According to General Motors, the manual transmission fluid on 1984-88 Corvettes, equipped with the 4-speed manual transmission (with automatic overdrive), does not require changing. However the fluid in the overdrive unit must be changed every 30,000 miles (50,000km). Dexron® II, or its latest superseding grade of automatic transmission fluid is the only type of fluid that can be used on these vehicles. The use of any other fluids or additives may damage the transmission.
On 1989-96 vehicles, equipped with the 6-speed manual transmission, General Motors does not give an interval for changing the fluid. The only service required is to check the fluid level and add if necessary. The required fluid on this vehicle is manual transmission fluid SAE 5W-30, GM part no. 1052931, or equivalent gear lubricant.
To check or add fluid to the manual transmission on these vehicles, perform the following:
- Carefully raise the car and support on jackstands as close to level as possible.
- Clean the dirt and/or foreign material from around the filler plug, then remove the filler plug.
- If lubricant begins to trickle out of the hole, there is enough and you need not go any further. Otherwise, carefully insert your finger (watch out for sharp threads) and check to see if the oil is up to the edge of the hole.
- If not, add the proper type of oil through the hole until the level is up to the edge of the hole.
- Install and tighten the filler plug to 26 ft. lbs. (35 Nm).
DRAIN & REFILL
See Figure 1
To drain the overdrive unit and replace the oil filter, perform the following procedure.
- Raise and safely support the vehicle.
- For convertibles, remove the upper and lower underbody braces.
- Place a suitable drain pan under the overdrive oil pan, then remove the pan attaching bolts from the front and sides of the pan.
- Loosen the rear pan bolts about 4 turns each.
- Carefully pry the pan loose, allowing the fluid to drain into the pan.
- Unfasten the remaining bolts, then remove the fluid pan.
- Drain any fluid remaining in the pan into the drain pan. Remove and clean the pan magnet. Clean the fluid pan with a suitable solvent, then allow to dry thoroughly .
- Unfasten any necessary retainers, then remove the filter from the transmission.
- Install a new filter and secure with any necessary retainers.
The case and pan flange surfaces must be free of oil before applying the RTV sealant.
- Install the magnet in the oil pan as shown in the accompanying figure. Apply a bead of RTV sealant to the oil pan flange, then place the pan in position while the RTV is stills wet. The bead of RTV should be applied as shown in the accompanying figure.
- Install the oil pan-to-case bolts and tighten to 6-8 ft. lbs. (8-10 Nm).
- Fill the overdrive unit with Dexron® III, or equivalent automatic transmission fluid.
- For convertibles, install the upper and lower underbody braces.
- Carefully lower the vehicle.
See Figures 2, 3 and 4
On these vehicles, the fluid in the manual transmission does not require changing. If you do choose to change the transmission fluid, perform the following procedure. The transmission fluid should be drained after a short period of operation when the oil is warm. This allows any existing moisture absorbed by the oil to be expelled when the oil is drained.
- Raise and safely support the vehicle with safety stands.
- Clean the dirt and oil from around the fill plug and the oil drain plug.
- Remove the oil fill plug.
- Position a suitable drain pan under the oil drain plug and allow the oil to drain into a suitable container.
- Install the oil drain plug and tighten to 26 ft. lbs. (35 Nm).
- Fill the transmission with the proper type and amount of fluid to the level of the fill plug, then install the plug.
- Carefully lower the vehicle.