The T-50 transmission is a five-speed overdrive unit that provides increased fuel economy at highway speeds by lowering engine speed. The T-50 transmission has a fifth gear overdrive ratio of 0.861 to 1. This means that the engine turns 0.861 revolutions for every one turn of the transmission output shaft. Four-speed transmissions and fourth gear on the T-50 transmission have a ratio of 1 to 1. The T-50 transmission was used on the 1970 to 1986 Toyota Corolla.
Park the vehicle on a level surface.
Place a drain pan under the transmission to catch the gear oil.
Locate the transmission drain plug. Look at the lower edge of the transmission. You will see (from front to back) three bolts that hold the transmission case halves together, then what looks like a larger bolt. This is the drain plug. Remove it with the crescent wrench. Allow the gear oil to drain for several minutes.
Clean the drain plug and inspect the gasket for damage. If needed, replace the gasket. Install and tighten the drain plug.
Locate the filler plug. It is located directly above the drain plug and looks just like it. Remove it with the crescent wrench. Clean the plug, inspect the gasket for damage and replace it if needed.
Fill the transmission with gear oil through the filler hole up to the bottom of the hole. You will know it's full when gear oil pours back out of the hole. Replace and tighten the filler plug.
It might be a tight fit, but do not raise the vehicle. It needs to be level to get the correct amount of gear oil in it.
Be certain to get the right type of gear oil. Your transmission is designed to use "75W90" gear oil. Your local auto-parts dealer can help you with this.