68 Cutlass 12 bolt rear end question
#1
68 Cutlass 12 bolt rear end question
My son has a 68 Cutlass with the 12 bolt cover, non-posi 273 gears. He wants posi with 355 or 373 gears...which they don't have much for these rear ends I've noticed. Whats the best choice, get a 68-72 Chevelle 12 bolt rearend, it should bolt right in, what about driveshaft length as he just had a $450 driveshaft made for his car.
#2
12 bolt chev differential will require drive line to be shortened to replace the Olds 12 bolt. I would look for a 71-72 8.5 10 bolt from a Cutlass. It will have the bolt in axles and uses corporate 8.5 10 bolt carrier and gears. I think you can use the same driveshaft you have with the 10 bolt not 100% sure.
#3
If you keep the O-Type, you are limited to 3.42, 3.90, and 4.10 for new ring and pinion gears. For a posi diff, either used GM O-Type (671 or 588 casting numbers) or new machined Ford 8.8 carriers are the only things I am aware of.
Swapping to a 71-72 corporate 8.5 inch 10 bolt opens up the range of gear ratios and posi choices.
Swapping to a 71-72 corporate 8.5 inch 10 bolt opens up the range of gear ratios and posi choices.
#4
no 2.73
My son has a 68 Cutlass with the 12 bolt cover, non-posi 273 gears. He wants posi with 355 or 373 gears...which they don't have much for these rear ends I've noticed. Whats the best choice, get a 68-72 Chevelle 12 bolt rearend, it should bolt right in, what about driveshaft length as he just had a $450 driveshaft made for his car.
You can get carriers & appropriate gears from several vendors who are board members. Rebuilding a rear end is not cheap. You have to pay to play.
#6
Fyi
If that is a 12 bolt Chevy 3.55 from a 71-72 455 HO car then you stole it.
#7
Agreed. My brother-in-law has the original 3.55 cone style posi behind his GTO and it has held up for years behind a stout engine, but he also has tires with almost no traction. It's one of those differentials with a split case and 10 bolts holding the halves together so it has some inherent weaknesses.
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