The Lexus RX300 was built from 1999 to 2003. It came with a U140F transmission, which is a basic four-speed automatic. The RX300 also came with an optional U140E, which is a four-speed transmission with overdrive. Changing the filter in either transmission is an identical process. The only difference is the fluid capacity of each. This job should take you about two hours if you have never worked on a transmission before. The tools and materials are available at your local auto parts store and your local Toyota or Lexus dealer.
Park the Lexus RX300 on a level area. Chock both rear wheels. Jack the vehicle up underneath the frame. Place the two jack stands underneath the lower control arms of the vehicle. Make sure you rock the vehicle back and forth very gently to ensure that the vehicle is secure.
Place the dripping pan under the rear edge of the transmission pan. Remove the 15 bolts of the pan, starting from the back. Pull the bolts from side to side until the back of the pan drops. The fluid will start to drip out of the back. Leave the front bolts in for about a minute to drain as much out of the back of the pan as possible. Remove the front bolts.
Remove the single bolt that holds the transmission filter in place. Use either a Phillips screwdriver or a socket and ratchet. Place the old filter in your drain pan.
Set the new filter in place. Bolt it back up using about 15 to 20 foot-pounds of torque. Do not overtighten the transmission filter bolt. You could damage the mount or the transmission filter housing itself.
Scrape the gasket material off both the transmission pan and the transmission pan mounting surface. Lightly scrape both surfaces with a straight-razor blade until all of the gasket material and debris are gone.
Spray engine cleaner on a rag and wipe the transmission pan and pan mounting surfaces clean. Do not spray the engine cleaner directly onto or into the pan or the transmission, as this can cause severe damage to the transmission.
Place the new gasket on the mounting surface of the transmission. There should be small pegs protruding from the transmission housing to temporarily hold the new gasket in place.
Wipe out the inside of the transmission pan to remove large debris. Most transmission pans come with a magnet at the bottom for metal particles. Carefully wipe the magnet off and dispose of the rag immediately, as it has sharp metal shards in it that can cut you.
Place the pan back into the mounting position. Tighten the mounting bolts with your hand. Do not tighten or torque any bolts until all of the bolts are snug by hand.
Tighten the bolts of the transmission pan with the 3/8-inch drive ratchet and socket. Torque the bolts to 69 foot-pounds of torque. Do not overtighten the pan bolts, as you will ruin the gasket and not get a proper seal.
Jack up the vehicle higher than the jack stands. Remove the jack stands and lower the vehicle to the ground. Remove the wheel chocks. Add transmission fluid. The U140F transmission takes 4.1 quarts of T-IV automatic transmission fluid, and the U140E uses 3.7 quarts.
Start the engine. Put your foot on the brake and shift slowly through all of the gears. Go through the gears at least two or three times. Shut the engine off.
Recheck the transmission fluid level on the dipstick. Top off the transmission fluid if necessary.
Removing the transmission pan bolts from back to front allows you to control where the fluid is going to come out so you can direct it into the pan. Be sure to use the recommended transmission fluid, which is available at your local Toyota or Lexus dealer.
Transmission fluid is flammable, so don't smoke while changing the filter, and avoid open flames and static electrical charges. When working underneath a vehicle, always make sure that the vehicle is parked on level ground and positioned securely on jack stands.