U-joints speed up and slow down as they rotate with angles applied to the input and output shafts, less angle, less speed variations. Get really crazy with the angles and speed variation is extreme. As long as both ends have equal angles, the speed variation is canceled out and vibrations will be at a minimum. With zero angle, the needle bearings in the caps do not rotate which leads to short life spans.
'57 GMC 102, Original 347 V8, HydraMatic, 3.08 rear gear, added A/C, disk front brakes, HEI, AFB carb, '98 Honda Black Currant paint. T-boned and totaled 10/12
'52 GMC 152 Stake Bed, Original 228, SM420, added A/C, HEI, disk front brakes, '67 Chev 3.55 rear gear. Gets used as a real truck.
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