GM Full-Size Trucks 1970-1979 Repair Guide

Front Hub

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The following procedures are applicable to 4-wheel drive models only.

See Figures 1, 2 and 3

Locking front hubs are standard equipment on 1975 and later 4-wheel drive models and optional on earlier years, with the exception of 1973-79 full time 4-wheel drive trucks. The purpose of locking hubs is to reduce friction and wear by disengaging the front axle shaft, differential, and driveline from the front wheels when 4-wheel drive is not being used.

The engagement and disengagement of the hubs is a manual operation which must be performed to each hub assembly. Unlocking should only take place when the transfer case lever is in the two wheel drive position. The hubs should be placed in the full Lock or full Free position or damage will result.


WARNING
Do not use 4-wheel drive unless the hubs are in the Lock position. Locking hubs should be run in the Lock position for at least 10 miles each month to assure proper differential lubrication.



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Fig. Fig. 1: Exploded view of the manual-locking free wheeling hubs



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Fig. Fig. 2: Exploded view of the automatic free wheeling hubs



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Fig. Fig. 3: Exploded view of locking hubs for 1970-77 K-20 and K-2500 models

REMOVAL & INSTALLATION



See Figures 4 and 5



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Fig. Fig. 4: Removal of the spindle



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Fig. Fig. 5: Removing the spring thrust washer and spindle

This procedure requires snapring pliers and a special hub nut wrench. It is not very easy without them.

  1. Raise and support the front end on jackstands.
  2.  
  3. Remove the wheels.
  4.  
  5. For 1970 and later 1 / 2 and 3 / 4 ton trucks with locking front hubs, lock the hubs. Remove the outer retaining plate Allen head bolts and take off the plate, O-ring, and knob. Take out the large snapring inside the hub and remove the outer clutch retaining ring and actuating cam body. This is a lot easier with snapring pliers. Relieve pressure on the axle shaft snapring and remove it. Take out the axle shaft sleeve and clutch ring assembly and the inner clutch ring and bushing assembly. Remove the spring and retainer plate.
  6.  
  7. For 3 / 4 ton truck models 1970-76, with locking front hubs, turn the hub key to the Free position. Remove the Allen head bolts securing the retainer cap assembly to the wheel hub. Pull off the hub cap extension housing and its gasket.
  8.  

You will have to modify this procedure for either of the models mentioned above if you have non-factory installed locking hubs.

  1. If you don't have locking front hubs, remove the hub cap and snapring. Next, remove the drive gear and pressure spring. To prevent the spring from popping out, place a hand over the drive gear and use a screwdriver to pry the gear out. Remove the spring.
  2.  
  3. Remove the wheel bearing outer lock nut, lock ring, and wheel bearing inner adjusting nut. A special wrench is required.
  4.  
  5. Remove the brake disc assembly and outer wheel bearing. Remove the spring retainer plate if you don't have locking hubs. **see Section** 9 for details on brake drum or disc and caliper removal.
  6.  
  7. Remove the oil seal and inner bearing cone from the hub using a brass drift and hammer. Discard the oil seal. Use the drift to remove the inner and outer bearing cups.
  8.  
  9. Check the condition of the spindle bearing. If you have drum brakes, remove the grease retainer, gasket, and backing plate after removing the bolts. Unbolt the spindle and tap it with a soft hammer to break it loose. Remove the spindle and check the condition of the thrust washer, replacing it if worn. Now you can remove the oil seal and spindle roller bearing.
  10.  

The spindle bearings must be greased each time the wheel bearings are serviced.

  1. Clean all parts in solvent, dry, and check for wear or damage.
  2.  
  3. Pack both wheel bearings (and the spindle bearing) using wheel bearing grease. Place a healthy glob of grease in the palm of one hand and force the edge of the bearing into it so that grease fills the bearing. Do this until the whole bearing is packed. Grease packing tools are available to make this job easier.
  4.  
  5. To reassemble the spindle: drive the repacked bearing into the spindle and install the grease seal onto the slinger with the lip toward the spindle. It would be best to replace the axle shaft slinger when the spindle seal is replaced. See Axle Shaft procedures for details.
  6.  

