Most of the S-10/S-15 trucks equipped with manual transmissions use Dexron® II (or the latest superceding fluid grade) automatic transmission fluid, which is a thin, reddish fluid. However, certain models may be equipped with transmissions which MUST use manual transmission fluid, SAE 80W-90 gear oil, or in some cases, Synchromesh® transmission fluid. Be absolutely sure what type of fluid your transmission requires before changing or adding fluid to the manual transmission. Check your owners manual for the proper recommended fluid for your transmission. If necessary, copy down the transmission codes stamped on the housing and speak with your local parts supplier to verify the type of transmission and the necessary fluid.
Using the incorrect lubricant in your transmission can lead to significant transmission damage and a costly overhaul.
See Figure 1
Remove the filler plug from the side of the transmission (usually located on the passenger's-side of the housing). If the transmission housing contains 2 plugs, the lower is a drain plug, while the upper plug is the filler. The oil should be level with the bottom edge of the filler hole. This should be checked at least once every 6,000 miles or 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.
DRAIN AND REFILL
See Figure 2
Under normal conditions, the manual transmission fluid should not need to be changed. However, if the truck is driven in deep water (as high as the transmission casing) it is a good idea to replace the fluid. Little harm can come from a fluid change when you have just purchased a used vehicle, especially since the condition of the transmission fluid is usually not known.
If the fluid is to be drained, it is a good idea to warm the fluid first so it will flow better. This can be accomplished by 15-20 miles of highway driving. Fluid which is warmed to normal operating temperature will flow faster, drain more completely and remove more contaminants from the housing.
- Raise and support the vehicle safely using jackstands.
- Place a fluid catch pan under the transmission.
- Remove the bottom transmission housing plug and allow the fluid to drain.
- Install the bottom plug and refill the transmission housing through the filler plug.