GM Astro/Safari 1985-1996 Repair Guide

Manual Transmission



Fill the main transmission housing with API GL5 SAE-80W90 Multipurpose Gear Oil for the 4-speed transmission. All of the 5-speed transmissions require the use of Dexron®II (or latest superceding) automatic transmission fluid.


See Figure 1

Click image to see an enlarged view

Fig. Fig. 1: The filler plug is normally found about mid-way up the side of the transmission, while drain plugs are found towards the bottom of the housing (for hopefully obvious reasons)

Remove the filler plug from the passenger's side of the transmission (the upper plug if the transmission has 2 plugs). The oil should be level with the bottom edge of the filler hole. This should be checked at least once every 6000 miles (9700 km) and more often if any leakage or seepage is observed.

When checking the fluid, the vehicle must be level. If it was necessary to raise and support the vehicle to access the filler plug, the vehicle must be supported at sufficient points (all wheels or 4 points on the frame) so it is sitting level and is not tilted forward/backward or to one side.


See Figure 1

Under normal conditions, the transmission fluid should not need to be changed. However, if you purchase a used vehicle, it is usually a good idea to get a clean start with all of the fluids. Also, if the vehicle is operated in high water (up to the level of the transmission) it is definitely a good idea to change the fluid.

  1. Drive the vehicle for a few miles to warm the fluid (so it will flow better).
  3. Raise and support the vehicle safely using jackstands.
  5. Place a fluid catch pan under the transmission.
  7. Remove the bottom plug and drain the fluid.
  9. Install the bottom plug and refill the transmission housing.