Fun With Transmissions - December - 2016

Transmissions 101: Understanding Valve Types

This past October, ATRA was in Las Vegas for the 2016 Powertrain Expo. This year, ATRA presented a series of seminars titled Transmissions 101. The Saturday series started with R&R 101 then to Diagnostics 101 and finished with Transmissions 101.

This series was aimed at entry level technicians who are new to the industry. What surprised all of us was how many industry veterans attended the series, which goes to show that we can all use a little brushing up on the basics every now and then.

In this issue of Fun with Transmissions, we’re going to check out valve bodies and the basic valve types that you’re likely to see in nearly every transmission.

Not all that long ago, transmissions used throttle valves, modulator valves (engine load signals), and governor valves (road speed signal) to control shift timing and feel. Throttle cables and vacuum lines connected the valve body to the engine. The governor valve was attached to the output shaft and supplied the valve body with a pressure signal that varied with vehicle speed. The higher the road speed, the higher the pressure.

Today’s transmissions are completely computer controlled. The engine and transmission have many electronic sensors and computers to control shift timing and feel. That being said, yesterday’s and today’s transmissions have the same basic valves in the valve body.


There are many varieties of valve bodies. Each one looks and functions somewhat differently. But despite these variations, there are only three types of valves:

  1. Regulator — A regulator valve lowers pressure from a higher pressure source. A regulator can have a static setting, producing a constant pressure, or it can vary the pressure output, based on influences from a mechanical force or hydraulic pressure.
  2. Switch — A switch valve works like a light switch: it’s either on or off. It supplies a component or another valve with oil, or it exhausts the oil to the sump. The most common valve of this type is a shift valve. It can direct oil to a shifting element, like a servo or clutch drum, or it can switch oil pressure between two other valves.
  3. Servo — A servo valve moves another valve; either a switch valve or regulator valve.


Regulator Valves — One of the first exercises in understanding valve function and oil schematic interpretation is identifying the three types of valves.

The regulator valve is the most common, but the most difficult to recognize because there are several types of regulators. There are two properties common to all regulators that will help you identify them:

  1. Nearly all regulators use a spring (the only exceptions are a few governors.
  2. They use source pressure to move the valve toward the spring.

All regulators require a balance system to maintain regulation. Most balance systems take pressure that the regulator has modified and apply it to an area of the regulator. This balance pressure works on the valve to move it toward the spring.

Here are three basic regulators. In the first example, the balance oil is regulated pressure that is diverted to the end of the valve (figure 1).

A common example of this type of regulator valve at work is the solenoid regulator valve in a 6F35N and the actuator feed limit valve in a 6L80E (figure 2). Although these valves have different names, they both perform the same function: To regulate feed oil to the shift solenoids. Also both of these valves are very prone to valve bore wear, which can cause shift and engagement issues. Be sure to take extra care when inspecting these valves and the bores.

The second regulator uses an internal balance system: Pressure isn’t diverted to the end of the valve; instead, the pressure goes between two of the lands on the valve. Since the land closer to the spring is larger, the force created by hydraulic pressure pushes the valve toward the spring (figure 3). The third type of regulator is a main pressure regulator, which operates by bleeding off pressure directly from the pump feed to maintain a balanced pressure. The source pressure for the main pressure regulator originates from the pump, rather than a regulated source. These main pressure regulators use mainline pressure to provide balance pressure. This prevents the entire system from exceeding the level set for the system (figure 4).

Switch Valves — Switch valves, as their name implies, switch oil on or off. They can direct oil to a shifting element or another valve. Switch valves don’t vary pressure like a regulator; they’re either open or closed. Typically, when a switch valve closes a circuit, it will also open that circuit to exhaust.

There’s one property of a switch valve that makes it easy to identify: A switch valve doesn’t use source pressure to move the valve. There’s always some other Figure 5 force that moves the valve. The next two examples show two basic switch valves. In the first example, the valve is controlled mechanically. This is usually what you’d see in a manual valve or detent valve (figure 5).

In the second example, the switch valve is controlled by some other pressure (typically from a shift solenoid). This is usually the arrangement for shift valves (figure 6). Common examples of switch valves are 4L60E shift valves, which are controlled by the shift solenoids.

Servo Valves — Servo valves serve one main purpose: To move other valves. But sometimes a manufacturer will also use a servo valve as regulator or a switch. You may want to consider these combination valves.

A combination valve then can be referred to as a servo/switch valve, or a servo/regulator valve, but its primary function is a servo valve (figure 7).

Switch Valves that Regulate Pressure — Many units today control line pressure using a pulse width modulated solenoid. These solenoids are energized and de-energized very quickly, which regulates the pressure applied to one side of a switch valve. This causes the switch valve to float between wide open and full closed, regulating the pressure to the circuit. Even though these valves regulate pressure, they’re still considered switch valves.

In figure 8, the solenoid is receiving a pulsed signal. These pulses are so fast, they cause the switch valve to float between open and closed, causing the valve to work as a regulator.

The Ford 6R60 valve body uses this type of solenoid/switch valve to apply the clutches. This allows the computer to apply and release the clutches with great accuracy.

When we joined this industry, some of us came through family, some through tech schools (like me), and some needed a job and started sweeping floors and worked our way up through the ranks.

Transmission work is something that is learned by doing. Yes, you need a basic mechanical aptitude to do this work and a determination to learn. When you learn, you become an asset to your shop.

Knowing which types of valves are which, what they do, and how they perform will help when things don’t go right, or — and this is a biggie — when you’re working on a vehicle that “just doesn’t feel quite right.”

And we all know that when things go right and feel right with the cars we’re working on, it’s much easier to have fun with transmissions!