See Figures 1, 2 and 3
The Astro and Safari van's rear driveshaft is of the conventional, open type. Located at either end of the driveshaft is a universal joint (U-joint), which allows the driveshaft to move up and down to match the motion of the front and rear axle. The main problem with the simple U-joint is that as the angle of the shaft increases past three to four degrees, the driven yoke rotates slower or faster than the drive yoke. This problem can be reduced by adding an additional U-joint or incorporating a constant velocity joint.
For most of the All Wheel Drive (AWD) vehicles covered by this guide, the front driveshaft uses two Constant Velocity (CV) joints to transfer the power from the transfer case to the front drive axle. The constant velocity joint is used because it allows the driveline angle to be adjusted according to the up and down movement of the vehicle without disturbing the power flow. For 1995-96 AWD vehicles the rear CV-joint (driveshaft-to-transfer case connection) was replaced with a double cardan joint, which serves a similar purpose, through the use of 2 spider and yoke assemblies.
As for the rear driveshaft, both ends are attached using U-joints, but the design is slightly different between the front and rear of the shaft itself. The rear driveshaft's front U-joint (injected nylon or internal snaprings) connects the driveshaft to a slip-jointed yoke. This yoke is internally splined and allows the driveshaft to move in and out on the transmission splines. On the production U-joints, nylon is injected through a small hole in the yoke during manufacture and flows along a circular groove between the U-joint and the yoke, creating a non-metallic snapring.
The rear driveshaft's rear U-joint is clamped to the rear axle pinion. The rear U-joint is secured in the yoke, using external snaprings (inside the yoke ears). It is attached to the rear axle pinion by use of bolted straps.
Bad U-joints, requiring replacement, will produce a clunking sound when the vehicle is put into gear and when the transmission shifts from gear-to-gear. This is due to worn needle bearings or scored trunnion end possibly caused by improper lubrication during assembly. U-joints require no periodic maintenance and therefore have no lubrication fittings.
A vibration damper is employed as part of the slip joint. This damper cannot be serviced separately from the slip joint; if either component goes bad, the two must be replaced as a unit.