I have a 2003 ford f150 automatic 6 cyl 4x4 with a manual 4 wheel drive shift and auto locking hubs. when I put it in 4 wheel drive the hubs wont engage till I drive the vehicle for around 5 miles then they engage. Anyone know what cause this, cause I dont know where to start.

 

It could be a small vacuum leak, the front hubs are vacuum operated.

I would check the vacuum lines from the solenoids on the passenger side firewall to the vacuum actuator on the front diff. You have to check very carefully because even the smallest of cracks can cause a problem. I would also check the solenoids and vacuum actuator themselves for cracks and stuff.

 

what is the best way to check the vacuum lines, also after reading other post it sounds like when vacuum is applied to the actuater that what disengages the hubs could i unplug the vacuum lines and then check the hubs to see if they are engaged?

 

The vacuum actuator motor is a duel diaphragm design. Vacuum pulls the actuator rod both ways. When 4x4 is engaged vacuum is vented on one side and applied to the other side. This moves the rod in the desired direction. If you have access to a vacuum pump with a gage apply vacuum to test the lines for leaks. Disconnect both lines at the solenoids and apply vacuum to the lines one at a time. I ended up replacing my lines with rubber hose. The solenoids allow vacuum to pass through or vent it to atmosphere. When they are activated they allow vacuum to pass from the bottom nipple to the top and down to the vacuum actuator motor. When they are deactivated they close off the bottom nipple and vent the top nipple to atmosphere to remove vacuum from the actuator motor. The solenoid closest to the engine disengages the front axle and the one closest to the passenger side fender engages the front axle. There are two wires each going to the solenoids. Two of them will be the same colour. These two supply 12 volts to the solenoids. The other two are grounded by the GEM to activate the solenoids. Check the two similar coloured wires for 12 volts. There are vacuum reservoirs behind the battery box. They store vacuum from the engine and supply it to the solenoids. One of the reservoirs is for the heating and A/C controls ant the bottom one is for the solenoids. Check them both for cracks/leaks. There are 2 check valves in the lines coming from the engine. They keep vacuum from venting back out of the reservoirs when the engine is turned off.

.