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

Model and Year: 1988 C/K TRUCKS WITH HM 290 MANUAL TRANSMISSION, (RPO MCO, MG5)

This bulletin is being reissued to correct the part number listed for the manual transmission fluid. All copies of 88-143-7B dated February 1988 should be discarded.

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 1) .

Starting November 13, 1987 (Figure 2) 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 PARTS INFORMATION:

Package No. Package Description

1052931 (2) Manual Transmission Fluid (1 Qt). .946L 8672936 (1) HM 290 Overhaul Kit 8672050 (2) Synchronizer Rings (2) 8672927 (1) 2-4 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.

LABOR TIME INFORMATION:

Labor Operation: K2700 Labor Time: C Truck 2.0 K Truck 2.3

ADD: A w/shield plate .3 (K Truck)

I Recondition Mainshaft 2.0 (4 sp/ 5 sp)

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.