The following covers Pontiac Bonneville models from 1987 through 1999. Use automatic transmission fluid labeled Dexron III or IIE. Check your vehicle owner's manual to confirm the recommended transmission maintenance schedule. This will vary depending on the type of service under which you operate the car.
Drive the Bonneville about 15 miles to warm the transmission. Park the car on level ground, raise and support it on jack stands and place a large drain pan beneath the transmission. Use an appropriately sized socket wrench to remove the retaining bolts from the front and sides of the transmission fluid pan.
Loosen the rear bolts four turns each. Tap the pan gently with a rubber hammer to break the seal. This will allow fluid to drain out. Remove the remaining bolts when the flow of transmission fluid stops. Carefully remove the pan from the transmission, as some fluid will remain. Pour the remaining fluid into the drain pan. Remove all traces of sealant or gasket from the fluid pan flange.
Inspect the retaining bolts if your Bonneville is a model from 1987 through 1990 to determine whether they're reusable or not. If the flat side of conical washer faces down, away from the head of the bolt, you may reuse them. Otherwise, you need to purchase new bolts.
Take the filter from the valve body. Pry the filter neck out of the seal. You may need special tools J 6215-B and J 21029 or equivalent to remove the seal. Clean the gasket mating surfaces, the boltholes and the bolts with a safe solvent. You can allow them to air dry or dry them with clean lint free cloth.
Coat a new fluid filter seal with petroleum jelly or Transjel. Install the new seal onto the new filter. Install the new fluid filter and seal onto the transmission. Position a new gasket onto the fluid pan. Reinstall the fluid pan onto the transmission. Tighten the bolts in a criss cross fashion. If your vehicle year model falls between 1987 and 1990, tighten the bolts to 15 ft-lb with a torque wrench. If your vehicle year model falls between 1991 and 1999, tighten the bolts to 12 to 13 ft-lb.
Return the Bonneville to level ground. Measure the amount of transmission fluid that you drained from the transmission. Use a funnel to add the same amount of fresh automatic transmission fluid to the transmission through the dipstick filler tube.
Apply the parking brake and block the wheels. Start the engine and move the gear selector through each gear, ending in "Park." Check the fluid level with the dipstick and add more fluid if necessary. You only need to add fluid if the fluid level falls below the crosshatched area on the dipstick. If the fluid level is correct, replace the dipstick, close the hood and turn off the engine.
