Here is information on this problem it looks like the transfer case actuator is to blame in most cases:
SLOW/NO ENGAGEMENT OF FRONT AXLE WHEN 4WD SELECTED
File In Section: 4 Drive Axle
Bulletin No: 76-43-01A
Date: September 1998
Slow or no Engagement of Front Axle when 4WD is selected (Replace Front Axle Actuator)
1988-97 Chevrolet and GMC K Models
excluding 1988-93 Models over 8500 # GVW
This bulletin is being revised to add information to the Service Procedure, add a new part number, and include schematics. Please discard Corporate Bulletin Number 76-43-01 (Section 4 - Drive Axle).
Some owners may comment that the colder the outside temperature is, the longer it takes for the front axle to engage when 4 wheel drive is selected, or the front axle does not engage.
The front axle engagement actuator is a thermally activated component. Because of this characteristic, the time required for the actuator to complete 4 wheel drive engagement is extended as the temperature drops.
Replace the front axle actuator and include the applicable wiring harness kit. Refer to the Parts Information in order to determine which wiring harness kit is needed.
1996 model trucks with a build date on or after January 2, 1996 are considered as "961". If the build date of the truck is unknown, verify the 3 character "axle code" on the front axle label in order to determine which wire harness to order.
This new actuator uses a motor to engage the front axle and is not affected by temperature. On 1988-93 models with a GVW rating over 8500$, the new actuator cannot be installed and the thermal actuator will remain the service part.
P/N Description Qty 26060073 Actuator Asm, Frt Drive Axle 1 22510339 Fastener 1 15313272 Harness, Jumper (Z Splice) 1 (86-93 K1-3)
Parts are currently available from GMSPO.
Some owners with actuators that are operating as designed (5-30 seconds engagement time) may choose to upgrade to the fast actuator at their own expense. The fast actuator is a new product enhancement and should not be used to replace actuators that are operating as designed.
Check out the images (below). Please let us know what you find. We are interested to see what it is.
Saturday, December 24th, 2022 AT 11:08 AM