Automotive Technology/Automatic Transmission

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

• Automatic Transmission Fluid is red or pink and should be checked regularly

• 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

• Stall Test
• Lockup Torque Converter Clutch

• Engine Vacuum lines leaking at the transmission may consume atf
• Electronic Transmission Control Systems
• Verify start and change systems

Maintenance

• Shift Linkage may become loose or disconnected
• Transmission Range Sensor tells modules the shift linkage position
• Throttle Valve is connected to the pedal by cable linkage
• Kickdown Switch tells the module of Wide Open Throttle condition
• Accumulator
• Band adjustment
• Replace fluid and filter

In Vehicle Service

• Vacuum modulator and system
• Governor Valve
• Seals and gaskets
• Extension Housing Oil Seal
• ATF Cooler
• Speed Sensor and Drive Gear
• Valve Body
• Valve Body Bolt Torque
• Servo
• Accumulator
• Parking Pawl
• Electronic components
• Powertrain Mounts can fail to prevent vibration dampening

Off Vehicle Service

• Engine Core Plugs should be checked for leakage while dismounting transmission
• Transmission Dowel Pins keep position between bell housing and engine block
• Remove Automatic Transmission
• Disassemble Automatic Transmission
• Reassemble Automatic Transmission
• Flex Plate
• Torque Converter

• Oil Pump
• End play and Preload
• Thrust washers and Bearings
• Shafts
• Oil passages
• Bushings
• Planetary Gear assembly
• Transmission case
• Drive Chain
• Final drive components

Friction and reaction units

• Clutch assembly
• Clutch Pack Clearance
• Air test clutch and servo
• One Way Clutch
• Bands and drums

Sample test

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
	Neither