M/T - Noise, Rattle, Clicking In 2nd/4th Gear
88chevy03
GMC NUMBER: 88-T-77
GROUP: 7B - Manual Transmission
DATE: January, 1988
CORPORATE
NUMBER: 877207
SUBJECT: NOISE/RATTLE/CLICKING IN 2ND AND/OR 4TH GEAR
MODELS: 1988 C/K MODELS EQUIPPED 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 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).
FIGURE 1 - HM-290 TRANSMISSION IDENTIFICATION INFORMATION RPO MCO/MG5:
DATE OF PRODUCTION CHANGE: (Figure No. 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.
FIGURE 2 - INSPECTING REVERSE SPEED GEAR AND ROLL PIN:
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 No. 2). If the roll pin and reverse speed gear show signs of rubbing, perform the following procedure.
FIGURE 3 - STAKING SHIFT SOCKET ASSEMBLY:
1. Stake the bottom of the shift shaft socket roll pin hole in two places with a punch (Figure No. 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.
FIGURE 4 - SHIFT SHAFT PEENING:
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 No. 4). If "peening" is encountered, replace the shift shaft and the rear housing shift shaft bearing.
FIGURE 5 - PROPER DEPTH OF ROLL PIN:
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 No. 5)
SERVICE PARTS INFORMATION
Package No. Qty. Package Description
1052931 2 Manual Transmission Fluid
(1 Qt.) .946L
8672936 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.
LABOR TIME INFORMATION:
Use K2700: Transmission Assembly - Recondition C-Truck . . . . . . 2.0 Hrs. K-Truck . . . . . . 2.2 Hrs.
ADD: A-W/Skid Plate (If K-Truck is equipped with one)................................. . 0.3 Hr.
ADD: F-Replace Shift Rails and Fork Assembly.. .......................... 1.3 Hrs.