The Stovebolt Site Forums The Shop Area Engine Shop Engine Alignment

The general rule of thumb is that the line of the engine crankshaft and the line of the rear axle input need to be parallel. That doesn't mean you need a straight line from crankshaft through axle; only that the angle at both U joints is roughly the same.

Easiest way is to get a magnetic angle measuring device (Harbor Freight, etc.) and make sure the clutch plate and axle input have the same angle.

This should be measured fully loaded: cab and engine installed (or weighted down with some bags of concrete, etc.) and wheels on the ground. I'd guess you'd put the engine in place, then shim the axle to fit.

If the angles are too different you will get vibrations - unlike CV (constant velocity) joints, U-joints spinning velocity changes as it spins faster and slower. If the angles are mismatched then the axle input is driven faster then slower even with a constant crankshaft speed. This obviously wears parts down quickly.

Now the tricky part...under acceleration the axle will rotate. Some folks put a few degrees of angle into the axle to compensate for acceleration...3 degrees springs to mind. This is probably more of a concern for the drag racers out there...

-Boyo