GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Buick 🢒 1997 🢒 Century 🢒 Transmission/Transaxle 🢒 Automatic Transaxle - 4T60-E 🢒 Fluid Leak Diagnosis and Repair

Possible Points of Oil Leaks
  1. Oil may leak from the transmission pan or valve body cover for the following reasons:
    2. • The attaching bolts are not torqued correctly.
    • The gasket is damaged or improperly installed.
    • The oil pan or the mounting face of the valve body cover is not flat.
  2. Oil may leak from the case for the following reasons:
    3. • Servo cover porosity or O-ring damage.
    • The multi-lip seal on the filler tube is damaged or missing.
    • The filler pipe bracket is mislocated.
    • The electrical connector O-ring is damaged.
    • The manual shaft seal is damaged.
    • The oil cooler connector fittings are loose or damaged.
    • The vacuum modulator O-ring is damaged.
    • The axle oil seals are worn or damaged.
    • The park lock out cup plug is loose.
    • The line pressure pickup pipe plug is loose.
    • The bottom pan or side cover gaskets are damaged.
    • The casting is porous.
  3. Oil may leak from the converter end for the following reasons:
    4. • The converter seal is damaged.
       - The seal lip is cut (check converter hub for damage).
       - The bushing has been moved forward and is damaged.
       - A garter spring is missing from the seal.
    • The converter is leaking from a weld area.
    • A casting is porous in the case or the drive sprocket support.
    • The oil seal on the turbine shaft is worn or damaged.
  4. Fluid may come out from the vent pipe under the following conditions:
    5. • Overfilled
    • If the fluid appears milky, water or coolant may be in the fluid.
    • The case is porous.
    • The fluid level indicator registers incorrectly.
    • The drain back holes are plugged.
    • The case to the modulator gasket on the channel plate is mispositioned or damaged.
    •  The thermal element has been set to the incorrect height.

Possible Leak Points
Object Number: 29904 Size: LF
(1)Manual Shaft Seal
(2)Line Pressure Tap
(3)Vent
(4)Vacuum Modulator To Case Seal
(5)Reverse Servo Cover Seal
(6)Case (Porosity/Cracks)
(7)Speed Sensor Seal
(8)Forward Servo Cover Seal
(9)Oil Fill Tube Seal
(10)Axle Seal (Right Hand)
(11)Converter Seal Assembly
(12)Converter (Seams/Cracks)
(13)Bottom Pan Gasket
(14)Cooler Connectors
(15)Case (Porosity/Cracks)
(16)Electrical Connector Seal
(17)Side Cover To Case Gasket
(18)Side Cover To Case Gasket
(19)Side Cover To Channel Plate Gasket
(20)Axle Seal (Left Hand)
(21)Bottom Pan Gasket

Methods for Locating Leaks

You can generally locate and repair the cause of most external leaks with the transmission in the vehicle. Use any one of the following methods for locating leaks:

  1. Thoroughly clean the suspected leak area with a solvent.
  2. Remove the converter shield, if required.
  3. Apply an aerosol type powder such as foot powder to the suspected leak area.
  4. Start the engine and run at fast idle.
  5. Repair leaks and recheck as necessary.
    6. • Identify the type of oil (transmission fluid contains a red dye).
    • Leaking oil is generally carried toward the rear of the car by the air stream.
  6. Drive the car approximately 15 miles to warm up unit to operating temperature 88°C (190°F).
  7. Inspect the car for leaks with the engine running.
  8. Turn the engine OFF, check for leaks caused by drain back.