TRANS. CASE 'SELF-ENGAGEMENT' 4-WHEEL DRIVE W/DUAL R. WHEELS

VEHICLES AFFECTED: 1989 K3 TRUCKS WITH R05 (DUAL REAR WHEELS)

Some 1989 K3 trucks with dual rear wheels may experience a transfer case condition which may be described by the operator as "self engagement." The condition occurs as the vehicle is being driven in two wheel high. The driver may comment that the four wheel drive indicator lights up and the front axle tries to engage. Typically, this condition is temporarily corrected if the transfer case is shifted into four wheel drive and then back to 2 HI. The cause of this condition has been identified as the transfer case switch, which may become pressurized during temperature increases and can close the switch contacts.

PRODUCTION CHANGE:

A revised switch is available which incorporates pressure relief grooves into the ball seat area to prevent pressurization (Figure 1). The part number for the new switch is listed below. The revised switch was put into production during the 1989 model year. Vehicles which have the new design switch can be identified by the serial number on the transfer case identification tag. An example of the tag and its location on the transfer case is shown in Figure 2. Vehicles with transfer case serial numbers equal to or higher than those given below have the new design switch.

Transfer Case Model Serial Number Breakpoint ------------------- ------------------------ 1370-001 1628

1370-002 1338

SERVICE PROCEDURE:

If the condition described above is encountered, the switch should be replaced, and an evaluation of the front axle should be made to determine if any damage to components has occurred. The parts most likely to be affected are the solenoid housing (5), solenoid (10), shift shaft (18), sleeve (22), and output shaft (23), see figure 3.

The front axle fluid should be changed even if no damage is evident when the original switch is replaced.

SERVICE PARTS INFORMATION:

Revised switch part number

15634402

Use most applicable labour operation and time from the Canadian Labour Time Guide.

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.