HIGH TRANSFER CASE SHIFT EFFORT - REPAIR PROCEDURE

Subject: HIGH TRANSFER CASE SHIFT EFFORT

Model and Year: 1983-91 Tl TRUCKS 1988-91 K TRUCKS

TO: ALL CHEVROLET DEALERS

THIS BULLETIN CANCELS AND SUPERSEDES DEALER SERVICE BULLETIN NO. 91-128-7A, DATED NOVEMBER 1990. THE BULLETIN NUMBER HAS BEEN CORRECTED IN THE FIRST PARAGRAPH. ALL COPIES OF 91-128-7A SHOULD BE DISCARDED.

Some four wheel drive K and T trucks may experience high transfer case shift effort and/ or total blockouts when "SHIFTING ON THE FLY" from 2H to 4H under cold weather conditions (usually 25 degrees or less). In order to shift to 4H the speed of the front propshaft must be increased to allow proper engagement of front axles. As the transfer case shift lever is moved into 4H the front propshaft begins rotating to synchronize the front axle assembly. In cold weather conditions regular production lube has high viscosity which may delay or prohibit the synchronizing of the front propshaft and axle resulting in high transfer case shift effort.

To reduce high shift effort, regular production front axle gear lube may be replaced with a 75W-90 synthetic gear lube which maintains a lower viscosity under cold weather conditions. This synthetic gear lube is now available in one quart containers from GMSPO. Before installing, it is important to drain and flush the front axle with clean mineral based (non synthetic) axle lube. The front axle should then be refilled to the level of the filler hole with synthetic lube listed below.

Front Axle Lube Capacities: K1, K2 - 1.66 liter (1.75 qts) K3 - 2.13 Liter (2.2 qts) T1 - 1.20 liter (1.3 qts)

SERVICE PARTS INFORMATION

P/N DESCRIPTION --- ------------------------------- 12345836 SAE 75W-90 synthetic gear lube, 1 qt. bottle

Parts are currently available from GMSPO.

WARRANTY INFORMATION

For vehicles repaired under warranty use:

Labor Operation Number: T7980

Labor Time: .4 hr

Trouble Code: 92

NOTE: Labor Operation is coded to base vehicle coverage in the warranty system.

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.