Although aluminum driveshafts are strong and save weight in trucks, they are less forgiving than steel driveshafts to nicks and dings. Some manufacturers recommend replacing the shaft if scratches or dents in the tubing exceed 0.008 inch. This dimension also is the maximum for cracks in the welds between tubing and yokes, and for voids created in the tubing by a missing balance weight.
When replacing the universal-joint kit (journal cross and bearings), be certain to use a kit specifically designed for aluminum shafts. Incorrect kits can cause galvanic corrosion. Before replacing the kit, check the condition of the yoke cross holes for damage and raised metal. Minor sections of raised metal can be removed with emery cloth.
Source: Spicer Drivetrain Service, Dana