M/T - Rattle/Clicking Noise in 2nd and/or 4th Gear
88chevy12REISSUE
Number: 88-148-7B
Section: 7B
Date: March, 1988
Subject: RATTLE/CLICKING NOISE
IN 2ND AND/OR 4TH GEAR
Model and Year:
1988 CK TRUCKS WITH HM 290 MANUAL TRANSMISSION
TO: ALL CHEVROLET DEALERS
This bulletin io being reissued to correct the part number listed for the Shift Shaft Socket. All Copies of 88-148-7B dated February, 1988 should be destroyed.
Some 1988 CK trucks with HM 290 4 or 5 speed manual transmissions may exhibit a rattle/klicking noise in 2nd and/or 4th gear. This condition may be caused by the shift shaft socket roll pin "walking" out of its bore and rubbing on the reverse speed gear in either of the two gear selections.
FIGURE 1 - HM-290 TRANSMISSION IDENTIFICATION INFORMATION RPO MCO/MG5:
Effective June 12, 1987, (Figure 1) all shift shaft sockets were staked on the bottom of the roll pin hole to retain the role pin and prevent it from "walking" out of its bore. Future intentions are to incorporate a stepped shift shaft socket roll pin bore, eliminating the necessity of staking.
To repair this condition, perform the following inspection and repair procedures:
1. Identify the customer comments that the rattle/clicking noise only occurs in 2nd and/or 4th gear.
FIGURE 2 - INSPECTING REVERSE SPEED GEAR AND ROLL PIN:
2. Remove the front housing and the shift shaft socket. Note the condition of the bottom of the roll pin and 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.
FIGURE 3 - STAKING SHIFT SOCKET ASSEMBLY:
3. 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, PART NUMBER 23049485. DO NOT REUSE A STAKED OR STEPPED BORE SHIFT SHAFT SOCKET. A used socket may NOT have enough material to retain the roll pin.
FIGURE 4 - SHIFT SHAFT PEENING:
B. Staking the bottom of the shift shaft socket roll pin hole will greatly increase the effort required to remove the roll pin for any additional 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.
FIGURE 5 - PROPER DEPTH OF ROLL PIN:
4. Reassemble the transmission using overhaul kit, part number 8672936 and make sure the shift shaft socket roll pin IS NOT installed below the surface of the shift shaft socket (Figure 5).
Overhaul procedures are covered in the 1988 Light Duty Truck Service Manual Section 7B1.
WARRANTY CLAIM INFORMATION
Transmission Assembly - Recondition K2700
C Truck 2.0 Hrs
K Truck 2.3 Hrs
Add Combinations
A - W/Skid Plate .3 Hrs
F - Replace Shift Rails and Fork Assembly 1.4 Hrs