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Re: 4x4 not working when i shift it in 4x4 auto trans
Find the accuator on the front axle it has a two wire pigtail and threads into the axle housing. Check for power and ground if you have both when the transfer case is in 4x4 the replace the accuator. They are available at most parts stores and are a very common problem. Let me know how it goes.
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ARE THE HUBS LOCKED IN FIRST? FOR YOU HAVE TO LOCK AND UNLOCK THOSE HUBS FROM THE OUTSIDE.. EACH TIME YOU GO INTO 4X4 AND WHEN YOU GO OUT OF 4X4 TO 2 WHEEL..DRIVE. OR YOU DON'T HAVE A FRONT DRIVE SHAFT GOING TO THE FRONT AXLE?? OR ITS BROKEN OR THE TRANSFER CASE IS BAD??
The 4x4 system on an 88-98 full size gmtruck is controlled electronically except the shifting of thetransfer case which is done with a lever. When the transfer case isshifted into a 4x4 gear a switch in the upper driver side of thetransfer case is closed this sends power to the front axle actuatorwhich engages the front wheels to the front axle. A sensor is alsolocated on the front axle which is closed when the actuator shiftsthe axle into gear.
The first thing to check is the 4x4fuse if it is bad replace it. Next check the switch on the transfercase connect a continuity tester to the switch and shift the transfercase into 4x4 the stitch should close, if it dose not replace it ifthe switch is functioning properly replace actuator on front axle
Lift and support the front of the truck so the front wheels are off the ground ( take safety precautions, chock wheels, jack stands, etc ). Key on, engage 4x4 and try to turn the front drive shaft. If it turns it is a problem with the transfer case. If it doesn't it is a front axle engagement problem. I would guess a problem with the vacuum disconnect motor on the front axle ( or vacuum lines from teh solenoids or the solenoids themselves ), but best to verify the test above to know which way to go. Post back a comment after the test.
This is for 4x4 shifter on the floor.
In the front of the truck on the axle there's a plastic cover with 2 10mm bolts remove it and spray down the shifting actuator it operates on vacuum. You might have to pull it in four wheel and check to see if the vacuum pod is engaging the shift lever on the axle. Then again you might have to replace it very easy to do. But I would spray it down with some WD-40 it should work.
shift into 4wd and move truck a couple of feet.
if light is still off, park truck block the wheels set the park brake jack right front wheel and try to hand spin the wheel if wheel doesn't turn 4x4 is functioning properly but there is a wiring problem use an ohmmeter to check the 4x4 switch wiring fuse and bulb
if wheel turns freely the front axle or transfer case is not engaged
attempt to hand spin the front driveshft if the driveshaft will spin the transfer case is not engaged check the transfer case shift linkage, problem is in linkage or transfer case internals
if the driveshaft will not spin the transfer case is engaged properly
with trnsmission in neutral or park start engine measure vacuum on the two vac lines at front axle shift motor . one line should have approx 20" vacuum. other line should have none
if no vacuum measured look for vac leak or bad vac switch
if both lines have vac look for a bad vac swithc or ruptured cad actuator diaphragm
if one line has 20" +- VAC
move transfer case lever to 2wd measure vac again lines should have swapped vac signals
if no vac switch bad or 4wd shift likage needs adjusting
if yes vac motor bad or stuck or shift fork stuck
remove vac shift motor from the axle attach vac lines to shift motor engage disengage 4wd
does shift motor plunger move at least 1/2 inch
no shift motor bad
yes check axle shift fork and vac motor for binging