RATTLE OR CLICK NOISE IN 2ND GEAR OR 4TH GEAR M/T

TRANSMISSION APPLICATIONS: SUBJECT: ------------------------- ------- 1988 HM-290 MANUAL NOISE/RATTLE/CLICKING IN 2ND AND/OR TRANSMISSION (RPO MCO, MG5) 4TH GEAR

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 noise/rattle in 2nd and/or 4th gear. The noise/rattle may also sound like a clicking noise. This condition may be caused by the roll pin that holds the shift shaft socket to the shift shaft "walking" down and rubbing on the reverse speed gear that is on the mainshaft (when the shift shaft socket is in the 2nd and/or 4th position). To repair this condition, perform the following inspection and repair procedure:

DATE OF PRODUCTION CHANGE: (Figure 1) -------------------------- Starting June 12, 1987 all shift shaft sockets are staked on the bottom of the roll pin hole so the roll pin will not "walk" down and rub on the reverse speed gear. At a later date, all HM-290 models will be built with a shift shaft socket that will have a "stepped" roll pin hole, eliminating the need for staking.

SERVICE ACTION:

Remove the front housing and the shift shaft socket. Note the condition of the bottom of the roll pin and the top edges of the reverse speed gear teeth (Figure 2). If the roll pin and reverse speed gear show signs of rubbing, perform the following procedure.

1. Stake the bottom of the shift shaft socket roll pin hole in two places with a punch (Figure 3).

IMPORTANT: ---------- A. If there is evidence of prior staking, USE A NEW SHIFT SHAFT SOCKET. DO NOT REUSE A STAKED OR STEPPED SHIFT SHAFT SOCKET. A used socket may not have enough material to retain the roll pin.

IMPORTANT: ---------- B. Staking the bottom of the shift shaft socket roll pin hole will greatly increase the effort required to remove the roll pin for other transmission work. This increased effort may cause the rear housing shift shaft bearing to "peen" the shift shaft during removal of the roll pin, causing a "gritty" shift feel into or out of gear (Figure 4). If "peening" is encountered, replace the shift shaft and the rear housing shift shaft bearing.

2. Reassemble the transmission and make sure that the shift socket roll pin IS NOT installed below the surface of the shift shaft socket. (Figure 1)

SERVICE PARTS INFORMATION:

Package No. Package Description ----------- ------------------- 00993204 (2) Manual Transmission Fluid (1 Qt.) .946L 08672936 (1) HM-290 Overhaul Kit 23049485 (1) Socket Asm-Shift Shaft (123)

SERVICE MANUAL REFERENCE:

Refer to Section 7B1 of the 1988 Light Duty Truck Unit Repair Manual for 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.