On the build sheet of my 1970 El Camino Custom it says that it originally came with a 2.73 posi rear axle (someone swapped it with a '69 3.08 non-posi). Is the 2.73 a 10 or 12 bolt? Would it say on the build sheet? Thanks!!

I believe the build sheet shows the axle code in one of the boxes. Post the code and many people here can tell you whether it was 10 or 12 bolt. My guess, however, is that it was a 10 bolt.

In the axle box (29) is says CH in it. Does anyone know where I can decode the letters in the boxes in the build sheet? I know what the options are but I want to know about the letters and numbers in the build sheet boxes.

Shawn,
A "CCH" is a 2.73:1 posi for 1970. Although the book I am looking at didn't designate whether it was a 12 bolt or not. A "CH" is a 1968-69 (maybe early '70?) 2.73:1 10 bolt posi. Maybe someone else can add more.

The engine your El Camino came with originally is significant as to which rear end came with it. Up to 350 2 barrel (250 horse for '70) came with 10 bolt; 350 4 barrel (300 horse in '70) came with a 12 bolt when a manual transmission was spec'd, and a 10 bolt with automatics.

I pulled a rearend out of a 70 Monte Carlo, about 9 years ago. It was the 2.73 posi as you describe and, it was a 12 bolt.

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Jungle Jim #105 Gold
70SS396 & 70 Malibu~ Cajun Country,Louisiana~
"Fight the good Fight every moment, every minute,every day. Make it worth the price you pay!"

I have a '70 Malibu originally with a 350 (4 barrel - 300hp) and a TH350. It had a 12 bolt 2.73 non-posi rear end.

Mine's got a 350/300HP engine w/4bbl rochester.