CLUNK! From rear end when shifting from reverse into drive

[BT5150]

Lately, whenever I shift into drive from reverse after backing out of my driveway, I hear a fairly loud clunk coming from what sounds like the rear end. Its just this one clunk and no repetitive noises after that. Any ideas? Its a 1990 AWD Astro.

[RECox286]

Put jack stands under the rear axle, and shift the tranny into anything other than PARK. Get under the truck, one hand on the drive shaft,

and one hand on the yolk. Twist in opposite directions. If you see any movement of the U-Joint itself while doing this, then it's time

for a new set of U-Joints. If you don't see any U-Joint movement, then load the pinion gear (the input shaft of the differential)

to one direction, when you see movement of the tires, then turn the pinion in the opposite direction, until you see the tire move.

In essence, you are trying to determine how much slop there is in the gear mesh. I would suspect you will find that the problem

is bad U-Joints.

Good Hunting

Uncle Bob