HIGH SHIFT EFFORT TRANSFER CASE

SUBJECT: HIGH TRANSFER CASE SHIFT EFFORT

MODELS: 1988-90 Kl,K2,K3 AND 1983-91 Tl LIGHT DUTY TRUCKS

THIS BULLETIN CANCELES AND REPLACES GMC TRUCK SERVICE BULLETIN 89-T-90 DATED AUGUST 1989 TO ADD 1990 K MODELS AND 1983-91 T MODELS AND TO REFLECT THE AVAILABILITY OF SYNTHETIC 75W-90 GEAR LUBE IN ONE QUART BOTTLES FROM GMSPO.

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 axle. As the transfer case shift lever is moved into 4H the front prop-shaft 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 viscos- ity 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.

Front Axle Lube Capacities: Kl, K2 - 1.66 liter (1.75 qts) K3 - 2.13 Liter (2.2 qts) Tl - 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: T7980 Labor Time: .4 hr

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.