Installed new 4wd actuator in 2002 F-150, hooked up vacuum lines, but 4x4 light does not come on and 4wd does not engage. Is there a little bit of time for vacuum to build, or did I do something wrong. Seems like there is only one way to do it. It is a manual 4wd, or stick for shifting from 2H to 4wd

check the vacuum lines for cracks bend them a little when doing so to expose any hidden cracks make sure the end is on good.

When you put the controls in 4lo, the transfer case will engage, but that doesn't mean it is in4wd. The 4wd function is controlled mainly by vacuum lines. So check every vacuum line you can see. On earlier models there was a large diameter vacuum hose that went to a vacuum operated actuator hidden under the battery. It controls the switch that engages the front axle. You'l have to remove the battery and battery tray to see it. Check that hose to see if it has come loose. 90% of s10 and gmc 4wd problems can be traced back to that hose. If it is loose, you will probably have to replace it with a new hose. The old hose gets brittle and won't stay hooked up.

There is a vacuum line that goes to the transfer case.if this line is ruptured it will not engage the 4wd.Next there is a switch on the t-case that may not be working.In 4wd it supllies vacuum to the 4wd actuator that is under the battery tray.next the applied vacuum pulls the cable engaging the frontaxle.

the vacuum hoses or wheel seals are leaking in the front wheels. they are vacuum operated. the dealer has kits you can buy to convert to manuel locking hubs, they had alot of problems with the vacuum hubs

Check first to see if the front drive shaft is turning when you put it into 4wd. If it is the problem lies either in the front differential or the vacuum leading to the actuator. Find the vacuum line coming from under the battery compartment and follow it to the actuator solenoid mounted on the firewall. Disconnect the two and connect them together with duct tape. If your 4wd engages it's probably the actuator solenoid. About a $59.00 fix.

On the full size, the front actuator is electric, not vacuum.

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.

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 whining or grinding noise you hear.

88-UP C/K ACTUATOR UPGRADE
VEHICLE SERVICED: 1994 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

Any time your dealing with a 4x4 system the best start is at you front axle. Its primarily a vacuum leak so check to see if the 2 vac lines are hooked up (its good to check the electric connections.). When your 4 wheel drive is engaged and the motors running you should have vacuum at one or both of thee lines depending on if your in 4 hi or low .
If no vacuum at axle check the Vacum switchs(the plug with 4 vac lines) on top of the transfer case it will have 2 feed lines(grey & green) they conect in to the into the vacum harness on back of motor (passanger side). A vacum schematic is normally located on the raditor core support (right under the hood next to hood release)
Hope this helps

I own a 98 short box S10 4X4 with a Vortec 4.3 and a posi rearend. I have had to check all these areas of the 4wd system. Could be one of the following or a combo of more than one __1. the fuses 2. the actuator (under the battery tray) 3. the cable from the actuator to the front differential 4. the transfer case control module (behind passenger side kick panel) 5. the vacuum switch (on top of the transfer case) 6. the push button on the dash.7. cracked or dry rotted vacuum lines in the system. Any of these not working properly will prevent you from getting your truck into 4wd. My issue ended up being the cable and the actuator. I had a vacuum issue which would not let the actuator pull the cable to engage the front axles.Replaced the vacuum lines and the vacuum switch and still no 4wd.Turned out to be the actuator and the actuator cable. Fixed that and now I have 4wd any time I want. If you hear a clicking sound at the transfer case,its fine. If you hear another click at the TCCM, its fine. If all your lights work on the dash switch, its fine. If your actuator doesn't leak any air, its fine. I replaced the vacuum switch for $15 at advanced auto parts. Turned out I didn't need it. I don't drive my truck unless there is a lot of snow so I just locked the front differential until I get a new actuator $30 and actuator cable $30. This was how I fixed my problem and I hope this info can help others,

If you engage the 4WD with a switch instead of manually, there is a motor in or on the transfer case. Because of the location, these can go bad. u need to check all your switches and actuators there are actuators under vehicle that clog up with dirt.also try putting vehicle in neutral before engaging 4x4.
This will help. Thanks please keep updated.please do rate the solution positively .thank you for using fixya.

sounds like it is loosing vacuum check all the lines for a crack even the engine lines will cause it to loose vacc. pressure. if it is not run to the vacuum reserve canister you may not have enough vacc. to hold the actuator in several times I just run new lines and that helped and not very costly.