Before making any linkage adjustments, check the injection timing, and adjust if necessary. Also note that these adjustments should be performed together. The vacuum valve adjustment (THM 350s only) requires the use of special tools. If you do not have these tools at your disposal, refer to the adjustment to a qualified, professional technician.
For most applications, the automatic transmission adjustments on a given transmission should be the same whether it is mated with a gasoline or diesel engine. Subtle differences may occur if the adjustment is somehow related to the fuel system, such as some detent or throttle valve adjustments. The following procedures are for Chevrolet full size vehicles which are equipped with a diesel engine. For additional adjustments which are not listed here, refer to the gasoline adjustments earlier in this section.
- If equipped with cruise control, remove the clip from the control rod, then remove the rod from the bellcrank.
- Remove the throttle valve cable (THM 200) or detent cable (THM 350) from the bellcrank.
- Loosen the locknut on the throttle rod, then shorten the rod several turns.
- Rotate the bellcrank to the full throttle stop, then lengthen the throttle rod until the injection pump lever contacts the injection pump full throttle stop. Release the bellcrank.
- Tighten the throttle rod locknut.
- Connect the throttle valve or detent cable and cruise control rod to the bellcrank. Adjust if necessary.
THROTTLE VALVE (TV) OR DETENT CABLE
Refer to the previous cable adjustment procedures for gasoline engines. Adjust according to the style of cable which is used.
TRANSMISSION VACUUM VALVE
- Remove the air cleaner assembly from the engine.
- Remove the air intake crossover from the intake manifold. Cover the intake manifold passages to prevent foreign material from entering the engine.
- Disconnect the throttle rod from the injection pump throttle lever.
- Loosen the transmission vacuum valve-to-injection pump bolts.
- Mark and disconnect the vacuum lines from the vacuum valve.
- Attach a carburetor angle gauge adapter (Kent-Moore tool J-26701-15 or its equivalent) to the injection pump throttle lever. Attach an angle gauge (J-26701 or its equivalent) to the gauge adapter.
- Turn the throttle lever to the wide open throttle position. Set the angle gauge to zero degrees.
- Center the bubble in the gauge level.
Set the angle gauge to one of the following settings, according to the year and type of engine:
1980 49-50 degrees
- Attach a vacuum gauge to port 2 and a hand-held vacuum pump to port 1 of the vacuum valve (as illustrated).
Apply 18-22 in. Hg (61-74 kPa) of vacuum to the valve. Slowly rotate the valve until the vacuum reading drops to one of the following values:
1980-7 in. Hg (24 kPa)
- Tighten the vacuum valve retaining bolts.
- Reconnect the original vacuum lines to the vacuum valve.
- Remove the angle gauge and adapter.
- Connect the throttle rod to the throttle lever.
- Install the air intake crossover, using new gaskets.
- Install the air cleaner assembly.