GM S-Series Pick-ups and SUV's 1994-1999 Repair Guide



On all models covered by this information, conventional, open type driveshafts are used. Located at either end of the driveshaft is a universal joint (U-joint), which allows the driveshaft to move up and down (within designed limits) in order to match the motion of the rear axle. The shaft is designed and built with yoke lugs (ears) in line with each other in order to produce the smoothest possible running shaft. Because some vehicles covered by this information utilize 2-pieces shafts and splined yokes, it may be possible to reinstall the shaft incorrectly or "out of the phase'' which would cause vibration. Many of these vehicles will utilize a keyed slip yoke to prevent this, but DO NOT risk improper installation. ALWAYS matchmark the shaft ends to the yokes before removal or installation.

Since the truck can be obtained in either 2WD or 4WD and in various cab/bed combinations (long and short beds, standard and extended cabs), four types of driveshafts may be employed. Some models will be equipped with a one-piece rear driveshaft, while others have a two-piece rear driveshaft which uses a center support bearing. Most 4WD vehicles are equipped with a front shaft which is a two piece telescopic type with internal splines.

On the front of the rear one or two-piece driveshafts, the U-joints connect 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 (one-piece) or the shaft splines (two-piece). On the rear of the one or two-piece driveshaft, the U-joint is clamped to the rear axle pinion. It is usually attached to the rear axle pinion by use of bolted straps.

For the front driveshaft on 4WD vehicles, the U-joints are secured to the transfer case and the front differential by the use of bolted straps. Located in the center of the driveshaft is a slip-joint, which allows the driveshaft to move in and out on its own splines.

On 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. Since plastic retaining rings must be sheared for removal and no snapring grooves are supplied, the production joints must be replaced as an assembly whenever they are removed from the shaft.

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 ends. U-joints require no periodic maintenance and therefore have no lubrication fittings.

On many 4WD vehicles, a grease fitting is supplied near the front (axle end) of the front driveshaft. A similar fitting is found near the slip yoke at the middle of the two-piece rear driveshaft assemblies. This fitting is to provide lubrication for the center slip joint. Chassis grease should be used at this fitting.