I have restored a 56 chevy and put in a 700r4 transmission and I have rebuilt/ replaced everything including front bushings, rear leaf spring bushings, shocks, put disk brakes on the front, put rack and pinion steering, installed front and rear sway bars, new u-joints and balanced driveshaft, new wheels and tires, etc and I still have a vibration at 55 mph and up. I can shift into neutral at highway speeds and I still have the vibration. Any ideas where else to look. This is driving me craze almost like the poison ivy I have right now.

oldchevy56,

Take a look at the rear U-joint to be sure it is centered in the pinion yoke.
Also with all the new and "up-graded" items in the powertrain double check the alignment of the output shaft of the transmission and the pinion angle of the rear end.

Good Luck

Pinion bearings .

Vince

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I will be looking at the rear end more closely as this is the one area that I have not rebuilt. I also am thinking about lowering the rear transmission 3/4in to provide a straight angle for the driveshaft.

oldchevy1956,

The output shaft of the transmission needs to be Parallel with the pinion of the rear end not in a straight line.

Scholman

I found that the transmission was too high. I lowered the transmission 2 inches and this became parallel with the rear end which still gave a slight slope of the driveshaft. I went for a test drive and the vibration was gone at all speeds even up to over 80 mph.