M/T - Gear Rattle In Forward Gears/Shift Lever Rattle
88chevy23GMC NUMBER: 88-T-148
GROUP: 7B - Manual Transmission
DATE: August, 1988
CORPORATE
NUMBER: 877215
SUBJECT: GEAR RATTLE IN FORWARD GEARS/SHIFT LEVER RATTLE/BUZZ/VIBRATION OF SHIFT LEVER
MODELS: 1988C/K EQUIPPED WITH HM-290
FIGURE 1 - HM-290 TRANSMISSION IDENTIFICATION INFORMATION RPO MCO/MG5:
BULLETIN COVERS: (Figure No. 1)
1988 C/K Trucks equipped with a HM-290 4 or 5 speed manual transmission may experience gear rattle in any or all forward gears, or a condition of shift lever rattle/buzz and/or excessive vibration of the shift lever. (Some movement of the shift lever is normal, especially with the 4.3L engine, unless it causes a rattle noise.) Any of the above conditions could be caused by excessive clearance in the shift lever housing assembly transmitting vibration and rattle to the driver compartment. The condition(s) will increase with engine RPM and be in any or all gears, including neutral. The gear rattle, shift lever rattle/buzz and excess vibration of the shifter can be repaired by installing a new shift lever housing assembly. The new shift lever housing assembly uses compression grommets at the pivot points, eliminating the chance of excess clearances due to improper shim selection.
IMPORTANT: A slight gear rattle at low engine RPM (800-1200 RPM) is normal to all manual transmissions. The service repair described above will only reduce the rattle condition due to improper shimming.
FIGURE 2 - SHIFT LEVER HOUSING ASSEMBLY:
DATE OF PRODUCTION CHANGE: (Figures No. 1 and No. 2)
Beginning May 20, 1988 all HM-290 transmissions are built with a new shift lever housing assembly that requires no shims. This new part uses an updated material for the boot and inside lever seal so no O-rings (129) and (131) are required to prevent leakage.
NOTE: There was an interim change January 5, 1988 to May 20, 1988 where the updated boot and inside seal material were used (on the previous part with shims) so no Orings were required.
SERVICE ACTION:
To repair this condition, replace the shift lever housing assembly with the parts listed under Service Parts Information.
SERVICE PARTS INFORMATION:
Part No. Description
23049538 Housing Assembly, Shift Lever
(RPO MCO) (4-speed)
08672191 Housing Assembly, Shift Lever
(RPO MG5) (5-speed)
23049572 Seal (service only)
SERVICE MANUAL REFERENCE:
Refer to the On-Vehicle Service Section 7B of the 1988 C/K Pick-Up Truck Service Manual for service procedures.
LABOR TIME INFORMATION:
For repairs to vehicles under warranty, Use K1120: Control Assembly, Floor Mounted Gearshift - R & R or Replace
Labor Time: 0.7 Hr.
SERVICE NOTES:
The HM-290 overhaul video shows the axial clearance measurement of the shift lever housing that requires shims. This checking procedure is not for the new shift lever housing that uses the compression grommets instead of shims.