How a Transmission Valve Body Works

A car's transmission valve body helps control how the gears shift.

A car uses a transmission system to send power generated by the internal combustion engine to other components. The transmission valve body is an integral part of this system.

Shifting

The transmission valve body controls transmission shifting. The transmission valve body contains channels used to direct hydraulic fluid to valves that allow the gears to shift as needed in an automobile.

Clutch Packs and Band Servos

The transmission valve body uses the hydraulic fluid to engage a band servo or clutch pack to shift to the necessary gear. A clutch pack consists of discs that are coupled to the side of the engine, and rotate when the engine is running. A band servo is a hydraulic device that pushes and tightens the transmission brake bands, or bands that create breaking force when tightened around a shaft.

Valves

Valves controlled by the transmission valve body serve a variety of functions. Shift valves, such as the 2-3 shift valve, are responsible for shifting the gear up one level. The manual valve connects to the gear shift handle, and is used to close or open transmission valve passageways according to the current position of the gear shift.

References

• Family Car Parts: A Short Course on Automatic Transmissions
• "Auto Upkeep: Basic Car Care, Maintenance, and Repair"; Michael E. Gray; 2007

Resources

• "How Cars Work"; Tom Newton; 1999