FRONT AXLE ENGAGEMENT OR OPERATION

MODELS: 1988 K MODEL

THIS BULLETIN SUPERCEDES DCS MESSAGE 1988 K-1, 2, 3 SIERRA TRUCKS DATED JANUARY 6,1988 PARTS WILL BE AVAILABLE FROM GMSPO ON MARCH 15,1988

If the front axle does not engage or becomes disengaged while the vehicle is operated in 4 high or 4 low and diagnosis indicates that replacement of the front axle actuator is necessary, use the following parts and instructions:

From start of production through Production

VIN # JE524063 Pontiac

JE535372 Fort Wayne Production

J1551431 Oshawa Production

Repair by replacing both the thermal actuator and the fork damper assembly.

Use: Actuator Assembly P/N 26013495

Fork Damper Assembly P/N 26013507

Production began using the fork damper assembly with the vehicle identification number breakpoints listed above. After these VIN's, repair with actuator assembly only.

Actuator Assembly P/N 26013495

The fork damper assembly reduces back pressure and the new actuator is a new part. Used together, these parts increase actuator life.

SERVICE PROCEDURE

Thermal Actuator Replacement

Remove and disconnect

1. Disconnect electrical wire from black junction located on axle tube.

2. Unscrew actuator (Figure No.1,i tem 16).

Install and connect

1. Install replacement actuator (Figure No.1, item 16). Tighten to 22 Nm (16 ft lbs).

2. Connect wire to black junction on axle tube.

Fork Damper Assembly Replacement

Raise truck and support using suitable safety stands.

Remove or disconnect

1. Actuator connector.

2. Indicator light connector.

3. Drive axle to tube bolts.

4. Axle mounting nuts.

5. Nut from the idler arm.

6. Nut from pitman arm.

Push the relay rod up and toward the front of the truck. Turn wheel out to loosen the drive shaft from the axle tube. Move axle shaft away from the axle tube and secure out of the way.

7. Stabilizer shaft link, if present.

8. Skid plate, if present.

9. Drain plug from the carrier and drain the axle lubricant.

10. Axle tube to carrier bolts.

11. Axle tube from carrier. Take care to keep the open end of the tube up.

12. Shift lever and fork. (Spring #13 in Figure No. 1 and clip #11 will not be in existing tube and are part of new fork damper assembly).

Install or connect

1. Shift lever, fork, spring and clip assembly into carrier case (Assembly P/N 26013507). Install spring (#10 in Figure No. 1) on shift lever. Clean mating surfaces of the axle tube and carrier assembly. Remove all oil and grease. Use carburetor cleaner or equivalent. Apply a bead of sealer (GM P/N 1052942, Loctite 518, or equivalent) to the tube sealing surface.

2. Axle tube to carrier.

3. Axle tube to carrier bolts and tighten to 40 Nm (30 ft lbs).

4. Drive shaft to axle shaft.

5. Drive shaft to axle shaft bolts and tighten to 80 Nm (59 ft lbs).

6. Axle mounting nuts with washers. Tighten to 80 Nm (59 ft lbs).

7. Relay rod to idler arm and pitman arm.

8. Idler arm washer and nut.

9. Pitman arm washer and nut. Tighten pitman arm and idler arm nuts to 54 Nm (40 ft lbs).

10. Stabilizer shaft link, if present.

11. Actuator connector.

12. Indicator connector.

13. Drain plug and the washer. Tighten plug to 32 Nm (24 ft lbs).

14. New lubricant. Refer to "Specifications" Manual X-8731, pg. 4C-6.

15. Filler plug. Tighten plug to 32 Nm (24 ft lbs).

16. Skid plate, if present.

17. Skid plate torx head screws. Tighten screws to 34 Nm (25 ft lbs).

Lower Truck.

For warranty replacement of the thermal actuator only use:

Labor Op. F0025 Time 0.3 hrs

For warranty replacement of the thermal actuator and fork damper assembly use:

Labor Op. T7525 Time 1.1 hrs

1. Shaft 22. Sleeve 41. Bearing 2. Deflector 23. Output Shaft 42. Seal 3. Seal 25. Plug 43. Deflector 4. Bearing 26. Washer 44. Flange 5. Tube 27. Pin 45. Washer 6. Bolt 28. Bolt 46. Nut 7. Thrust Washer 29. Carrier Case 48. Bushing 8. Retaining Ring 30. Bearing 51. Lock 9. Carrier Connector 31. Insert 52. Shaft 10. Spring 32. Sleeve 53. Thrust Washer 11. Clip 33. Side Bearing 54. Side Gear 12. Shift Fork 34. Bolt 55. Thrust Washer 13. Damper Spring 35. Differential Case 56. Differential 14. Shift Shaft 36. Pin Pinion Gear 15. Indicator Switch 37. Ring and Pinion 58. Bolt 16. Thermal Activator Gears 59. Shaft 20. Shim 38. Shim 60. Vent Plug 21. Differential Pilot 39. Bearing Bearing 40. Spacer

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.