U Joint Installation

The grease nipples should be located on the compression side of the ujoint. It they are on the tension side, the ujoint cross is weaker in application. Look at it like this: Pretend you have the car on a lift, and you are looking at the differential from the passenger's side rear wheel opening. Hold the ujoint up with the cups at 12, 3, 6, and 9. Imagine that cups 12 and 6 are connected to the differential yoke. These are the "drive cups" Cups 3 and 9 are connected to the halfshaft itself, these are the driven cups. In this position, the grease nipple should be at the 1:30 or 7:30 position. That puts it in compression. It should not be in the 4:30 or 10:30 position, or in tension.

This rule holds true for all ujoints, place the nipple after the drive cup, not before the drive cup. Probably overkill for a street driven car, but the correct way to do it. Also pack the joints manually as well as possible during assembly, don't just put them in then count on the grease nipple to give you full coverage.