I sure could use some good advice/suggestions on rear suspension setup for this 3w I am building. Car will be early hemi/4 spd chopped highboy sitting on an original frame/stock crossmembers, 16" steelies with 7.50 and 4.50 bias. So far for the front it's reverse eye spring, 4" drop axle, hairpins. I have an original 39 rear spring, 36 rear radius rods which I could modify/use as a ladder bar. I am aware the straight 39 spring will require modifying the crossmember to work in a curve rear spring app. Longer pring perches would have to be sourced or made since the straight spring would sit back farther. So I am really interested in what folks are using in a traditional 33/34 highboy to bring up the rear especially regarding the spring and rear crossmember. My trunk pan is original and I really don't want to cut it up. Thanks.
Get a 36-40 rear crossmember and make it easy on yourself. You can use the 36 wishbones at their original width with the 39 spring, and adjust the fore-aft placement of the crossmember to fine tune the wheel fit in the wheelwell. Some guys like the tire scootched back a hair from stock on a highboy. You’ll need to do some mockups to see if you want to piecut the crossmember to lower it before you weld it in.
One way to put a 39 spring in a 34 rear crossmember is to shave about an eighth of an inch off the spring on either side. This only needs to be done in the center area of the spring - the part that fits up into the crossmember.
When I did my 34, I flattened a later crossmember, then, if you notice, they get narrower near the center. At exactly 16"s , (8 each side of center) the width matches to weld the 34 center into the 35&up member. I have a 40 rear end, and very little travel before it bottoms out on the bump stop pads, about 2 1/2" of travel, could use a bit more
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