Hard-Hittin’ Shiftin’

Adjusting Your TV Cable For Maximum Performance

Douglas R. Glad Mar 1, 1999 0 Comment(s)

Step By Step

The TV cable is on the driver-side of this TPI throttle body; notice its upward angle. It will generally be an unshielded cable. Throttle Body Injection (TBI) models have similar characteristics.

Mark the position of the cable housing with a scribe. Gene has pulled the housing out (toward the front of the engine) to demonstrate the relative positions of the cable housing and throttle cable bracket.

At wide-open throttle, the TV cable should be guitar-string tight.

When making an adjustment, push the “D” shaped button on the throttle bracket with a screwdriver and push or pull the cable housing to the desired length.

The 700-R4 is a fine example of a computer-operated transmission with mysterious lock-up converters and wiring harnesses where vacuum modulators should be. Have no fear, these trannies are as simple to adjust as the venerable TH350 and 400.

TV Cable

The simplest adjustment for seat-of-the-pants results is the throttle valve (TV) system controlled by the TV cable. The TV cable attaches to the carburetor or throttle body (TB) on carbureted– tuned port injection– (TPI) and TB–equipped engines. The TV’s function is similar to the vacuum modulator and detent cable of the TH350. If the TV is not properly adjusted, the trans will shift too soon, too soft, too late, or not at all.

To adjust the TV cable you will need a screwdriver, a scribe, a friend, and a late-model Chevy equipped with a 700-R4 (any ’82-and-later rear-wheel-drive car with an overdrive transmission).

Take the car for a testdrive with the shifter in Drive. At light to medium throttle, make a note of the shift-point mph.

Our test car shifted from First to Second at 10 mph and Second to Third at 20 mph. This was a little low, according to Gene Christensen of Auto-Rite Transmissions in Van Nuys, California. He recommended a First-to-Second shift at about 20 mph and a Second-to-Third shift at about 30 mph. To get the car to shift harder and at a higher speeds, the cable housing must be shortened. After this adjustment, the car shifted First to Second at 18 mph and Second to Third at 32 mph with a noticeable improvement in shift firmness.

The next test was making sure the cable wasn’t too short. With the engine off, lift the hood and have your friend try wide-open throttle (WOT) while you watch the TV cable. If the cable is adjusted too short, there will be a clicking sound as the cable housing is forced to lengthen. If this is the case and the car still shifts early, there might be something else in the transmission causing it to shift poorly.

If shortening the cable housing causes harder, later shifts, then the opposite must be true for lengthening it. The longer the cable housing the softer and earlier the shift. When performing this procedure, there is something to be aware of: Detent provides the mechanical leverage causing the transmission to “kick down” or downshift during aggressive throttle stomping or heavy load. The detent enters the equation at the end of throttle travel; if the TV is adjusted too loosely, there will be no kick down. To test this, mat the pedal between 15 and 20 mph and make sure the transmission downshifts from Second to First.

After all the adjustments are made using trial and error and testdrives, make a new scribe mark on the cable housing. Be aware that a broken or disconnected TV will cause the pressure relief ball in the valve body to become fully seated. When this occurs, the transmission will have maximum line pressure, the shifts will occur extremely hard and late, and at lower vehicle speeds the transmission may not shift at all.

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