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

Model and Year: 1988 C/K TRUCKS WITH HM 290 MANUAL TRANSMISSION

This bulletin is 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 C/K 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.

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.

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.

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.

B. Staking the bottom of the shift shaft socket roll pin hole will greatly increase the effort hrequired 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.

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

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.