David DeCan

So I am getting all the pieces together to swap in the Chevy 12 bolt in place of the peg leg Olds "O" type.

Just for giggles I crawl under the car and check the length of the upper and lower rear control arms. The Chevy 12 bolt came with a set of used control arms.

So the lower control arms are exactly the same length as the ones installed in my 70 Cutlass with "O" type rear.

But the uppers are different. WHAT??? The 12 Chevy rear is out of a 68 Chevelle---I am told. We checked the numbers and it seems to be right. The uppers on the 70 Cutlass are around 12 1/2 inches approximately edge to edge.

The upper control arms that came with the Chvey 12 bolt are around 15 1/2 approximately. WHAT??

Any thoughts? I guess its possible he gave me the wrong uppers. I don't need them as I can use the uppers on the 70 Cutlass now. But I am curious--did a Chevelle come with different length upper control arms? Which ones should I use when installing the Chevy 12 bolt in the 70 Cutlass???

Thank you

Fun71

Back in the 80s I swapped a Chevy 12 bolt into my 70 Supreme and used the control arms for the original O-Type. I put the O-Type into a 70-ish El Camino during that swap - never even thought about swapping the control arms along with the diff.

svnt442

From what I know the control arms should be the same across the lines on the same platform.

TripDeuces

http://www.leverfamilysite.com/Rear_...Dimensions.htm

ELY442

That's what I did. I have a 12 Chevy rear from a 72 Chevelle and used my original control arms. I dont think the Chevelle came with different lengths of arms. Its still a A-Body car from 68-72.

monzaz

64-67 ARE LONGER THAN THE 68-72
THE UPPER CHASSIS CROSS MEMBER THE upper control arms mount to was moved back some to create a slight bit more room for passengers in the back seat...lol. VERY SLIGHT... they did it in the Impalas also they have short and long upper arms also.

Just use what you have on the 1970 olds you will be good.

Jim
J D

David DeCan

Thanks guys. That answers the different lengths of upper control arms. NOW I AM SCARED! Did the guy sell me a 64-67 12 bolt? We checked the numbers and it was a 68.

Can anyone tell me how to measure the 12 bolt width and the width of the 64-67 versus the 68-72?

It is very possible the guy gave me the wrong upper control arms. Which is fine as I can use the ones on the 70. I would just like to be sure before I drag the car and diff to the shop to swap and find I have the wrong rear.

Thank you. Thank you everyone who pitched in here. David

70cutty

64-67 12 bolt is only about an 1" shorter than 68-72. 64-72 measures 60", 68-72 61". Earlier 12 bolts are more desirable and more $$$$.

David DeCan

How do you measure? From where to where?

70cutty

Mesure it from backing plate to backing plate.
64-67 housing measures 53.25" from backing plate to backing plate and with the brake drums in place, the total width is 60.00".

1968-72 58.5" backing plate, with the brake drums in place the total width is 62.25/62.5"

oldsmobiledave

Are you sure? Is there a typo in your widths? How can the total width be 2.5" more on the late unit but the backing plate to backing plate width is 5.25" more?

David DeCan

I am getting more nervous after every post.

I measured. Trying to measure from the backing plate to backing plate is very difficult. There are 3/8 indents all over the backing plate.

Measuring from the face of the axle to face of the axle, outside to outside also very difficult with the backing plates in place. When I say face of the axle I mean--after removing the drum you are left with a flat surface with the wheel studs coming out of it. This would be a good measurement place if the backing plates were not in the way.

So I put the drums back on and carefully measured from the outside of the drum to outside of the drum. The tape kinked a bit as it went over the higher outer most rim of the drum, but it was minimal. 61 inches almost exactly.

So drum to drum 61 inches
Casting number:3917124NF Chevy 12 Bolt
Axle Tube Code: CW 0417B
Year Code: C68
Counted the ring and pinion gear teeth 43/13
Posi installed
What thinkest thou? Is it a 64-67 or a 68-72 (the one inch longer Chevy 12 bolt)

Is this going to swap over into my 70 Cutlass? You will remember the 70 has a peg leg 2.73 "O" type. Soon available for the hauling away .

Thank you for your efforts. Sorry for the redundancy of this post. If we cannot definitively ID from the above data, just going to pull it out and put them side by side.

David

David DeCan

Measured the Chevy 12 bolt, backing plate to backing plate--54.5" Also measured the 70 Cutlass O Type, backing plate to backing plate--54.5". We are done here. It's going in. Thanks all for patience and expertise. David

70cutty

You are correct, I don't know what exactly I was thinking about at the time. I'm working on my chevelle so numbers are getting crossed.

The correct measurement should be 64-67 54.25" and 68-72 55.25".

David I apologize if my post caused further confusion.

David DeCan

It has been pointed out that I measured between the plates. Oppps. The saga continues. I will take the drums off and hook the tape measure over the backing plates measure again. Soon....

David DeCan

Outside edge of the backing plates: 55 3/8. Confirmed 68 Chevelle 12 bolt, 3.31's. Thanks for everyone's input.

Kennybill

My Nephew's car had a 1968 or 1969 Impala 12 bolt housing. Kenny fron KTR set up the rear end, 4.10 full spool, upgraded yoke, Moser axles. He sold the car about 7 years ago.