68 cutlass rear end

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68 cutlass rear end

Post by 68cutnut » Fri Jul 14, 2006 10:15 pm

hi dan leeth .here i have a 1968 cutlass. it has a 12 bolt type o housing code sa with a 10 bolt carrier and an open diff. and of course bolt in axles . is this a 8.2 or 8.5 ? what are my options on posi carriers for this rear? it now has a 2.78 gear which i dont mind as i am going to install a 3.50 low 4 speed .any info would be helpful thanks dan


12 bolt olds rear

Post by monzaz » Fri Jul 14, 2006 11:47 pm

Hi Dan, Welcome. The 12 bolt olds is a bit of a strange beast. I t is a good rear except for the expensive gears...lol. Ok on to the questions...

1st. the rear is like a 8.4 diameter ring gear...??? just the way it is. BUT you can use a 8.5 10 bolt 28 spline rear in it. The olds 28 spline are slightly different angle but it will work quite well. your 12 bolt has about 3 different carrier brakes meaning 2.41-2.56 is one carrier and 2.78 -3.23 is another and 3.42 and up is another and so on. I would say the 2 series will work for your 2.78 gears. Here is what you need to do remove the carrier put it on a bench and measure up to where the ring gear machined surface where the ring gear back mounts to. Get me that info and I will let you know which one is the right one for your 12 bolt olds to use with your gears you have right now. Or give me a day to tear through my archive boxs and see if I have not picthed them all. I might even have a posi for an olds 12 bolt on the shelf. Just ahve to double check the series it is. Hope this helps, Jim

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