C6 Automatic Transmission Only:

Figure 2:

Figure 3:

4. C6 Automatic Transmission Only:

Check adjustment of transmission kickdown linkage. Refer to Figures 2 and 3. Adjust kickdown rod as follows:

a. Attach 6 lb. weight to transmission kickdown lever.

b. Rotate throttle to wide open position, c. Insert a 0.060 +/- 0.005 inch spacer between the throttle lever and adjusting screw on the fuel injection pump kickdown lever. If less than 0.060 inch clearance is observed, back off the adjusting screw.

d. Rotate the adjusting screw until contact is made between the screw and the 0.060 inch spacer.

e. Remove the 0.060 inch spacer.

f. Check the gap after the spacer is removed. A gap of 0.010 to 0.070 inch is acceptable.

g. Remove the 6 lb. weight. If the kickdown linkage is out of adjustment, full throttle transmission up-shifts at low engine RPM can result. This would not allow maximum engine RPM and power. Also, the transmission may kick down too quickly, have delayed up-shifts, or no high speed kickdowns if misadjusted.

Figure 4:

Figure 5:

5. C6 Automatic Transmission Only:

Check adjustment of the Vacuum Regulator Valve (VRV). Refer to Figures 4 and 5. On these trucks, a VRV provides a vacuum signal which is proportional to the throttle position, to the transmission vacuum diaphragm. To check the VRV for proper operation and adjustment, the engine must not be running. Proceed as follows:

a. Disconnect the two-port vacuum connector from the VRV located on the left side of the fuel injection pump, see Figure 4.

b. Remove the throttle return cable from the throttle lever on the right side of the fuel injection pump.

c. Remove the throttle cable return springs. Install the end of the spring over the throttle lever ball stud and the other end over the throttle cable support bracket.

d. Attach a vacuum pump with gauge to the upper port of the VRV (the vacuum supply side).

e. Attach a vacuum gauge to the lower port of the VRV (labeled TRANS on the VRV).

f. Apply 20 inches of Hg minimum of vacuum to the VRV and maintain it. It will be necessary to pump vacuum up as it bleeds off. CYCLE THE THROTTLE LEVER FIVE (5) TIMES FROM IDLE TO WIDE OPEN THROTTLE (WOT) WITH VACUUM APPLIED. Insert gauge block, T83T-7B200-AH (0.515 inch), between the pump boss and the throttle wide-open stop, Figure 5. The throttle return spring, as repositioned in step c above, will hold the throttle lever stop against the gauge block. THE VACUUM GAUGE ATTACHED TO THE LOWER PORT OF THE VRV SHOULD INDICATE 6-8 INCHES OF VACUUM. IF THE VACUUM READING IS WRONG. ADJUST THE VRV TO OBTAIN READINGS OF 7 INCHES OF VACUUM.

g. To adjust the VRV, loosen the two screws that attach the VRV to the fuel injection pump, Figure 4. Rotate the VRV until proper vacuum is obtained. When you get the proper vacuum reading, tighten the two screws to 75-90 lb.in. (8-10.5 N-m). If the VRV can't be adjusted to get the proper vacuum, replace the VRV and repeat this procedure starting at step d.

h. Remove the gauge block.

i. Reattach the throttle return spring and the throttle cable.

j. Apply 20 inches of vacuum to the VRV and WHILE MAINTAINING VACUUM, CYCLE THE THROTTLE LEVER FROM IDLE TO WOT FIVE (5) TIMES. The vacuum gauge must indicate at least 13 inches with the throttle at the idle position. If the vacuum gauge indicates less than 13 inches, the VRV must be replaced and the new VRV adjusted per the above procedure.

k. After making the check or adjustment, remove the vacuum pump and gauge from the VRV and reattach the vacuum connector.

l. Start the engine. Check the throttle operation and transmission.