How to Detect and Replace a Faulty Transmission Valve

January 27, 2012

The transmission valve body is the brain of the transmission. It controls the transmission shifts and directs the appropriate fluids into the appropriate passages to aid in the shifting. All of this enables your transmission to work properly and avoid damaging your entire transmission.

Metal Debris
Metal debris can cause scoring on the fluid passages, which can affect shifts, because proper pressure will not be maintained. Metal debris can also cause the O-rings to fail, causing a fluid leak in your transmission. If metal debris blocks fluid passages, the pressure needed to obtain proper shifts can't be maintained. Different pressures are needed for the valve body to detect which gear you're shifting into. If any of the proper pressures are not met, you could have delayed shifts and/or harsh shifts.

Improper Lubrication
A weak transmission pump can cause improper lubrication in a transmission valve body, which could cause metal to metal contact. This can cause unnecessary wear, causing the gears to stick or fail. Unnecessary wear can cause metal debris, which can lead to other problems. The lubrication also enables the transmission to cool itself, so improper lubrication can lead to overheating.

Worn Fluid
Worn fluid causes the lubrication to lose its viscosity, which decreases the level of protection the transmission fluid passes through. You can easily prevent this by checking and changing your transmission fluid on the appropriate schedule. This is generally every 15,000 to 30,000 miles, unless needed sooner based on the use of your vehicle. If you do a lot of heavy hauling, you work your standard or automatic transmission harder and will need to change the fluids more frequently.

How to Replace a Transmission Valve

The transmission valve, or transmission modulator valve, controls the point at which gears are shifted. The modulator valve works together with the governor or throttle of your engine to determine appropriate speeds for shifting gears. If the transmission modulator valve is faulty, it will usually result in your automatic transmission not being able to shift gears and may also result in a lot of smoke from your transmission or manifold area.

Tools and Materials

  • New transmission modulator valve
  • Hydraulic floor jack
  • Jack stands
  • Set of wrenches

Purchase a Transmission Modulator Valve
Visit your local auto parts store or car dealership that sells your make and model vehicle and purchase a transmission modulator valve that is compatible with your vehicle.

Raise the Vehicle
Using your hydraulic floor jack, raise the vehicle to a height slightly higher than the jack stands that you will use to support the vehicle.

Place jack stands in appropriate support areas to help support the vehicle while you are repairing it. After you have properly positioned the jack stands, lower the floor jack so that the vehicle rest securely on the jack stands.

Remove the Vacuum Hose
Remove the vacuum hose that leads from the intake manifold to the transmission modulator valve. The location of the valve will vary depending on the make and model of your vehicle. Most of the time, the transmission modulator valve is located somewhere near the rear of the transmission. Pull the hose off of the intake manifold and transmission modulator valve and set it aside. Make sure to check the hose to see if any transmission fluid is present. If fluid is present, it is because the diaphragm of the valve has been broken and fluid is being signed into the intake manifold.

Remove the Defective Modulator Valve
Remove the defective transmission modulator valve by removing the bolts from the bracket that holds the modulator valve onto the transmission. You will probably need to remove the valve itself by twisting it counterclockwise and pulling it out. Make sure not to lose the actuating rod that will probably fall out when you remove the modulator valve.

Install the New Transmission Modulator Valve
Place the actuating rod into the hole of the new transmission modulator valve and then carefully insert the valve into the receptacle hole. As you insert the new modulator, you will probably hear a snapping sound which indicates that the O-ring has been sealed. Reinstall the bracket on the modulator and secure it with the bolts.

Reconnect the Hose
Reconnect the vacuum hose to the transmission modulator valve and the intake manifold. Make sure to secure it with any hose clips or clamps that you removed during the hose removal.

Remove the Jack Stands
Raise the vehicle slightly and remove the jack stands. Then, lower the vehicle safely to the garage floor and remove the jack.

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