Automotive Technology/Automatic Transmission

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Automatic transmission (U.S.) Automatic gearbox (U.K.) In British English in this context the word Transmission refers to the whole driveline and includes driveshafts and the differential (if housed seperately) and will include the transfer box in four-wheel drive vehicles.

Working with an automatic transmission can be expensive and difficult. Transmissions often require special tools to disassemble and assemble. The weight of a transmission alone requires safety procedures

They are considered to be more complex than engines, because of the valve body and solenoid controls. Planetary gears are complex and puzzle-like. Every piece, especially thrust washers fit one way. You can check the clearances when you're done assembling the transmission.

Automatic Transmission Diagnostics[edit | edit source]

  • Vibration and Noise
    • Vibration usually comes from the output shaft or torque converter
    • Noise is usually related to gear and engine speed
  • Pressure Test can be used to read pressure during operation, design permitting
    • should be used when shifts are rough or shift timing is wrong
  • Engine Vacuum lines leaking at the transmission may consume atf
  • Electronic Transmission Control Systems
  • Verify start and change systems

Maintenance[edit | edit source]

In Vehicle Service[edit | edit source]

Off Vehicle Service[edit | edit source]

Friction and reaction units[edit | edit source]

Sample test[edit | edit source]

A vehicle is brought in with an automatic transmission that won't downshift from cruising speed (forced downshift). Technician A says that the throttle valve cable may be out of adjustment. Technician B says that the kickdown switch may be open. Who is right?

A only
B only
Both A and B