FRONT AXLE WILL NOT DISENGAGE INSTALL REV. VACUUM SWITCH

Subject: FRONT AXLE WILL NOT DISENGAGE

Model and Year: 1983-1991 T TRUCKS

Owners of some 1983-1991 T vehicles may comment about inappropriate front axle disengagement. This condition may be due to a corroded transfer case vacuum actuator switch. To correct this condition a revised switch (P/N 1566481 1), constructed of noncorrosive stainless steel, should be installed.

SERVICE PROCEDURE:

The vacuum switch is located on the left upper side of the transfer case (Figure 1).

1. Raise the vehicle and support with suitable safety stands.

2. Remove the vacuum lines from the switch.

3. Remove the corroded switch from the transfer case.

4. Install a revised switch (P/N 1566481 1), coat the threads with thread sealant.

5. Connect the vacuum lines.

6. Lower the vehicle.

7. Check for oil leaks at the threads and vacuum leaks around the vacuum lines.

SERVICE PARTS INFORMATION

Part Number Description ----------- ----------- 15664811 Vacuum Actuator Switch

Parts are currently available from GMSPO.

WARRANTY INFORMATION

For vehicles repaired under warranty use:

Labor Operation: K4120

Use applicable labor time guide for labor hours.

General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.