Denny Posted July 17, 2022 Share Posted July 17, 2022 is there a differance in the 12bolts put in the 70 ss from other 12 bolts? Quote Link to comment Share on other sites More sharing options...
714024SPEED Posted July 17, 2022 Share Posted July 17, 2022 There is no difference in an SS 12 bolt and others housing wise. There were options on gear ratios,open or posi. The standard gear ratio in 70 was a 2.56 open rear. A posi traction was an option in 70 and 71. 2 Quote Link to comment Share on other sites More sharing options...
Dtret Posted July 17, 2022 Share Posted July 17, 2022 The short answer is yes. But Kevin just beat me with the reasons, less typing for me. Lol. Don’t forget the BOP 12 bolts. 2 Quote Link to comment Share on other sites More sharing options...
Denny Posted July 18, 2022 Author Share Posted July 18, 2022 whats bop mean? Quote Link to comment Share on other sites More sharing options...
Dtret Posted July 18, 2022 Share Posted July 18, 2022 5 minutes ago, Denny said: whats bop mean? Buick Oldsmobile Pontiac There’s something different with them, I’m not exactly sure what but I was told it was in the mounting???? 1 Quote Link to comment Share on other sites More sharing options...
jft69z Posted July 18, 2022 Share Posted July 18, 2022 BOP rear diffs are entirely different than the Chevy 12 bolts, and typically less desirable as well. 1 Quote Link to comment Share on other sites More sharing options...
Dtret Posted July 18, 2022 Share Posted July 18, 2022 There you go Joe knew. So be careful when someone says they have a gm 12 bolt for sale. What you buy may not fit your car. 2 Quote Link to comment Share on other sites More sharing options...
jft69z Posted July 18, 2022 Share Posted July 18, 2022 7 minutes ago, Dtret said: So be careful when someone says they have a gm 12 bolt for sale. What you buy may not fit your car. Some are deceptive too. One of the Olds diffs has 12 bolts on the rear cover, but only 10 bolts on the actual ring gear inside the case. It'll have a smooth rear cover, unlike the Chevy cover with the rib stamped on it to direct oil to the bearings. 2 Quote Link to comment Share on other sites More sharing options...
Denny Posted July 18, 2022 Author Share Posted July 18, 2022 thanks for all the info! very helpfull Quote Link to comment Share on other sites More sharing options...
Scott S. Posted July 18, 2022 Share Posted July 18, 2022 17 hours ago, Dtret said: Buick Oldsmobile Pontiac There’s something different with them, I’m not exactly sure what but I was told it was in the mounting???? U-joints and mounting points were the biggest differences. Although Moog has almost anything to solve that problem. Monte Carlos at the end of year runs were most likely to get these parts, as Chevelles were the priority on the assembly line. And when there weren't enough parts to go around, G.M. brought in what hadn't been used for LeMans, Cutlass, and Skylark models. Quote Link to comment Share on other sites More sharing options...
Scott S. Posted July 18, 2022 Share Posted July 18, 2022 9 minutes ago, Scott S. said: U-joints and mounting points were the biggest differences. Although Moog has almost anything to solve that problem. Monte Carlos at the end of year runs were most likely to get these parts, as Chevelles were the priority on the assembly line. And when there weren't enough parts to go around, G.M. brought in what hadn't been used for LeMans, Cutlass, and Skylark models. Something else to make note of..... Not sure if anyone else found this, but when I went from the 8.2" 10 bolt to a 12 bolt, the upper control arms spread due to the larger differential case. Because of this, the exhaust had to be "shifted" to clear the arms. Something I didn't notice until the car was back on the ground. 😒 P.S..... the B.O.P. internals are all different as well. Quote Link to comment Share on other sites More sharing options...
Denny Posted July 20, 2022 Author Share Posted July 20, 2022 the guy rebuilding my orig. 12 bolt from my 70 monte told me my bearing surfaces were shot ,so i pulled axles out of a 72 monte parts car i have but after noticed the rear cover is smooth also 72 axles were heldin with 4 flange bolts by the backingplate thought all 12 bolts were held in by c clips? Quote Link to comment Share on other sites More sharing options...
MC1of80 Posted July 20, 2022 Share Posted July 20, 2022 The smooth cover and bolt in axles are of the BOP variety rear ends. Chevy rears are c-clip. The Olds style rear in the 72 is not factory. Most likely swapped sometime in it's life 1 Quote Link to comment Share on other sites More sharing options...
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