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ss 12bolt rear end


Denny

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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.

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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. 

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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????

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BOP rear diffs are entirely different than the Chevy 12 bolts, and typically less desirable as well.

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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. 

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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.

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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. 

 

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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. 

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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?

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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

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