GM Full-Size Trucks 1970-1979 Repair Guide

Drive Axle (Rear and/or Front)

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FLUID RECOMMENDATIONS



Front axles use SAE 80W-90, GL-5 gear lubricant. Rear axles use SAE 80W-90 gear oil. Positraction axles must use special lubricant available from dealers. If the special fluid is not used, noise, uneven operation, and damage will result. There is also a Positraction additive used to cure noise and slippage. Positraction axles have an identifying tag, as well as a warning sticker near the jack or on the rear wheel well.

LEVEL CHECK



See Figures 1, 2, 3 and 4



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Fig. Fig. 1: Using a wire brush, clean the area around the filler filler plug



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Fig. Fig. 2: Use the proper sized ratchet and socket combination and unfasten ...



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Fig. Fig. 3: ... then remove the filler plug from the differential housing cover



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Fig. Fig. 4: Add gear oil to the rear axle through the filler plug

The fluid level in the front axle should be 1 / 2 in. below the filler plug opening. The fluid level in the rear axle should be up to the bottom of the filler plug opening. Lubricant may be added with a suction gun or squeeze bulb.

  1. Park on level ground.
  2.  
  3. Remove the filler plug from the differential housing cover.
  4.  
  5. If lubricant trickles out there is enough. If not, carefully insert a finger and check that the level is up to the bottom of the hole. Locking front hubs should be run in the LOCK position for at least 10 miles each month to assure proper lubrication to the front axle.
  6.  

DRAIN AND REFILL



See Figures 5, 6 and 7



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Fig. Fig. 5: Use a suitable brush to clean off the differential cover



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Fig. Fig. 6: Unfasten the cover retaining nuts ...



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Fig. Fig. 7: ... then carefully pry the cover away and drain the fluid

No intervals are specified for changing axle lubricant, but it is a good idea, especially if you have driven in water over the axle vents.

  1. Park the vehicle on the level with the axles at normal operating temperature.
  2.  
  3. Place a pan of at least 6 pints capacity under the differential housing.
  4.  
  5. Remove the filler plug.
  6.  
  7. If you have a drain plug, remove it. If not, unbolt and remove the differential cover.
  8.  
  9. Replace the drain plug, or differential cover. Use a new gasket if the differential cover has been removed.
  10.  

 
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