GM Full Size Vans 1967-1986 Repair Guide

Rear Axle Differential

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FLUID RECOMMENDATION



Rear axles use SAE 80W-90 GL-5 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.

FLUID LEVEL CHECK



See Figures 1, 2 and 3



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Fig. Fig. 1: The rear axle filler plug may be in either of the two locations shown here



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Fig. Fig. 2: Remove the filler plug from the housing with a ratchet



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Fig. Fig. 3: If needed, add the fluid through the filler hole

Lubricant levels in the rear axle should be checked as specified in the Maintenance chart. To check the lubricant level:

  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. Front axles should be full up to the level of the hole when warm, and 1 / 2 in. (12.7mm) below when cool.
  6.  

Lubricant may be added with a funnel or a squeeze bulb. Rear axles use SAE 80W-90 GL-5 gear lubricant.

Positraction® limited slip axles must use a 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 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.

DRAIN AND REFILL



See Figures 4 through 8



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Fig. Fig. 4: Use a wire brush to clean the dirt and rust from the differential cover



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Fig. Fig. 5: Unfasten the bolts from the cover



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Fig. Fig. 6: Using a prytool, carefully separate the cover from the case to drain the fluid



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Fig. Fig. 7: After the fluid drains, remove the cover from the case



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Fig. Fig. 8: Cover the differential gears with a rag before cleaning the old gasket from the case

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.  
  11. Lubricant may be added with a suction gun or squeeze bulb. 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. Rear axle lubricant level should be up to the bottom of the filler plug opening.
  12.  

 
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