GM Throttle Valve (TV) Cable Adjustment

GM, as well as some other manufactures, has a number of automatic transmissions "out there", that, instead of having a vacuum modulator to sense engine load, use a Throttle Valve Cable, attached to the throttle linkage; When the throttle is depressed, the cable is "pulled" progressively with throttle position. In addition to providing forced downshifts (kickdown), and progressively later (higher speed) upshifts at higher throttle settings, the throttle valve also adjust main line pressure in the transmission. Operating a transmission with the TV cable out of adjustment, can, not only produce early, or late upshifts, but incorrect line pressure, as well. What this means, in simple terms, is that TV pressure that is too low, will produce main line pressure that is also too low, and will eventually "burn" the transmission clutches.

Before a transmission is test driven (after installation) a preliminary adjustment must be made, and then "fine tuned" during the test drive. Adjust the cable so that it will be pulled all the way, when the throttle is simultaneously opened all of the way (with the engine turned off, of course). Make sure that the cable returns (with no binding) when the throttle is released. This preliminary adjustment will frequently be too "high", and the throttle pressure will have to be reduced, to attain proper shift points. I prefer to start with an adjustment that is "too high", and then work down, rather than "too low" and work up.

A "bird's eye view" of GM throttle cable adjustment

To raise throttle pressure (and raise shift points, and make "kickdown" more responsive) move the cable housing towards the rear (away from the throttle linkage), as you simultaneously depress the button on the cable housing (on GM models). Other manufactures have similar adjustments; Toyota, for instance, uses a "double nut" arrangement, but the same principals apply; move the cable housing away from the carburetor to increase throttle pressure. Move the cable housing adjustment a small amount at a time (1/16", or so); a small adjustment can often make a world of difference. Naturally, to lower the pressure (and lower shift points, and make "kickdown" less sensitive), move the cable housing towards the throttle linkage.

Now, if you have a Chrysler product you also probably have a "TV" system, but most (probably yours) has a TV rod (as well as most Ford AOD transmissions), which "pushes", rather than a cable, that pulls. Similar principals hold true, but to raise throttle pressure, you must lengthen the rod, so it pushes farther, and shorten the rod to lower throttle pressure.