How to Change the Fluid in a Car Transmission

Unbolting the transmission drain pan

Changing the fluid in an automatic transmission can prolong it's lifespan considerably. There are several types of transmission fluid, so it is important to buy the right one.

Things You'll Need

• 5 gallons of automatic transmission
• Socket wrench set
• Drain pan
• Medium-sized funnel
• Transmission filter (optional)
• Transmission drain pan gasket
• High-temp ATV glue (blue or red)
• Floor jack and stands

Instructions

1. Determine what fluid type the vehicle requires. For domestic General Motors or Chrysler products, Dexron III (3) was used on 90 percent of their automatic transmissions. Fords use Type F, which is almost identical to Dexron, but has cleaning solvents added to it. Foreign cars may require a specialized fluid, and their manuals should be checked for the correct type. Standard transmissions normally do not require transmission fluid.

2. Jack up the vehicle's front end and keep it lifted with the jack stands. It only needs to be high enough for drain pan clearance; it may be possible to place the drain pan under the transmission without lifting the car.

3. Locate the transmission fluid check rod (dipstick) in the rear of the engine bay. It will be colored red. Pull this stick out and set it aside, making a note of how the fluid on the stick looks and smells. It should have a sweet, oil smell, not a burnt odor.

4. Unbolt the transmission's drain pan. Several bolts will hold it in place around it's edge. If the vehicle has a drain plug on this pan, then taking the pan cover off is unnecessary. Simply unbolt the plug and let the fluid drain. If the filter is to be changed, this pan cover must come off.

5. Drain the fluid. Once the bolts are loose, fluid will rush out. Take the pan off quickly, and set it and the bolts aside. The red transmission fluid will take a few minutes to fully drain out. Most of the fluid contained in the transmission will not be drained because it is still inside the inner channels of the transmission. Several drains must be done, or a total fluid flush with the car running, to change out all of the fluid.

6. Replace the filter. Directly on the transmission's exposed mechanical interior is a small white filter, held in with a black plastic ring. It pulls out without effort, and can be directly replaced with the new one.

7. Remove and replace the transmission's drain pan gasket. The old one may have been destroyed when removing the pan, or be stuck to the pan or transmission. It is usually a square cork gasket, but some models can use rubber gaskets. If the gasket is cork, clean its area on the pan's outer lip and secure it with a bead of ATV gasket sealant. Line up the bolt holes correctly. Apply another bead of sealant on the top of the gasket, and clean the area where it fits onto the transmission. Rubber gaskets do not need sealant.

8. Replace the transmission's drain pan. Secure the bolts in a staggered pattern, so they do not place too much stress on one side of the gasket. Do NOT tighten them as far as they can go. The gasket will leak if they are overtightened. Finger-tighten them until they are snug, then lightly use the socket wrench to secure them without damaging the gasket.

9. Refill the drained fluid at the dipstick hole. Check beforehand to see how much fluid came out during the drain, and replace about half of that without cranking the engine. Once the funnel does not take any more fluid, or fills slowly, crank the car and continue to pour. With the engine running, the internals of the transmission are pumping fluid into their channels, and it can be filled to its maximum. Check the dipstick often so that the transmission is not overfilled; damage can result.

Tips & Warnings

• Checking of the dipstick's level lines should be done with the engine running.

• Do not overfill the transmission!