Superduty “4×4 not engaging” problems? This is a very common issue, here is how to fix it. It might be a quick patch/replacement of a vacuum line, or a solenoid replacement. I made a quick video that will only take a couple minutes for you to figure out what the problem is, and depending on the problem, the actual fix shouldn’t take you more than 15 minutes. When I had this problem I couldn’t find a good resource to troubleshoot, so hopefully this helps.

First, is your vacuum pump working? You will hear it when you turn the truck to ON and engage 4wd, you disconnect a vacuum hose (pump senses drop in pressure and tries to re-pressurize), or if there is a vacuum leak the pump will just engage for a few minutes as soon as you turn truck to ON. Assuming you’re able to get the pump to engage, let’s move on (otherwise replace the vacuum pump).

Next, is your solenoid working? Simply disconnect the vacuum line that comes directly from the pump and goes INTO your solenoid, and plug the vacuum pump line directly into the upstream vacuum line that’s headed to your hubs. Check my video for how to do this in detail. You will completely bypass the electronics of the 4wd system and apply direct vacuum to your hubs. If you have no leaks in the vacuum lines that go out to your hubs from the solenoid, then the vacuum pump should shut off in under 45 seconds (once it fully pressurizes).

Now if the vacuum hub continues to run for over a minute, you have a vacuum leak in your lines, but test whether your hubs are engaged by jacking up the front tires and spinning one tire with 4hi engaged. Your passenger tire and driver side tires should both spin together now (but in opposite directions if you have an open diff), but if your hubs are NOT locked, then each tire will spin completely independently of one another. This means you have a vacuum leak or your vacuum pump is not functioning (again this should be very obvious if it’s not, test the vacuum with your finger over an active line, it should suck air). To force your hubs to engage just spin the manual locking hubs to “LOCKED”.

If you have any questions, please comment below.

8 thoughts on “Ford Superduty 4wd hubs problem QUICK FIX (ESOF)

  1. Bob says:

    I have a 99 F250 superduty with ESOF, the light on the dash doesn’t come on and does not shift into 4wd. I can jump the relays and it will shift, it will work fine but after not driving for a week or so and try the 4wd again the light does not come on or shift into 4wd. Any advice thanks.

    1. josiah says:

      Hey Bob, it could be your hubs or solenoid, or a crack in your lines. There are two things you could try that come to mind. You can get a vacuum gauge (possibly rent one from your local auto store) that attaches to your vacuum lines and see if sufficient PSI is being pushed to your hubs when you trigger it after that time. I’m thinking that over the time the ambient pressure in your lines is slowly decreased and the pulse that is sent after a week is now insufficient. This would point to a bad solenoid most likely. You could also use many vacuum gauges to inject pressure into your hubs which would tell you what kind of PSI is needed to lock them. I’ve done this in the past to diagnose and it’s a fantastic tool for this, make sure you get one with many adapters for the different sizes (but you can always use tape for a retrofit).

  2. Mark Kirch says:

    I have a problem with a noise coming from my left(drivers) side hub trying to engage?? while I am driving. If I manually lock the hubs the problem is solved no noise, vibration or rubbing/trying to engage sound. I have a 2001 superduty with the 7.3 turbo diesel. My vacuum pump feeds to a vacuum tank, then to a solenoid. I found the right front vacuum line hanging due to a split, cut off an inch and reattached to the axle. There is no vacuum felt from either side when pulling the lines off the axle to the hubs. I have tested it in 2wd on the switch and 4wd hi on the switch. if this is a solenoid problem maybe then I would get vacuum? My pump and other parts are not the same as your video. I have found the pump and reservoir but am still looking for the solenoid. I have also been looking for a diagram of the routing of the vacuum lines but no luck so far. I may just go buy a length of tube to bypass the truck to test the system to see if I can get vacuum to the hubs and do the manual tire spin you showed in the video. That would at least show me whether it is the solenoid or lines right? Hope you have an answer as I have driving with the manual lock on so I don’t damage the hubs with them trying to engage or rub. Another mechanic said I may have a DRY hub??? But since no problem when locked I think it is a vacuum problem. I do need to know when vacuum should and should not be present. A buddy had a similar problem in his 2012 F150 but he said that there was vacuum present in 2wd and he found a leak in the hose near the hub that he sealed. But since he had the gas engine, different year and model it doesn’t seem to help me. Thanks for any help you may have.

    1. josiah says:

      Hi Mark, sorry for the late reply you got stuck in spam somehow. If you’re still having the 4×4 issue with your 2001 Superduty here is a little bit of help.

      I do need to know when vacuum should and should not be present.

      Vacuum SHOULD always be present in the lines (between the pump and the solenoid at the very least). Regardless if you are in 4wd or not, it is charged and ready to send a pulse to the hubs if you decide to turn on/off 4wd.

      The function of the vacuum hubs has been compared to a ball-point pen in that the action to engage is almost identical to the action to disengage. There is a vacuum pulse (not full-time) applied to engage the hubs and then the vacuum shuts off. To disengage, a similar (but shorter) pulse is applied. Those who think that the vacuum “holds” the hubs in a locked position are misinformed.

      If there is no vacuum in the lines when you turn the key to the on position, the vacuum pump will start to try and bring the lines to a “vacuum” state. The pump will turn off when the system reaches a certain vacuum strength. Don’t think it should run every time you turn on the key. So, (while the key is in the ACC or ON position) we know there should always be vacuum in the lines so if you pull a line off of anything, causing the lines to lose vacuum, then you will hear the vacuum pump kick on (if pump is functioning correctly).

      If you trace any of the vacuum lines from your pump you will find the solenoid. It’ll go from the pump -> solenoid -> then to each hub.

  3. Sean T says:

    Is the 4or vaccuum solenoid controlled by ground? PWM? I’ve got 13v on center pin on solenoid, and ground showing on other two pins, but the grounds wont light a test light.

    1. josiah says:

      I don’t actually know, hopefully someone else will chime in and document this for everyone, but in my video I demonstrate a method to bypass the solenoid to prove that all else is functioning.

  4. Roger FOLEY says:

    I have a 2008 Ford f350 super duty 4×4 single axle fx4 and when I put it in 4×4 it isn’t working but the shift lights are working and showing its in 4×4 high or low but isn’t going into 4wheel drive.i can here the silinoid switching over but only the back tires spin what could be wrong I’d appreciate some feed back.

    1. josiah says:

      Do the check I do in the video where I put it on jackstands, lock it in and check the front tires and whether they’re spinning or not, whether the front driveshaft spins, and then if the front driveshaft is spinning then try locking the hubs in manually and see if that changes anything. Get back to us with your results.

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