Understanding the Components of the Transmission Valve Body.

The transmission valve body is made up of three major components:

• The upper valve body.
• The lower valve body.
• The manual valve body.

The transmission’s valves manage fluid direction and pressure. They accomplish this through hydraulic circuits that connect to the main transmission housing. The valves receive oil from the governor, which varies fluid pressure in accordance with vehicle speed.

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Fluid: The Lifeblood of the Transmission
Automatic transmissions became possible only after auto engineers learned how to turn fluid energy into mechanical force, a study known as fluid dynamics. Even in today’s electronic transmissions, fluid under pressure is the key power source that makes the interior components work. The transmission valve body harnesses this force, ensuring that it does the necessary tasks to keep the transmission running.
Types of Valves
The transmission valve body contains several types of valves. These include:
- Pressure Control Valves
These valves control the pressure inside the transmission, including:

• The primary regulator valve: This valve determines the amount of oil flowing from the transmission pump.
• The secondary regulator valve: This valve regulates the pressure of the oil going to the torque converter.
• The oil cooler bypass valve: This valve controls the pressure of the oil going to the oil cooler.
• The pressure relief valve: This valve acts as a “safety switch,” preventing the pressure inside the oil pump from exceeding recommended levels.

- Shift Control Valves  
These valves open and close fluid passages as needed. In modern electronic automobiles, they’re controlled by solenoids, while in older models, they’re driven by hydraulic pressure. They include:

• The manual valve: This valve acts as a master control, directing oil to various areas within the transmission.
• The 1-2 shift valve: This valve regulates shifting from first to second gear and vice-versa.

- Timing valves
These valves work with the shift control valves, ensuring that the transmission moves into the correct speed at just the right moment. In modern transmissions, these valves also help to boost fuel economy, based on data about the owner’s driving habits. They include:

• The downshift timing valve: This prevents accidental downshifting from overdrive.
• The accumulators: These cushion “shift shock” by using spring tension to counter fluid pressure.

- Pressure Modulating Valves  
These valves help to fine-tune the amount of fluid in the transmission at any given time, including:

• The cut-back valve: This regulates throttle pressure as the vehicle speeds up or slows down, ensuring that the pump is always providing the correct amount of oil.
• The governor modulator valve: This reduces the amount of strain the engine places on the transmission at high speeds.

A transmission valve body is like a computer’s central processing unit (CPU). It controls how the transmission works from one moment to the next. Knowing how this system works is vital for effective transmission maintenance. By combining this knowledge with careful troubleshooting techniques, however, no problem is beyond diagnosis or repair.

Posted by ETE Product Support

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