Many cars with automatic transmissions use a mechanical cable that runs from the transmission to the throttle linkage. This throttle valve cable is responsible for controlling the throttle lever providing movement to the car. The throttle valve cable is used to control the line pressure, downshifting and the feel of the shifting. When the throttle valve cable is out of specification, the transmission can shift early, shift late or not shift at all.
Before the throttle valve cable can be adjusted, the transmission must be in good working order. First, you will need to find out if the transmission is faulty or if the transmission just needs to be adjusted.
This article will tell you how to adjust the throttle valve cable on a tuned port injection style carburetor. Mechanical carburetors and fuel injected vehicles can be adjusted in a similar manner with the exception of part locations.
Warning: Improperly adjusting the throttle valve cable can cause extensive damage to the transmission. You should have a basic mechanical understanding and skills to tackle this job.
Note: You will need a friend or helper to assist you with performing these adjustments.
Part 1 of 2: Test drive and determine how much to adjust the throttle
- Owner's manual
Step 1: Perform a test drive. Get a friend to accompany you on a test drive of your vehicle.
Ask your helper to note the MPH of each shift point. Limit the acceleration to light and medium levels for the most accurate results. Take note of how hard or soft the transmission shifts. This information will be your baseline for any changes made.
Step 2: Locate the throttle linkage. Before you can make any adjustments, you will need to locate the throttle valve adjustment location and the throttle linkage.
Pop the hood and look for the intake piping. Follow the piping to the intake itself. You will find a series of linkages and cables mounted on the intake. The one pictured above is an example of the throttle valve linkage. Your vehicle may look different depending on the make and manufacture.
Part 2 of 2: Adjust the Throttle Valve Cable
Step 1: Mark the current cable length. Using a marker, mark the cable housing’s current location. This is so that you have a reference point to fall back to in case something goes wrong.
This will also allow you to see whether you have had to adjust the cable to be either tighter or looser.
Step 2: Check the cable at wide open throttle. Have your helper sit in the driver's seat and push the gas pedal to the floor. You will see the throttle linkage move all the way in one direction. This is called wide open throttle (WOT).
Now with the throttle wide open, test the tautness of the throttle linkage. The cable should be tight with the housing extended, without any slop.
Step 3: Adjust the cable. Keeping the cable relaxed, push in the D button with a screwdriver. When the D button is pressed, the cable housing can be moved closer to the throttle bracket to tighten the cable or further away to loosen it.
- Note: Make sure that the gas pedal is not being depressed while you are making the adjustments.
- Tip: Consult the owner's manual for any specifications for your car’s make and model.
Adjust the cable by a small increment then have your helper press the gas pedal all the way down and check the cable at WOT. Lengthening the cable will allow the vehicle to shift earlier and the shift will be softer. Shortening the cable will have later shifts that are harder.
You may have to repeat the adjustment process until it is set right.
Step 4: Perform a final check and then test drive. Look over your work and make sure everything is tightened and nothing is left disconnected or loose. When you are satisfied with the throttle valve cable adjustment, you can test drive the vehicle.
Drive with light to moderate acceleration and ask your helper to note down and check the shift feel and the MPH of the shift points. Compare these to the original readings and any specifications provided in the owner's manual for your car.
Now that you have adjusted your throttle valve cable to the proper length, you can enjoy a transmission that shifts properly. This will also contribute additional life to the transmission. The proper shift points and feel can improve fuel economy and the drivability of the vehicle.
Adjusting the throttle valve cable can seem like a daunting matter. If at any point you have any questions, YourMechanic has qualified Technicians standing by to answer any questions you may have.
If you are uncomfortable performing this service on your own, get one of our certified mechanics from YourMechanic to adjust the throttle valve cable for you.
This article originally appeared on YourMechanic.com as How to Adjust a Throttle Valve Cable and was authored by Spencer Clayton.