First time poster. I recently purchased a 2002 F-250 4x4 XLT with the v10. I'm working on the usual little niggles you get with a used car. The 4x4 system doesn't engage when the dash switch is selected. You can hear the drive shaft engage, but the hubs are not engaging. I read various posts, and did the following.

1. Checked to see if the defrost engages when 4x4 is selected (Does not)
2. Checked vacuum lines to either wheel (one was disconnected completely, and the other had vacuum)
3. Verified the vacuum reservoir held vacuum (it does)
4. I started pulling connections to see if the loss could be found, and the vacuum relay has two lines (red/black) Red held vacuum, but black did not.

Is this a vacuum switch relay issue? I am going to replace the vacuum lines as they look well worn, but it appears only one hub is getting vacuum. I'm all ears and thanks for the forum!

jeff

 

With everything connected, disconnect the "T" after the vacuum solenoid, and put a vacuum gauge on it.

Cycle the 4x4 switch from 4x2 to 4x4HI, wait a minute, then go back.

Was there around 45 seconds of vacuum at the "T" when the switch is first cycled from 4x2 to 4x4HI? Was there a shorter pulse of vacuum when turning the switch back to 4x2?

If yes to both questions, using a vacuum pump, check that the hubs hold vacuum. If they do, reconnect everything, and with the front wheels jacked up off the ground, turn the switch from 4x2 to 4x4HI and wait a minute. Check if the hubs engaged to the axle by spinning the wheel and making sure the axle turns with the wheel.

Sometimes, the vacuum will hold the hub engaged for the 45 seconds or so, and then when the vacuum goes away, the hub will release. This is what one of mine was doing, as it bad broken the latch inside the hub.

I replaced them with Warns and haven't looked back.

Do the above diagnosis and report back.

 

Krewat thank you. I found my right hub held vacuum, but not the left. I also think you're absolutely right in swapping out the factory hubs for Warn or Mile Marker. My only question is how/where to cap the vacuum lines to the hubs? Is the barbed fitting on the wheel threaded, and can I thread in a plug to prevent any debris from getting somewhere it shouldn't? Thanks!

jeff

 

The barb on the knuckle is a regular pipe-thread, maybe 1/8"?

You could, if the hubs can be manually locked, leave them as-is, and just lock them by hand. That is, if they even move at this point