Hello. I am a noob when it comes to drive train related issues. I have a 4 speed 71 GS 350 that has a chevy 12 bolt in it. ID number on the housing starts with CW so it should be an open 3.31. Here is a pic of the internals if someone can confirm that or not. Cover is not off currently. My question is: Is there a way to make this a posi rear or should I swap it out with a buick posi rear? Thanks
Yes that is an open diff. Can't tell the gear ratio from looking at it, but you can count the teeth on the pinion gear and the ring gear and divide the ring gear # by the pinion gear # to see what the ratio is. Yes you can make that differential a posi all you have to do is get a different carrier to bolt into the case. Monzaz I believe his name is on the board probably has what you need to swap the posi unit in.
with the right posi carrier to swap in, youll be laying two black streaks in no time. Should be an easy swap too, so long as you intend to keep the gears you currently have. Check the backlash of the ring gear before removing the nonposi carrier. Then when you reassemble, shim the posi carrier to achieve that backlash. remember to preload the carrier bearings a little bit.
Spin the ring gear around wiping the outer diameter edge and see if the numbers are stamped there. IF they are not wipe the pinion top and get the number off that. IT appears to be all original. You have a 3 series carrier if it is 3.31 ratio 13 pinion teeth and 43 ring teeth. You can either install a complete posi unit 30140 GM (pictured with green springs)or aftermarket and reshim as stated in the previous post...OR you can install a power trax Richmond unit (picture 1 and 2 ) They are pretty easy and you do NOT need to remove anything but the axle shafts and spider gears. NO need to reset the ring backlash etc. The units do make some clicking noise in the turn as this is how the limited slip action works to release the axles in the turn link the clutches or cones would do in a factory posi unit. IF your just looking to play from light to light and tools around tow do some weekend grudge racing then the power trax is a pretty good choice with VERY little to mess with in the rear. Power trax also DOES NOT require any special fluid additive. The last picture is a power trax unit installed in a 3 series OPEN carrier just as you have pictured. PM if you want pricing on either units. Jim JD
Monzaz, Do you know if they make a Powertrax for the 10 Bolt 8.2 B & P 65-67 style open differentials? I tried looking on their site, but it is pretty... challenging.
Yes - they make a NO SLIP power trax. It is expensive and you have to use the large pinion cross shaft (.795 first 2 pictures) carrier NOT the (.733 last 2 pictures)cross shaft carrier unit. Pontiac large pinion cross shaft carrier will have 2 big open windows Buick and Olds will have the smaller .733 cross shaft one big window and the other is smaller around back. (middle 2 pictures compare the 2 open diffs) SO that is it. I will get you the Richmond number in a minute. Jim
Chris, Make sure you have the correct upper driver's side trailing arm for a 12 bolt....it is different than the BOP 10 bolt......if you are using the BOP arm...it will rub the case.....easy to tell the 12 bolt arm since it has a reinforcing plate spot welded to it.:beer
Hmm... unlikely that I will be able to come up with the parts cheap enough to make that worthwhile for me. Guess I will keep saving my pennies...
Guys thank you all for the input. Jim, that last one you have pictured....what does that one run for a price? I'm all for going with what is easier to get done.
George, Just took a peak under there. I don't see anything spot welded to it. I see plates welded to the lowers on the under side.
The lowers you describe are boxed for the rear sway bar. Here is a pic of the upper driver's side with spot welded metal plate......this is what you need or you will have the arm rub the case.
hey jim, i have ( what i am told) a 3:08 in my 72 gs. i wanted to make it posi. what would i have to do?
Just install any 3 series posi unit factory 410408 or 725 casting or aftermarket 28 spline unit Auburn, Eaton or true trac. I have a few true trac 28 spline units here if you need NEW technology for a good price 375.00 each. Regular hot rod shop price is 420.00 10.00 shipping to all 50 states. Jim
Please let me know the exact one...can you describe it better? Trying to help. Jim Power trax unit? That one? Jim 330 659 7117
Power trax also DOES NOT require any special fluid additive. The last picture is a power trax unit installed in a 3 series OPEN carrier just as you have pictured. Its the last pic you posted out of the four. thanks for the help
