changed the ring gear mount position depending on the gear ratio, so there were "2" series, "3" series and "4" series cases. I have one with 4.55 gears and the ring gear looks very thick, making me think that Pontiac just changed the thickness of the ring gear instead of making three different cases.
 

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what does the term "true 12 bolt posi" mean?
thanks as always
Tk
ps if it turns out that my limited slip diff is afu, is it possible, perhaps with an arc welder to turn my LSD into a posi?
TopKat, Don't use the welder method....you will have problems in turns (big time).....EITHER: rebuild your 10 bolt pontiac rear, with a nice EATON or AUBURN carrier, and the gear ratio of your choice. OR: You could "upgrade" to a GM 12 bolt rear, which is stronger but may also need a rebuild......IF you want to spend $3000, you can buy a rear end, complete, and ready to install from a company like MOSER.......:cheers Eric
 

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Anyone know if Pontiac used different cases for the safe-t-track units? Chevrolet changed the ring gear mount position depending on the gear ratio, so there were "2" series, "3" series and "4" series cases. I have one with 4.55 gears and the ring gear looks very thick, making me think that Pontiac just changed the thickness of the ring gear instead of making three different cases.
Your on the right track, but it's not the case that's different but the carrier, what the ring gear mounts to. The thicker the ring gear the smaller diameter the pinion gear too. Your existing carrier will probably be able to use a gear ratio as high as a 3:55 or maybe a 3:91. I would consult Richmond gear or maybe Randy's Ring and Pinion with what you have to see if they have a gear that will fit your carrier. :cheers
 

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Topkat, please, please, LISTEN to these guys. Stick an Eaton or Auburn unit and new bearings in yours and it'll outlast you. Talk to Rukee....he did his a few years back and it came out great. Knuckle: what the other guys said. The carrier is different between the 8.2 units. There is a 2 series that works with the 2.56-2.78 (really thin ring gear and massive pinion gear) a 3 series that works with 2.93--3.23, and a 4 series that works with 3.36 gears all the way to 4.33 gears (really thick ring gear and small pinion gear). Some folks shim out the ring gear to "make it work" when using the wrong gear set with the wrong carrier, but it's not a good solution. And, the carrier for thinner ring geared ratios would need to be machined to clear the ring gear...not really viable.
 

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Your on the right track, but it's not the case that's different but the carrier, what the ring gear mounts to. The thicker the ring gear the smaller diameter the pinion gear too. Your existing carrier will probably be able to use a gear ratio as high as a 3:55 or maybe a 3:91. I would consult Richmond gear or maybe Randy's Ring and Pinion with what you have to see if they have a gear that will fit your carrier. :cheers
Thanks for the information. In the old days, the GM parts listings reversed the popular terms, calling the part that the ring gear bolted to the case and the outside housing was called the carrier.

Either way, I want to put 3.55s on a posi unit that currently has 4.55s, if I can.
 

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Knuckle, I have never heard of 4.55's in an 8.2 10 bolt, but I haven't heard of everything. Since the 4 series carrier will handle 3.36, 3.55, 3.90, 4.11, and 4.33 gears, my bet is that it'll work with the 3.55's you want to put in.
 

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According to the MPC, GM parts listings never reversed the popular terms, calling the part that the ring gear bolted to the case and the outside housing was called the carrier.

Pontiac never had a factory 4.55 setup.
 

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4.55 seemed kinda steep to me, too. I got two rear ends in a deal, one with 3.55 open in a 1965 "case," one with 4.55 posi in a 1966 "case." So it seems as though the 3.55 will fit on the posi with out further issues. Just some parts juggling to put everything into the 1965 "case." We are having tire rubbing problems with the later diff in our 1965, I had never heard that the early (64-65) ones were narrower until I read it here. Thanks for the help!
 
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