GM Full-Size Trucks 1980-1987 Repair Guide

Automatic Transmissions

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FLUID RECOMMENDATIONS



The correct fluid to use in the automatic transmission is DEXRON®II.

LEVEL CHECK



See Figure 1

Check the level of the fluid at the specified interval. The fluid level should be checked with the engine running and at normal operating temperature. If the truck has been running at high speed for a long period, in city traffic on a hot day, or pulling a trailer, let it cool down for about thirty minutes before checking the level.

  1. Park on a level surface with the engine running and the shift lever in Park.
  2.  
  3. Remove the dipstick at the rear of the engine compartment. Cautiously feel the end of the dipstick with your fingers. Wipe it off and replace it, then pull it again and check the level of the fluid on the dipstick.
  4.  
  5. If the fluid felt cool, the level should be between the two dimples below ADD. If it was too hot to hold, the level should be between the ADD and FULL marks.
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  7. If the fluid is at or below the ADD mark, add fluid through the dipstick tube. One pint raises the level from ADD to FULL when the fluid is hot. The correct fluid to use is DEXRON®II. Be certain that the transmission is not overfilled; this will cause foaming, fluid loss, and slippage.
  8.  



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Fig. Fig. 1: Automatic transmission dipstick markings

DRAIN AND REFILL



See Figures 2 through 12

Some automatic transmissions are equipped with drain plugs to facilitate fluid changes, but most transmissions require that the pan be removed in order to drain the fluid. This is done partially to discourage fluid changes without changing the filter.

The fluid should be drained with the transmission warm. It is easier to change the fluid if the truck is raised somewhat from the ground, but this is not always easy without a lift. The transmission must be level for it to drain properly.

  1. In order to protect the transmission components, clean the fluid pan and surrounding area before removing the pan.
  2.  
  3. Place a drain pan underneath to catch the transmission fluid (at least 5 pints). On earlier models, the transmission pan has a drain plug. Remove this and drain the fluid. For later models, loosen all the pan bolts, then pull one corner down to drain most of the fluid. If it sticks, VERY CAREFULLY pry the pan loose. You can buy aftermarket drain plug kits that makes this operation a bit less messy, once installed.
  4.  

If the fluid removed smells burnt, serious transmission troubles, probably due to overheating, should be suspected.

  1. If necessary for access, remove the torque converter cover and/or lower the crossover pipe by disconnecting it from the exhaust manifolds.
  2.  
  3. Remove the pan bolts until 1 end of the pan may be lowered to begin draining the fluid. Once the level has dropped sufficiently to prevent excessive spillage, remove the retaining bolts, carefully lower the pan and empty the remaining fluid. On some models, certain pan bolts may be difficult to reach without U-joint or wobble extensions
  4.  
  5. Clean the pan with solvent and allow it to air dry. If you use a rag to wipe it out, you risk leaving bits of lint and threads in the transmission.
  6.  
  7. Remove the filter or strainer retaining bolts. On the Turbo Hydra-Matic 400, there are two screws securing the filter or screen to the valve body. A reusable strainer may be found on some models. The strainer may be cleaned in solvent and air dried thoroughly. The filter and gasket must be replaced.
  8.  
  9. Install a new gasket and filter.
  10.  
  11. Install a new gasket on the pan, and tighten the bolts evenly to 12 ft. lbs. in a criss-cross pattern.
  12.  
  13. Add DEXRON® or DEXRON®II transmission fluid through the dipstick tube. The correct amount is in the Capacities Chart. Do not overfill.
  14.  
  15. With the gearshift lever in PARK, start the engine and let it idle. Do not race the engine.
  16.  
  17. Firmly set the parking brake.
  18.  
  19. Move the gearshift lever through each position, holding the brakes. Return the lever to PARK, and check the fluid level with the engine idling. The level should be between the two dimples on the dipstick, about 1 /4 in. below the ADD mark. Add fluid, if necessary.
  20.  
  21. Check the fluid level after the truck has been driven enough to thoroughly warm up the transmission. Details are given under Fluid Level Checks earlier in the section. If the transmission is overfilled, the excess must be drained off. Overfilling causes aerated fluid, resulting in transmission slippage and probable damage.
  22.  



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Fig. Fig. 2: On all rear wheel drive vehicles, the transmission is bolted directly behind the engine. Note the engine oil and transmission fluid pans in the center of the photograph



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Fig. Fig. 3: If necessary for additional clearance, remove the torque converter cover



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Fig. Fig. 4: Clean the drain pan and surrounding area to prevent transmission contamination and damage



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Fig. Fig. 5: A U-joint is necessary to loosen some of the more difficult to reach bolts, such as these at the rear of the pan



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Fig. Fig. 6: With the bolts removed and the pan partially drained, carefully lower the pan from the vehicle



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Fig. Fig. 7: If the old gasket remained in place, be sure to remove all traces of it from the transmission and fluid pan



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Fig. Fig. 8: Support the filter by hand and remove the retaining screws



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Fig. Fig. 9: With the screws removed, lower the old filter from the transmission. Be careful as the filter will likely still contain fluid



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Fig. Fig. 10: Place the new gasket onto the replacement filter



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Fig. Fig. 11: Hold the new filter in position and secure using the retaining screws



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Fig. Fig. 12: Add automatic transmission fluid through the automatic transmission dipstick tube using a funnel

 
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