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

TRANSMISSION APPLICATIONS: SUBJECT: ------------------------- ------- 1988 HM-290 MANUAL NO 4TH GEAR OR HARD SHIFT INTO 4TH TRANSMISSION (RPO MCO, MG5)

TRANSMISSION MODELS: VEHICLE APPLICATIONS: ------------------- -------------------- ALL MODELS 1988 C/K TRUCKS

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 2).

DATE OF PRODUCTION CHANGE: (Figure 1) -------------------------- Starting November 13, 1987 new "wing" design synchronizer keys that prevents 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. Package Description ----------- ------------------- 00993204 (2) Manual Transmission Fluid (1 Qt.) .946L 08672936 (1) HM-290 Overhaul Kit 08672050 (2) Synchronizer Rings (2) 08672927 (1) 3-4 Hub Selective Snap Ring Set (6) 23049729 (1) Synchronizer Assembly, 3-4 (7) - (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 7B1 of the 1988 Light Duty Truck Unit Repair Manual or procedures.

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.