You can maximize the effectiveness and durability of your transmission by changing the transmission fluid. Frequency will depend on how your drive your car. If you drive the Mustang under severe conditions, change the transmission fluid at least every 90,000 miles.
Raise the car with a floor jack or ramps. Support it with jack stands. Place a large drain pan beneath the torque converter.
Remove the cover plate from the transmission. Turn the converter until you see the drain plug. Take the rubber access plug off the transmission. Remove the drain plug with a socket wrench. Allow the fluid to drain, and then replace the drain plug, access plug and cover plate.
Place the drain pan beneath the transmission pan. Loosen the pan retaining bolts until they are within a few turns of complete removal. Fluid should drain over the edge of the pan. If it doesn't, tap the pan gently with a rubber hammer to break the gasket seal.
Remove the retaining bolts except for one on each corner. Support the pan with one hand while removing the remaining bolts with the other. Drain the rest of the fluid into the drain pan.
Clean the old gasket with a scraping tool. Discard the old gasket. Clean the transmission pan and the magnet with an appropriate solvent and let them air dry. Don't use a cloth to dry them, because lint can damage the transmission.
Remove the mounting bolts that hold the filter on the transmission. Take off the gaskets or seals. In most cases, you should find a round seal and a rectangular gasket.
Install the new filter assembly, including the seal and gasket and replace the bolts. Install the new gasket onto the oil pan and reinstall the pan on the transmission. Tighten the retaining bolts to 71- to 119-inch pounds with a torque wrench. Return the Mustang to level ground.
Measure the fluid that you drained from the transmission and the torque converter. Remove the dipstick from the filler tube beneath the transmission. Refill the transmission with the new transmission fluid using a funnel.
Start the engine, move the gear selector through the gears and return it to "Park." Allow the engine to run for 15 to 20 minutes so that the engine and transmission can reach normal operating temperature.
Check the transmission fluid level using the dipstick. Add more fluid to bring it to the proper level.
