The transmission fluid is vital to keeping your BMW's transmission working properly. If your BMW has an automatic transmission, the transmission fluid needs to be changed every 100,000 miles. This means you don't have to change the fluid very often. However, changing the fluid means more than just replacing the liquid itself, as you will also need to clean or replace other components on the transmission.
Drive the BMW for at least 10 miles to warm the transmission up to operating temperature. Park the car on a level surface and apply the parking brake. If you want to raise the car on jack stands, do so at all ends so the car remains level.
Loosen the drain plug for the transmission fluid pan; a half turn with the wrench will be enough. Place a draining container under the pan and remove the plug, Measure the amount of fluid that drains from the pan, then replace the plug with a new plug gasket.
Disconnect the transmission fluid pan by removing its mounting fasteners. Discard its gasket, and clean the mating surfaces and the inside of the pan; brake cleaner will work.
Remove the transmission fluid filter; disconnect its mounting fasteners if equipped. Install a new filter with new seals.
Install the fluid pan back on the transmission, using a new gasket.
Fill the transmission with the fluid specified for your model BMW; the car's manual should state the type needed. Remove the filler/level plug, which is on the transmission above the pan, to fill it with the fluid. Fill it to the amount you measured earlier from the drained fluid.
Check the fluid level; the fluid needs to be just seeping over the edge of the hole. Replace the filler plug, start the engine and let it run idle for a few minutes. Check the fluid level again, as it will have heated and expanded.
