The Stovebolt Site Forums The Shop Area Engine Shop 54-62 Open Driveline swap into closed drive housing????

I've been told that there is no need to buy expensive highway-gear swap kits for your closed drive 1954 and earlier Chevy/GMC truck because you can use an open drive pumpkin from a 55 and later GM. Could it be true? Do the open and closed pumpkins interchange?

Not quite correct. To clarify, the pumpkins swap only for the 3/4 ton trucks - which have always been open driveline.

No such luck for the closed driveline, you still need to go with the expensive swap kits.

-Boyo

I hate to disagree but I have installed the center section from 55-62 1/2 tons into 40-54 1/2 ton axle housings many times. They even use the same axle splines. The standard ratio is 3.9 which is not that much better then 4.11. There was a 3.7 option starting in 58 but it is rare. The auto ratio was 3.38 which Patricks reproduces. You will also need to remount the housing to the springs with solid pads.

Thank 68 Dave for mentioning that the rear centers do swap and that the rear axle housing will need pads on it to mount to the leaf-springs. The torque-tube rear ends get some of their rotational resistance strength from the torque-tube itself and did not need the spring pads.

You can put the later pumpkin in the torque tube housing with out changing the spring mounts. Just weld the mounts solid so they cant pivot and away you go.

Anybody know the rearend ratio of a 62 GMC suburban with 3-on-the-tree and V6-305?

Most likely it will be a 3:73, 3:90 or 4:11
Pull the rear cover and count the teeth or look for the numbers on the outer surface of the ring gear to be sure.

I was wondering if an easier(?) way to go open drive rear with the stock trans would be to find the front section of a 3/4T driveline and fit it in somehow. The stock 1/2T open driveshaft would have to be shortened, but the 3/4T set-up does go from closed to open (right around the back of the cab). Of course the rear axle will have to be hard-mounted to the springs. And there would be the problem of matching all the u-joints. Other threads say that isn't too difficult.