If it doesn't have manually locking hubs on the front wheels, It means it's a "constantly" locked front 4x4. You don't have to lock them, they already are.
unlock your front hubs
ok it should have lock in hubs so pull your 4x4 switch onto 4x4 high and get out and turn your hubs on both sides on your front wheels
Drives the front wheels.
When u find out why then let me know cause my 97 does the same thing.
If the back wheels slip / spin it automatically will transfer some of the power to the front wheels
If by lock up you mean squeal when cornering, such as in a parking lot, this is because the grand Cherokee (4x4) is commonly an all-time 4-wheel drive. You can determine this by looking at the 4X4 shifter and it should say quadra-trac. When cornering, the wheels spin at different speeds which causes the computer to think it's losing traction, then engages 4X4 and locks up the front end. Thus, causing it to "bark" or "squeal". Hope this helps, -Dayne
Manually turn front free wheeling hubs to lock (front wheels) Place $wd gear stick to 4H or 4L - $wd light will come on on dash
check that the lock that locks your front tyres into 4x4 still works and if your 4x4 is activated by switch get your electrics checked
If your transfer case doesn't have a power divider lock, then the torque from the gear rotation will follow the path of least resistance - which, in this case, would be the front shaft, which will have significantly less resistance.
what year The older Broncos Have a lever in the middle of the floor board up front. Just pull the lever back to go into 4Hi, back more for Neutral, and then again for 4Lo. The newer models had a button on the dash that you push to put it in 4x4. If you do not have automatic locking hubs on the front wheels you'll have to get out and manually lock them to engage the front wheels with the front axles...otherwise the trasfer case will just spin but no power will be conveyed to the front wheels. Locking the hubs is quick and easy. Just turn the knob a quarter turn in the direction that says "LOCK". Be sure you don't drive on pavement at speeds over 35 mph with the 4x4 engaged and the hubs locked. Turning sharply on pavements or driving at high speeds with 4x4 engaged can damage the transfer case and/or front suspension components.
There aren't any lock outs at the hubs. There is a vacuum actuated shift hosing on the front axle.
A 2003 Ford Explorer is REAR wheel drive ( and if it has the Control-Trac 4x4 system , and it is set on 4x4 AUTO , if the back wheels were to " slip " then some of the power is transferred to the front wheels )