An improved spindle seal (no. 376855) and axle seal (no. 376851) were introduced during the 1976 model year. These can be installed on earlier (late 1972 and up) models.

  1. If you are using the improved seals, fill the seal end of the spindle with grease. If not, apply grease only to the lip of the seal. Install the thrust washer over the axle shaft. On late 1972 through 1982 models, the chamfered side of the thrust washer should be toward the slinger. Replace the spindle and tighten the nuts to 45 ft. lbs. (61 Nm) for vehicles through 1976, to 25 ft. lbs. (34 Nm) for 1977-78 vehicles, or to 33 ft. lbs. (45 Nm) for 1979 vehicles.
  2.  

WHEEL BEARING ASSEMBLY AND ADJUSTMENT



  1. To reassemble the wheel bearings: drive the outer bearing cup into the hub, replace the inner bearing cup, and insert the repacked bearing.
  2.  
  3. Install the disc or drum and outer wheel bearing to the spindle.
  4.  
  5. Adjust the bearings by rotating the hub and tightening the inner adjusting nut to 50 ft. lbs. (68 Nm), then loosening it and retightening it to 35 ft. lbs. (47 Nm). Next, back the nut off 3 / 8 turn or less. Turn the nut to the nearest hole in the lockwasher. Install the outer locknut and tighten to a minimum of 50 ft. lbs. (68 Nm) for vehicles through 1978, or to 80 ft. lbs. (108 Nm) for 1979 vehicles. There should be 0.001-0.010 in. bearing end-play. This can be measured with a dial indicator.
  6.  
  7. Replace the brake components.
  8.  
  9. Lubricate the locking hub components with high temperature grease. Lubrication must be applied to prevent component failure. For 1970-79 1 / 2 ton and 1977-79 3 / 4 and 1 ton models, install the spring retainer plate with the flange side facing the bearing over the spindle nuts and seat it against the bearing outer cup. Install the pressure spring with the large end against the spring retaining plate. The spring is an interference fit; when seated, its end extends past the spindle nuts by approximately 7 / 8 in. Place the inner clutch ring and bushing assembly into the axle shaft sleeve and clutch ring assembly and install that as an assembly onto the axle shaft. Press in on this assembly and install the axle shaft ring. If there are two axle shaft snapring grooves, as on 1976-79 models, use the inner one.
  10.  

You can install a7/16in. bolt in the axle shaft end and pull outward on it to aid in seating the snapring.

  1. Install the actuating cam body in the cams facing outward, the outer clutch retaining ring, and the internal snapring.
  2.  
  3. Install a new O-ring on the retaining plate, and then install the actuating knob in the Lock position.
  4.  
  5. Install the retaining plate. The grooves in the knob must fit into the actuator cam body. Install the seals and six cover bolts and tighten them to 30 ft. lbs. (41 Nm). Turn the knob to the Free position and check for proper operation.
  6.  
  7. For 1970-76 3 / 4 and 1 ton models, apply grease generously to the axle splines and teeth of the inner and outer clutch gears.
  8.  

Remove the head from a 5 in. long3/8in. bolt and use this to align the hub assembly.

  1. Install the headless bolt into one of the hub housing bolt holes. Install a new exterior sleeve extension housing gasket, the housing, and a new hub retainer cap assembly gasket, and the cap assembly.
  2.  
  3. Install the six Allen head bolts and their washers, and tighten them to 30 ft. lbs. (41 Nm). Turn the knob to Lock and check engagement.
  4.  
  5. Without locking hubs, replace the snapring and hub cap. If there are two axle shaft snapring grooves, as on 1976-79 vehicles, use the inner one.
  6.  

 
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