GM Full-Size Trucks 1988-1998 Repair Information

Automatic Transmission

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FLUID RECOMMENDATIONS



Use Dexron lll® or its superseding fluid type.

FLUID LEVEL CHECK



See Figures 1, 2 and 3

Check the level of the fluid at least once a month. The fluid level should be checked with the engine at normal operating temperature and running. 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 the truck on a level surface with the engine idling. Shift the transmission into P and set the parking brake.
  2.  
  3. Remove the dipstick (on newer models, you may have to flip up the handle first), wipe it clean and reinsert if firmly. Be sure that it has been pushed all the way in.
  4.  
  5. Remove the dipstick and check the fluid level while holding it horizontally. All models have a HOT and a COLD side to the dipstick.
  6.  



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Fig. Fig. 1: Remove the dipstick to check the transmission fluid level



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Fig. Fig. 2: Hold the dipstick horizontally and check the fluid level



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Fig. Fig. 3: Use a funnel to add transmission fluid



COLD : the fluid level should fall in this range when the engine has been running for only a short time.
 
HOT : the fluid level should fall in this range when the engine has reached normal running temperatures.
 

  1. Early models have two dimples below the ADD mark, the level should be between these when the engine is cold.
  2.  
  3. If the fluid level is not within the proper area on either side of the dipstick, pour ATF into the dipstick tube. This is easily done with the aid of a funnel. Check the level often as you are filling the transmission. Be extremely careful not to overfill it. Overfilling will cause slippage, seal damage and overheating. Approximately one pint of ATF will raise the level from one notch to the other.
  4.  


WARNING
The fluid on the dipstick should always be a bright red color. It if is discolored (brown or black), or smells burnt, serious transmission troubles, probably due to overheating, should be suspected. The transmission should be inspected by a qualified service technician to locate the cause of the burnt fluid.

DRAIN AND REFILL



See Figures 4, 5, 6, 7 and 8



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Fig. Fig. 4: Loosen all the pan bolts



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Fig. Fig. 5: Pull one corner of the pan down to drain most of the fluid and remove the pan



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Fig. Fig. 6: Remove the old pan gasket and clean both gasket mating surfaces

  1. 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.
  2.  
  3. Place a shallow pan underneath to catch the transmission fluid (about 5 pints). 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. Remove the pan bolts and empty out the pan. On some models, there may not be much room to get at the screws at the front of the pan.
  2.  
  3. 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.
  4.  
  5. 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.
  6.  

To install:
  1. Install a new gasket and filter.
  2.  



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Fig. Fig. 7: Remove the filter from the transmission



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Fig. Fig. 8: Check the condition of the O-ring and replace it as necessary

  1. Install a new gasket on the pan, and tighten the bolts evenly to 18 ft. lbs. (25 Nm) in a crisscross pattern.
  2.  
  3. Add DEXRON®III or its superseding type of transmission fluid through the dipstick tube. The correct amount is in the Capacities Chart. Do not overfill.
  4.  
  5. With the gearshift lever in Park , start the engine and let it idle. Do not race the engine.
  6.  
  7. 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. (6mm) below the ADD mark. Add fluid, if necessary.
  8.  
  9. Check the fluid level after the truck has been driven enough to thoroughly warm up the transmission. If the transmission is overfilled, the excess must be drained off. Overfilling causes aerated fluid, resulting in transmission slippage and probable damage.
  10.  

 
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