Guest Posted November 19, 2000 Share Posted November 19, 2000 I have a twelve bolt rearend in my 70 Monte Carlo. I am only getting wheel spin on the right side. I have been told that I have a single wheel rearend. I would like to convert my rearend to a posi. I see posi units on eBay all the time. Can a single wheel rearend be converted to a posi with one of these posi units, or is there a lot of rebuilding that needs to be done? I don't know very much about this subject. Also, how many 12 bolts were posi and how many were single wheel? I welcome your advice and comments. Thanks. Steve http://home.swbell.net/pdqchevy/index_nn4.html Quote Link to comment Share on other sites More sharing options...
DaveC Posted November 19, 2000 Share Posted November 19, 2000 Steve, The answer is yes You just need to find someone who is capable of swapping out your "open-end" carrier for a "posi". It is not just a simple remove and replace. There are a number of tolerences that need to be just right to get the ring gear and pinion gear to mesh perfectly. Other wise the gears will waer prematurely. I've never seen any production figure on posi vs non-posi. ------------------ Dave C. 70 402 4spd Monte Carlo 72 350 Monte Carlo 69 427 Corvette roadster 86 Grand National 96 Impala SS Quote Link to comment Share on other sites More sharing options...
Andreas Posted November 19, 2000 Share Posted November 19, 2000 Here is what I did when converting from open end to a posi unit, I also stepped up to 3.73 gears. - Bought an Auburn Posi - Bought a rebuild kit with all bearings, etc. - Took out the rear axle (careful, its heavy) - Gutted the old internals - Brought the whole stuff to a Gear Shop (do not go to any Garage, if you want quality, go to a shop that does Gears only!), they installed the new parts correctly. - While I was at it, replaced control arm bushings, axle shafts, axle bearings, rear cover and stepped up to rear disk brakes - Put the "new" rear axle in, voila!, a 12-bolt Posi unit with all goodies!! Cost of all that: approx. $1500 incl. everything above, the posi alone was around $340. Would have been considerably more w/o my own work... Good Luck!! ------------------ 71 Monte 383 86 Monte LS ZZ4 http://go.to/Monte Member NMCOA, FGMCC "It ain't a car if it's not a Monte" Quote Link to comment Share on other sites More sharing options...
Guest Posted November 19, 2000 Share Posted November 19, 2000 Steve. To put a used GM posi in your 12 bolt first you have to determine your ratio. Remove the cover. On the edge of the large gear numbers are stamped. This indicates the number of teeth on both the pinion gear and crown gear. Divide small number into large. Ratio found. This determines which carrier you have. Example 2:73 is a 2 series 3:55 is a 3 series 4:11 is a 4 series. You need the proper series posi to fit. Then take it to a pro shop to install. I just went thru this with my 71. Had a 2:73 open orig. Swapped in 4:11 posi from 69 GTO. Too much gear for me. Went to 3:55. Happy now. Fred I have a twelve bolt rearend in my 70 Monte Carlo. I am only getting wheel spin on the right side. I have been told that I have a single wheel rearend. I would like to convert my rearend to a posi. I see posi units on eBay all the time. Can a single wheel rearend be converted to a posi with one of these posi units, or is there a lot of rebuilding that needs to be done? I don't know very much about this subject. Also, how many 12 bolts were posi and how many were single wheel? I welcome your advice and comments. Thanks. Steve http://home.swbell.net/pdqchevy/index_nn4.html Quote Link to comment Share on other sites More sharing options...
Guest Posted November 19, 2000 Share Posted November 19, 2000 Thanks to everyone who responded. I should have mentioned in my original message that I have a 3.73:1 rearend gear ratio. Do I understand this right that I would need a "3 serier" carrier for this ratio? Also, when I checked with the rear tires off the ground, the tires spun in opposite directions. Does this always mean a single wheel setup or could I possibly have a posi unit with worn parts? Quote Link to comment Share on other sites More sharing options...
Guest Posted November 20, 2000 Share Posted November 20, 2000 Steve.It means you already have a 3 series carrier. Now you need the suitable posi to go with it. Its possible you might have a posi with worn or sticky clutch packs. Take the cover off and look. Either way Id still take it to a pro. Fred. Quote Link to comment Share on other sites More sharing options...
Guest Posted February 23, 2001 Share Posted February 23, 2001 If it was available when I converted my open 3.31 to a posi 3.73, I would probably have gone with the Powertrax No-Slip traction system instead of a posi. They cost ~$420. You would be able to use your existing carrier and gears, and it can be installed without special tools. Musclecar Review just did a write up on it in the March 01 issue. Quote Link to comment Share on other sites More sharing options...
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