[Skidmark]

I bought a 12 bolt rearend from a good guy on py forum. He pulled it from a running Lemans we know it was not original to that car. He thought it was from a Chevelle.

The cast code 3959038 shows 1969 Chevelle maybe early 70.

The axel code was stumping me it is L S with E under those letters.

Born date -0422(letter missing)-

Has what appears to be factory gears 2:73

The Pontiac Manal list L S 2:73 for 1970 GTO/GP not sure if they mean 12 bolt or 10.2 doesn't say.

The E should be Eaton it is a posi unit.

One of the things I'm trying to figure out the 3959038 cast shows late 69 some docs say maybe early 70.

So I would think I have rearend out of a 1970 GTO, would date 0422 April 22 1970 still be considered early 70.

Date numbers 0422 I thought would be late production date for 1970

Thanks Chris

[1968GTO421]

I expect that 'ol Pinion head will be your go to guy for good info on your rear end. Best of luck.

[Scarebird]

a guy named skidmark worried about his rear end... user name checks out

['ol Pinion head]

The rear in question is a '69 Buick Skylark or Olds Cutlass rear mfg by McKinnon Industries in Canada. Many Oshawa built nothing special '69 Buick & Olds A-body's received this style rear & in the 2.73 ratio. Have pulled several of these two letter L coded McKinnon 12 bolts as cores.

This is a c-clip axle 12 bolt Chevy style rear originally assembled with a 3R pinion flange & it should have backing plates w/o the spotwelded on flanges. As coded & originally assembled it had a 2.73 (high ratio) 12 bolt Eaton posi carrier. Any sources listing the two letter L code 12 bolts as '70-72 GTO usage are mistaken. McKinnon also built some 12 bolts for Chevy A-body applications, those will have the common spotwelded flange style backing plates, small Chevy 1310 ujoint flange, or if a 278 casting & out of a higher horse 70 Chevelle, the 1330 style ujoint flange.

[dataway]

OPH ... I hope you write a book before too long.
The hobby needs this kind of info.

[Skidmark]

Originally Posted by Scarebird

a guy named skidmark worried about his rear end... user name checks out

Lol

[Skidmark]

Originally Posted by 'ol Pinion head

The rear in question is a '69 Buick Skylark or Olds Cutlass rear mfg by McKinnon Industries in Canada. Many Oshawa built nothing special '69 Buick & Olds A-body's received this style rear & in the 2.73 ratio. Have pulled several of these two letter L coded McKinnon 12 bolts as cores.

This is a c-clip axle 12 bolt Chevy style rear originally assembled with a 3R pinion flange & it should have backing plates w/o the spotwelded on flanges. As coded & originally assembled it had a 2.73 (high ratio) 12 bolt Eaton posi carrier. Any sources listing the two letter L code 12 bolts as '70-72 GTO usage are mistaken. McKinnon also built some 12 bolts for Chevy A-body applications, those will have the common spotwelded flange style backing plates, small Chevy 1310 ujoint flange, or if a 278 casting & out of a higher horse 70 Chevelle, the 1330 style ujoint flange.

Thanks for the excellent info.

[mgarblik]

o'l Pinion head: Tremendous wealth of knowledge on Rear ends and so much more. Really enjoy your posts. Seriously think about somehow storing some of your knowledge in some form. So much knowledge from our carb. ignition, and other experts on this forum.

[Skidmark]

So I originally thought I had a US built Chevrolet 12 bolt rear series 2 .Meaning that without using spacers the 2:73 ratio was the highest gear set I could use.

Now that OPH has explained that the evidence in fact proves I have a 1969 Canadian built GM 12 bolt 2:73 posi out of a Buick/olds built for Canadian use. I'm wondering if I'm still at my limit for high gears with the 2:73 in this rear?

Really wanted something in the low 3's posi.

Also the yoke is damaged on the case. The u joint measures 3 5/8 across which I think should be the 1330. Which I believe is what OPH said I should expect. Yoke appears to be early u bolts not strap. Any idea where to find a yoke? I haven't cleaned the one I got to see if numbers exist.

Thanks Chris

[Skidmark]

Here are a few pics.