Drive line angles?

[jayem]

What are the optimum angles for the front and back of the drive line. I have been told that the front must not exceed 8 degrees, the back must not exceed 8 degrees. Also that the front and back must be within 2 degrees of each other. Is this correct? Jay

[mickmate]

U-joints need a couple of degrees to work the bearings. Some theories are the needle roller should make at least one turn. You don't want to set up harmonic vibrations from being too straight either. They like a 2 or 3 degree angle, 8 sounds a little much if you can minimise it. You definetely want them alot closer than 2 degrees to each other, they need to be exactly the same (unless you're drag racing). A digital angle guage will give you within a tenth of a degree or so. They cost about $140 which is what you need if you're that far into it. They're very handy for camber checks etc.

[speed220mph]

It's true that U-joints need to be run at a minimum angle just to keep the needles working in their cups. Otherwise the needles will Brinell its cups by sitting in one location and beating a groove into its races. As for what static degree this should be, maybe 1-1/2 degrees at each joint, but in opposite directions so the angular velocity changes of the front joint is cancelled out by the second joint.

If you've got a Cobra with a live axle, the driveshaft is short and angles change a lot for each inch of wheel travel. But whatever the angle change, front and rear angle changes should be nearly the same for the reason given above to prevent non-constant velocities at the output end of the driveshaft.