I am ready to set a hack body on the frame rails and I noticed that the driver side rail at the rear was about 3/4" lower than the other side.
I don't know how I missed that before?
I have a new rear spring and everything else is either new or rebuilt. I checked the front and it seems to be good. If I set a level across the frame right at the trans it is 1/4 " out and at the rear almost 3/4 ". Could it be the rear spring and should I flip it?
Check and see how centered the frame is on the rear spring, as well as double check that you have the leather pad that goes between the frame and the rear spring even left/right. When adding a Warford I had the rear end out and when I set it back down I noticed I was crooked - the leather pad had slipped to one side and it was a simple fix.
Since you have the body off now is a good time to measure the frame everywhere - there are other threads that say exactly how wide the distance between the rails should be everywhere, and you can measure the X, driver-side front to passenger-side rear, and opposite, and then make sure your rails are both straight. I'd check that the frame is sitting correctly on the rear spring before anything else though.
My problem was a loose spring center bolt. Allowed the top leaves to slip to one side. Easy to check without any disassembly.
The spring and pad should not be off-center if you have the proper square-headed spring center bolt nested into the square hole in the rear cross member. Possible problems may be a weak or cracked leaf in the spring pack or a tight spring shackle.
Measure and record the two measurements. Since the left side is lower loosen the left side U-bolt nuts about three turns. Then tighten the right hand bolts one turn. If the frame is coming up on the left side continue back and forth measuring both sides. snug the nuts and pin them. Don't bother using a torque wrench. With that leather pad in there it will drive you crazy. Back in the old days the length of the wrench handle determined how much force would be applied to a nut or bolt with out snapping or breaking it off. Since your spring is new, this should cure the problem.
One other thing--check your spring shackles. Their positions should be identical. If not, a rear radius rod adjustment may be called for at the front end of the drive shaft.---Len
Be sure that your SPRING SHACKLES are not too TIGHT !!! I have Ts come in that are tipped to one side because the shackels are way too tight and one side binds sticking down and he other side binds sticking up. Your shackels should not be much more than finger tight.