GM Full-Size Trucks 1970-1979 Repair Guide

Rear Driveshaft

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REMOVAL & INSTALLATION



See Figures 1, 2, 3, 4, 5 and 6



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Fig. Fig. 1: Rear driveshaft with the U-bolt attachment



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Fig. Fig. 2: Rear driveshaft with the strap attachment



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Fig. Fig. 3: Alignment key - 1977-79 K models with 2 piece driveshafts only



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Fig. Fig. 4: U-joint alignment - 1977-79 K models with 2 piece driveshafts



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Fig. Fig. 5: U-joint alignment - 1971-72 C/K trucks and 1974 K models



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Fig. Fig. 6: U-joint alignment - 1975-76 C models with 16 splines

A thump in the rear driveshaft sometimes occurs when releasing the brakes after braking to a stop, especially on a downgrade. This is most common with automatic transmission. It is often caused by the driveshaft splines binding and can be cured by removing the driveshaft, inspecting the splines for rough edges, and carefully lubricating. A similar thump may be caused by the clutch plates in Positraction limited slip rear axles binding. If this isn't caused by wear, it can be cured by draining and refilling the rear axle with the special lubricant and adding Positraction additive, both of which are available from dealers.

1973 C-10 and C-1500 long wheelbase pick-ups equipped with either the Turbo Hydra-Matic 350 or 400 transmission may suffer from a driveline shudder during acceleration. This can be corrected by installing a spacer between the driveshaft center bearing support and the hanger to which it is attached. The spacer should measure 7 3 / 4 in. long and 1 1 / 4 in. wide, and be 1 / 2 in. thick. Two 1 / 2 in. diameter holes should be drilled at either end, centered 9 / 16 in. from the end in the long dimension and 5 / 8 in. on the short dimension. This places the centers of the holes 5 / 8 in. apart. Install the spacer between the center bearing support and the hanger using bolts 1 / 2 in. longer than the ones removed.

  1. Raise and safely support the vehicle with jackstands.
  2.  
  3. Scribe alignment marks on the driveshaft and flange of the rear axle, and transfer case or transmission. If the truck is equipped with a two piece driveshaft, be certain to also scribe marks at the center joint near the splined connection. When reinstalling driveshafts, it is necessary to place the shafts in the same position from which they were removed. Failure to reinstall the driveshaft properly will cause driveline vibrations and reduced component life.
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  5. Disconnect the rear universal joint by removing U-bolts or straps. Tape the bearings into place to avoid losing them.
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  7. If there are U-bolts or straps at the front end of the shaft, remove them. Tape the bearings into place. For trucks with two piece shafts, remove the bolts retaining the bearing support to the frame crossmember. Compress the shaft slightly and remove it.
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  9. If there are no fasteners at the front end of the transmission, there will only be a splined fitting. Slide the shaft forward slightly to disengage the axle flange, lower the rear end of the shaft, then pull it back out of the transmission. Most two wheel drive trucks are of this type. For trucks with two piece driveshafts, remove the bolts retaining the bearing support to the frame crossmember.
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To install:
  1. Installation is the reverse of the removal procedure.
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  3. It may be tricky to get the scribed alignment marks to match up on trucks with two piece driveshafts. For those models only, the following instructions may be of some help. First, slide the grease cap and gasket onto the rear splines.

    1977-79 K models with 16 splines, after installing the front shaft to the transmission and bolting the support to the crossmember, arrange the front trunnion vertically and the second trunnion horizontally.
     
    1973 C and K models, 1974 C models, 1975 and later models with 32 splines have an alignment key. The driveshaft cannot be replaced incorrectly. Simply match up the key with the keyway.
     
    1975-76 K models with 16 splines, align the trunnions vertically. The shafts should not be rotated before installing the rear shaft to the front shaft.
     
    1975-76 C models with 16 splines, after installing the front shaft to the transmission or transfer case, must align the trunnions vertically, then the rear shaft must be rotated four splines (90 degrees) to the left (driver's) side before installing the rear shaft to the front shaft.
     
    1971-72 C and K models and 1974 K models, after installing the front shaft to the transmission or transfer case and bolting the support to the crossmember, rotate all the U-joints so the trunnions are vertical, then rotate the rear shaft four splines towards the left (driver's) side of the truck before installing the rear shaft to the front shaft.
     

  4.  
  5. On two wheel drive automatic transmission models, lubricate the internal yoke splines at the transmission end of the shaft with lithium base grease. The grease should seep out through the vent hole.
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