//bottom ads

GM Blazer/Jimmy/Typhoon/Bravada 1983-1993 Repair Guide

Vacuum Servo


See Figure 1

Most factory or dealer installed cruise control systems for these vehicles utilize a vacuum servo to rotate the throttle plate and hold engine speed. The servo is connected to the throttle plate by linkage, either a chain, rod or cable.

Click image to see an enlarged view

Fig. Fig. 1: Cross-sectional view of a common servo unit


See Figures 2 and 3

  1. Disconnect the negative battery cable.
  3. Disengage the electrical connector(s) from the servo, as applicable.
  5. Disconnect the vacuum line from the servo assembly.

Click image to see an enlarged view

Fig. Fig. 2: Servo mounting - early model 2.5L engine

Click image to see an enlarged view

Fig. Fig. 3: Common early servo mounting - TBI V6 engine

  1. Disconnect the servo linkage.
  3. On some late model vehicles, it is necessary to remove the cruise control cable. See the procedure later in this section.
  5. Unfasten the servo and bracket assembly retaining bolts, then remove the servo from the vehicle.

To install:
  1. Install the servo and bracket assembly, then secure using the retaining bolts.
  3. If removed, install the cruise control cable.
  5. Connect and adjust the servo linkage.
  7. Install the vacuum line to the servo assembly.
  9. Engage the necessary electrical connector(s).
  11. Connect the negative battery cable.


See Figures 4 and 5

The vacuum servo linkage is usually adjusted either by jamnuts or by a servo blade which contains various adjustment holes. In either case, once the engine is fully warmed, position the cable or rod so it is tight, with little slack, but NOT holding the throttle open. For vehicles equipped with the servo blade, if the desired hole seems to open the throttle, take the next hole on the blade in order to leave the required slack. It would be better for the adjustment to be on the loose side rather than on the tight side of proper adjustment.

Click image to see an enlarged view

Fig. Fig. 4: Common late model servo mounting

Click image to see an enlarged view

Fig. Fig. 5: Common vacuum hose routing - TBI V6 engine