electrical..the use an actuator in the front diff to physically lock it up..look under the front diff and tell me if #8 in this picture is black or its aluminum..then you need to remove that actuator then turn key on and shift inot 4WD and see if the actuator pushes out so when its in the front diff it will push and lock up the front diff for 4WD..you understand what we need to do?
Technical Service BulletinFile In Section: 4 Drive AxleBulletin No.: 76-43-01ADate: September, 1998Subject:Slow or no Engagement of Front Axle when 4WD is selected (Replace Front Axle Actuator)Models:1988-97 Chevrolet and GMC K Modelsexcluding 1988-93 Models over 8500 # XXXXXThis 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 (SectionXXXXXAxle).ConditionSome owners may comment that the colder the outside temperature is, the longer it takes for the front axle to engage whenXXXXXis selected, or the front axle does not engage.CauseThe front axle engagement actuator is a thermally activated component. Because of this characteristic, the time required for the actuator to completeXXXXXengagement is extended as the temperature drops.CorrectionReplace 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.
Parts are currently available from GMSPO.
If binding occurs before the actuator is seated, remove the actuator and reseat the spacer by pushing on the spacer with a screwdriver. Then reinstall the actuator.On K3 Models with the cast iron axle tube, there may be a casting burr which may contact the edge of the actuator. This should not create a concern and the actuator should seat against the axle tube. If this contact remains a concern, use a die grinder in order to remove the burr.
The new Fast Axle Actuator requires only 1 splice.
Connections must be water tight in order to prevent water from entering the circuit and causing damage to the components.
This relay incorporates a 5 second delay for the front axle to engage in order to allow the transfer case synchronizer to energize.For 88-93 vehicles, if the axle has to be replaced, use jumper harness P/N 15313272. CKT 1695 (BLK/WHT) fits into cavity A of the fast actuator. The circuit includes the cable seal and the terminal pin. This circuit plugs into the 5-pin axle actuator connector.