As John just said "It's not the tube that's the problem". The rear axle in that truck is a poor one. My dad had a '39 1/2 ton that he had to rebuild the rear end three times(no, he's a good mechanic), and he drives things easy. When I got my '37 1/2 ton I tore out the entire drive train and replaced it with a '55-'59 1/2 ton drive train, stock 235, SM-420, open drive shaft, and HO-33 rear axle assembly. One of the nice things about this(other than being much better built than the original '37 stuff) is that it looks pretty much stock, so that unless you are pretty familiar with these old trucks, you wouldn't know it wasn't original. I also had the king pin bores in the front axle rebored and put the '55-'59 front hub/brake assemblies on it. Now all my brakes match also.
