System Diagnosis - Throttle Valve (TV)

TV pressure controls the shift pattern and the hydraulic line pressure used to apply clutches and bands. If proper line pressure is not available to apply clutch elements and bands, excess slippage may occur during shifting, and the components will be damaged. A TV cable which is damaged, disconnected or improperly adjusted, will cause high or low line pressure which can in turn cause the following conditions: Delayed or harsh upshifts, early upshifts and clutch slippage during shifting, no upshift, chatter on take-off, 1-2 upshift at full throttle only, no full throttle or part throttle detent downshift, and intermittent second gear starts.
Do not attempt to correct a condition by changing the TV cable setting from its proper adjustment. If the TV cable adjustment is ``tailored'' to modify the transmission shift pattern, line pressure may be adversely affected and can cause transmission failure. To diagnose TV system related complaints and ensure proper TV cable adjustment, proceed as follows:
1. Ensure that the engine and all related systems are in proper operating condition.
2. Inspect the TV cable for kinked, binding, disconnected or broken conditions, and replace cable as needed. Also ensure that the proper TV cable is installed.
3. Connect suitable line pressure gauge to transmission and connect tachometer to engine.
4. Run engine until it reaches normal operating temperature, perform the following tests with engine speed at 1000 RPM.
5. Place gear selector in park and record line pressure.
6. Place gear selector in drive and note line pressure reading. Line pressure should be equal to or not more than 10 psi greater than the pressure recorded with selector in park.
7. Manually pull the TV cable to its full length, taking care not to increase the throttle opening and note pressure readings.
8. Pressure should gradually increase as the cable is pulled out and gradually decrease as the cable is returned to its original position, and approximate line pressures should be 55-75 psi minimum and 115-200 psi maximum.
9. Check the T.V system ``fail-safe'' system by disconnecting the TV cable from the throttle lever with the engine running at idle. Line pressure should increase to maximum.
10. Stop engine for at least 30 seconds to take the TV system out of the ``fail-safe'' mode.
11. Connect and adjust the TV cable as outlined, then repeat line pressure checks with selector lever in park and drive. Line pressure should return to normal.
12. If the TV system fails to operate as outlined in the preceding tests, check the following components:
a. Inspect the throttle lever and bracket on the control valve assembly and repair as needed.
b. Check that the TV exhaust valve lifter rod is not distorted or binding in the control valve or spacer plate.
c. Ensure that the TV exhaust check ball moves freely up and down as the lifter is moved.
d. Ensure that the lifter spring holds the lifter rod against the bottom of the control valve assembly.
e. Ensure that the TV plunger does not stick at any position in its range of travel.