I have had 2 4-wheel drive in the past 45 years. You go to 4-W low at almost stop position and 4-W high at a low range. If you are shifting on the go you are tearing up yourTransmission up.
If you are driving in 4H on hard surfaces and just flip the switch to 2H still on the hard surfaces it will react exactly as you describe
when in 4H as there is no internal diff action in the transfer case , a condition known as torque wind up occurs and places heavy loads on the drive line components thereby locking the gear teeth and that will not allow the separation on selecting 2W drive
if at some point one wheel looses traction for a split section, that torque wind up is reduced and the pressure on the actuator slams the selector out of engagement
4H should only be used in slippery conditions , mud, dirt ,snow,ice, grass etc where the wheels loose traction and allow that wind up to dissipate
if you continue to drive on hard surfaces in 4 H then transmission failure will occur earlier than can be expected
SOURCE: 99 silverado 4wd went out... transfer case?
a little tip a friend gave me in unlocking the 4wd drive on ramps or hill and then put in neutral let roll back a foot put in park and then let off the 4wd
when in 4wd the hubs get a little heated cause they need greased so they stick into position making it hard to come out of 4wd this which i spoke of i got stuck in the senerio where i almost drove home in 4wd from 300 miles away but i called my friend he told me bought this and so i thought it could help you
your hubs just locked up on you your bearings are going to need to be packed again this is normal for this
hub
SOURCE: 1988 chevy 4x4 actuator
The switch for the 4wd light is on top of the transfer case. It is probably sticking
SOURCE: 01 Chevy Silverado 4 X 4 not working. 4WD light
Having the same exact problem but with my 1999 escalade. Thought it was the actuator bought a new one installed it transfer case would engage but front end wouldnt lock. Took it out of housing left it plugged in got a friend to go through all the 4wd for me and the plunger never moved out the actuator. Checked my wiring harness which is a four prong ann it had one hot prong like it is suppose to. Traced wires even replaced dash switch same problem. Taking it to local dealership tom to have it checked for codes. I was told it could be the transfercase actuator even though its workin that actuator is what sends power to the front to engage the actuator to lock the differential.
SOURCE: I have a 2002 Chevy
Fuse is located at the end of eh dash on drivers side and the Actuator is located at the front differential and on the passenger side.
When in 4wd mode, a switch on top of the transfer case conducts 12 volts out to the actuator. Wire #50 (brown) is the 12v feed, and it conducts to the light blue wire (#900) to the actuator.
When shifted out of 4wd, the switch opens up and no voltage goes to the actuator.
Check voltage at the connector for the front actuator (at the front differential - it looks like a large bullet that threads into the front diff.) If it has 12 volts, the actuator is the problem. If it does not have 12 volts, check the transfer case switch and the power feed to the transfer case.
I'll assume it is the actuator, if the plug to the actuator is getting 12 volts when in 4wd.
The way this actuator works, is it is a sealed chamber that gets heated by voltage. When it heats, the pin in the end swells and pushes a shift fork in the front differential. The shift fork engages a spline on the passenger side of the differential, and boom! you have 4WD.
GM offered an upgrade to this actuator that is a motor instead of a heated device. However, it requires a small harness addition, a spacer, and a new actuator. It is about a $150 to $200 option.
Good luck. The actuator is usually the problem 90% of time but recheck all of the wire harness just to maker sure there is no short before replacing any parts. The actuator may not be fully engaged or disengaged and the fork to the spline may be what is causing the grinding.
88-UP C/K ACTUATOR UPGRADE
VEHICLE SERVICED: 88-99 CHEVROLET FULL SIZE
PURPOSE: IMPROVE AXLE CONNECT ENGAGEMENT TIME AND
COMPONENT RELIABILITY.
SYMPTOMS: NO FRONT DRIVE AXLE ENGAGEMENT WHEN SHIFTED INTO 4X4.
Obtain the following GM part numbers:
(1) 26060073 Actuator
(1) 88959465 Harness/Spacer Kit
SOURCE: 4x4 quit working
Jack up the rear wheels and put it on jack stands. Have someone get in it and put it in 4wd and drive. Release the brake. Rear wheels are spinning only right. Don't get under it but look under it and see if the front driveshaft is spinning. If the shaft is spinning but the wheels aren't it is likely a bad front axle actuator. If the front shaft isn't spinning it is a transfercase problem.
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