The transmission filter on a Ford Focus removes debris and sludge from the transmission fluid. While modern transmission flush services back flush the filter and remove many of the trapped contaminants, it’s a good idea to replace the filter every 90,000 to 100,000 miles. While changing the filter isn’t as easy as flushing the transmission, it does not require the specialised flush machine. Thus, if you have basic automotive repair skills, you can change the transmission filter on your Ford Focus yourself in about an hour.
Drive the front wheels of the Focus onto the ramps carefully. Set the parking brake and place the chocks behind the rear wheels to prevent the car from rolling.
Climb underneath with the drop pan and socket set. Place the drop pan directly under the transmission pan.
Loosen the transmission pan bolts until you can pull the pan down far enough to allow the transmission fluid to pour out, into the drop pan. You may need to gently pry the pan away from the transmission with a screwdriver; use care in doing this so you don’t damage the pan or transmission with the tip of the screwdriver.
Remove the pan bolts completely with the socket set and take the pan down. Note the position and orientation of the transmission filter. Grab the transmission filter firmly with both hands and pull it straight down until it disengages from the transmission.
Take the transmission pan and filter out from under the Focus. Clean the transmission pan, especially the sealing surface, with brake cleaner and rags.
Climb back under the Focus with the transmission pan, gasket and new filter. Push the new filter back into place until it seats in the same position and orientation you noted from the old one.
Place the pan gasket on the transmission pan and hold them both up against the transmission. While holding the pan in place, thread the pan bolts back in by hand. Make sure the pan bolts go through the pan, as well as the gasket holes.
Tighten the bolts with the socket set in a crossing pattern. Climb out with the drop pan and socket set.
Open the bonnet and remove the transmission dipstick. Insert the funnel into the dipstick tube and pour five quarts of Mercon V transmission fluid into the funnel.
Start the engine, shift the transmission through all the gears and back to "Park." Check the transmission fluid level and top off as needed until the fluid is in the cross hatch on the dipstick. Move the wheel chocks and drive the Focus off the ramps.