I have always heard to use 3* on the rearend, but here's a part of a post from anothe forum I belong too........joe

This information was taken from a website that provides information to people like up, Drivetrain Specialists of Las Vegas - Las Vegas NV, 89102,

www.drivetrain.com/main.html
High angles combined with high RPM is the worst combination, resulting in reduced u-joint life. Too large and unequal u-joint angles can cause vibrations and contribute to u-joint, transmission and differential problems. The improper u-joint angles must be corrected.

Ideally, the operating angles on each end of the driveshaft should be equal to or within 1 degree of each other, have a 3 degree maximum operating angle and have at least 1/2 of a degree continuous operating angle.

RPM is the main factor though in determining maximum allowable operating angles. As a guide to maximum normal operating angles, refer to the following chart:

DRIVESHAFT RPM . . MAX. OPERATING ANGLE

5000 . . . . . . . . . . . . . . 3.25º

4500 . . . . . . . . . . . . . . 3.67º

4000 . . . . . . . . . . . . . . 4.25º

3500 . . . . . . . . . . . . . . 5.00º

3000 . . . . . . . . . . . . . . 5.83º

2500 . . . . . . . . . . . . . . 7.00º

2000 . . . . . . . . . . . . . . 8.67º

1500 . . . . . . . . . . . . . . 11.5º

When the transmission output shaft centerline and axle input shaft centerline are parallel, the u-joint operating angle permissible is length of driveshaft divided by five. Example: A short coupled driveshaft with a 15" length would be limited to 3 degrees maximum operating angle. A 30" shaft would be limited to 6 degrees.

When the transmission output shaft centerline and axle input shaft centerline intersect midway of the driveshaft, the joint angles are equal. However, due to the change to unequal joint angles during up and down axle movement, this is a more undesirable condition than parallel centerlines. In this case, the maximum u-joint operating angle is determined by dividing length of driveshaft by ten. Example: A 30" driveshaft with intersecting angles would have a 3 degree permissible operating angle.

I thought I'd give credit where credit is due. I remembered someone here posted something like this in the past. The important thing is to keep the difference between both angles as close to zero as possible. And now that the chart shows danger levels for increased joint angles, please keep rpms in mind when setting up to race.

Even with a resulting angle of zero, you can still exceed the allowable angles based on rpms. Like they say, you should have at least 1/2 degree working angle, even in a straight line shot, to keep the bearings rolling withing the trunion caps.