Rear Upper control arm differences

Weird, the things I learn here. I put a 12-bolt Chevy rear from a '70 Chevelle SS396 car in my '66 Le Mans after it grenaded, and had no issues. It had a sway bar that was added post-factory, as well, but the control arms had been beefed with pipe inside the arms to keep them from collapsing (not my doing, but it is what I would have done back in the day). Note that I did not use the upper control arms off the Chevelle. I wonder what it looked like after awhile? :eek2:

 

Well crap, I'm putting in a 12-bolt in place of the stock 10-bolt. Anybody got a good upper driver's side arm they want to get rid of?

 

You can just modify the stock 10-bolt arm to function like the 12-bolt one. They are the same arm, but with the notch cut out and the reinforcement added. Check the link farther up the page for some good photos.

 

54 Rich, The crusty arm looks like it has a wider flange to me. Put a dial calliper acros the middle of the arm at the flanges. I got 2.03" for the GS and
1.95" for the Skylark....Also another puzzzle. Canada built Skyalrks had 12 botl rear ends. No indication they used a beefed control arm.

 

Mine were stamped NL. 350 4-speed car, has the extra rear frame braces.

 

Here are two really god pictures showing the wider flange on my crusty old GS unit and the thinner flange on the skylark unit. I do not think this much difference could be manufacturing difference.

 

Well, did a couple of things. Listed in the parts book are two different part numbers with different bushing numbers. NK for standard, and NL for HD. Painted .75" high on the top face (According to the the book).

The parts book lists one part number for the arm and two different numbers for bushings.

So I took three sets and measured the fattest part of the flange, among other spots, including thickness. The flange seems to be the only variable.
The GS 400 HD with 4 Speed, was thicker than the Lark. However, the Cal GS was thicker than the GS. All 69 cars. The GS should be the NL set (4 speed, HD Suspension), busing is obviously different.

I think the difference is only in the bushing. Im using the best set I have, the GSs are junk. I think the picture I posted was the camera angle that made them look so different.
:beer

 

70-72 GS had code PX. Some codes were inked stamped some had paper tag and some stamped in Steel. Maybe the wide lip was a plant mold type deal. Funny however that the heavy duty Buick I have and Heavy duty Olds on friends car are both wider than the standard NK I have.