NO 4TH OR HARD SHIFT TO 4TH GEAR (NEW DESIGN SYNCHRONIZER)

MODELS: 1988 C/K MODELS, EOUIPPED WITH HM-290 4-SPEED (RPO MCO) OR 5-SPEED (RPO MG5) MANUAL TRANSMISSIONS

BULLETIN COVERS:

Some 1988 C/K trucks equipped with a HM- 290 4 or 5-speed manual transmission may exhibit a no 4th gear or hard shift into 4th gear (4TH GEAR ONLY). This condition may be caused by a key cocking in the 3-4 synchronizer assembly. To correct the condition, install the service parts package that contains new "wing" design synchronizer keys (Figure No. 1).

DATE OF PRODUCTION CHANGE: (Figure No.2) ------------------------- Starting November 13, 1987 new "wing" design synchronizer keys that prevent cocking are used in only the 3-4 synchronizer assembly. At a later date, the new keys will be used in the 1-2 and the 5th-Reverse synchronizer assemblies.

SERVICE ACTION:

Install the service part packages listed below.

SERVICE PARTS INFORMATION:

Package No. Qty. Package Description ---------- --- ------------------- 1052931 2 Manual Transmission Fluid (1 Qt.) .946L 8672936 1 HM-290 Overhaul Kit 8672050 2 Synchronizer Rings (2) 8672927 1 3-4 Hub Selective Snap Ring Set (6) 23049729 1 Synchronizer Assembly, 3-4 (7) Includes: 1 Synchronizer Sleeve (8) 3 Synchronizer Detent Ball (9) 3 Synchronizer Detent Spring (10) 3 Synchronizer Key, ("wing" design) (11) 1 Synchronizer Hub (12)

NOTE: Inspect the 3-4 synchronizer assembly prior to installation to make sure that it was built with the new "wing" design synchronizer keys.

SERVICE MANUAL REFERENCE:

Refer to section 7Bl of the 1988 Light Duty Truck Unit Repair Manual for procedures.

LABOR TIME INFORMATION:

Use K2700: Transmission Assembly -

Recondition C-Truck ....................2.OHrs. K-Truck...... ............2.2Hrs. ADD: A-W/Skid Plate (If K-Truck is equipped w th one) ... ..... ............. 0.3 H r. ADD: I-Reconditioned Mainshaft (4sp/5sp) . . . . .. . . 1.7 Hrs.

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.