Transfer Case - Increased Shift Effort From 2H to 4H: Overview

91chevy22

Number: 91-404-7A

Section: 7A

Date: AUGUST 1991

Corporate Bulletin No.: 167401

ASE No.: A2


Subject: HIGH TRANSFER CASK SHIFT EFFORT


Model and Year: 1988-91 T1 TRUCKS


Some 1988-91 T-Trucks may experience high transfer case shift effort or total blockouts when "shifting on the fly" from 2H to 4H under cold weather conditions.

This condition may be corrected by the installation of the synthetic 75W90 gear lube described in Dealer Service Bulletin No. 91-128-7A. This fluid maintains a more constant viscosity under cold weather conditions allowing quicker front axle synchronization and easier transfer case engagement.

If the installation of the synthetic fluid does not result in a satisfactory shift effort, an "Easy Shift" package may be installed in the transfer case. This package features a roller pin (53) rather than a solid pin on the mode shift fork (54) and revised ramp angles on the sector (55) to reduce engagement forces. This package was installed in the 1991 model year and will provide reduced transfer case shift effort under cold weather conditions.

Figure 1:

VEHICLES INVOLVED:

Group A:

Some 1988-91 T-Trucks equipped with transfer cases identified by the following part numbers:

15568078 15627441
15568079 15627442
15568597 15653450

This part number can be found on the identification tag (80) located on the rear case half (Figure 1).

Group B:

Some 1991 T-Trucks equipped with transfer cases identified by the following part numbers and built before 10/22/90:

15653414 15659232

This part number and build number can be found on the identification tag (80) located on the rear case half (Figure 1).