4x4 won't switch ESOF, bucks while locked - Ford Powerstroke Diesel Forum
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Old 01-02-2012, 12:20 PM
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4x4 won't switch ESOF, bucks while locked

Been reading tons of other posts and not sure I have the answer I need. I have an 08 F250. When I have the hubs on auto and put it into 4x4 on the dash you can hear the motor try to engage but the 4 wheel doesn't lock. I locked the hubs and put in in 4 in a parking lot. It is dry and just did a few circles but the truck started bucking and getting crazy. Now I'm confused and scared. Does this sound like a hub issue? I need my 4 wheel drive. I'm scared that if I lock it and engage on a bad day I might still break something based on how it drove today. My a/c doesn't switch to defrost when i switch while doing electronic (not locked). I was at my buddies shop the other day installing a dpf delete and it didnt feel like there was vacuum when we disconnected the line from the hub but not sure if we checked proper. I really don't wanna pay for trouble shooting quite yet til I feel confident i know somewhat the issue. Mainly concerned about the bucking today. I really need to get this going. so lame. I'm driving it in 2wd now with the hubs locked to see if I can get the hubs lubed up a little.
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Old 01-09-2012, 10:55 AM
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the bucking is normal on dry pavement as our trucks have a "true" 4wd system.

Using the esof(or locking the hubs if esof isn't working) locks all four tires to their respective axles, to their respective front/rear diffs, and to the center transfer case and to the engine.

In other words, all four tires are locked together and want to turn at the same rate, which doesn't happen when you're turning in circles. Instead of twisting the axles or grinding gears, you tires hop/skip to make up the extra rotation/s.

"True" 4wd like on a truck should only be used in snowy/icy/offroad conditions, as driving it it every day will not be good for your truck. Its not a "AWD" system which has front/rear/center differentials to compensate for the different tire travel distances and prevent hopping/skipping.

You CAN drive with the front hubs locked if you want all the time, just not in 4wd. Driving with the hubs locked will spin all your front drivetrain components which may/may not affect your mileage, and will cause slight hopping during tight turns.

Basically, just use 4wd when you need it, and every now and then for short times to test it.
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Old 01-09-2012, 01:09 PM
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Great reply. Thanks. Any idea where I would start with identifying my electronic shift on the fly issue?
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Old 01-09-2012, 01:16 PM
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personally i have a 06 6.0 so i'm not that familiar with your truck.

But, on mine the issue was the vacuum solenoid was bad, causing a vacuum leak so the front hubs wouldn't lock. IT would shift in 4x4 when you manually locked the hubs and used esof, but not without manually locking them.

Traced the vacuum issue by jumping the in/out tubes on the solenoid and that fixed it so replaced the solenoid and everything is good now.

Maybe theres a similar part on your truck? Not sure if its the same on 6.4s but when you use the esof and it doesn't work, does your air only blow on defrost? On 6.0s that happens due to the vac leak, which is a dead giveaway its vac related and not electrical.
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Old 01-09-2012, 01:36 PM
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I tried that trick with the vents., they seemed to work proper when shifting it., it did not go to defrost. Dealer said that part is 85 bucks and not returnable so wanna make sure I try and trouble shoot pretty well. I'll try the vent trick again just to make sure here when I get off work.
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Old 01-09-2012, 01:49 PM
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My truck did the same thing as scottydosnntknow. What I did was traced down the vacuum lines and tested them. It was very easy because there only a couple. If your truck is the same as the 60, you will have the vacuum pump on the inner fender, from that a line goes to the tank right beside it that holds the vacuum, then a line runs from that to the vac. solenoid, then from there to the hubs. I jacked up the front of my truck and ran a vac hose from the pump directly to the line that runs to the hubs. Turned the key on to let the pump pull a vacuum on the hubs and tried to spin the front wheels, in my case they were locked in, so that told me the hub seals were fine and the line was fine. Since the pump does not stay running all the time i knew it was not the line between it and the solenoid so that makes it a bad solenoid. The system is very simple. I also had a vac gauge so I was able to watch everything with that as well. I hope this helps, again my truck is an 05 but I would think the systems would be very similar.
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Old 01-09-2012, 01:52 PM
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all you need to do is unplug the intake and outtake hoses to the solenoid under the hood. It'll start to draw vacuum as soon as you unplug it though on the "intake" side from the resevoir so it'll help to plug it with a pen or something. Then use a small jumper hose of some sort to connect the two together, then turn the key to accessory. The vacuum pump should start up as it always does to vacuum the resevoir and it should stop in a minute or two once it reaches vacuum. If it runs and runs and runs that means you have a vacuum leak downstream from the solenoid, or your jumper isn't sealed.

at that point when its stopped, switch the esof switch and you should hear the click in the transfer case and it should be in 4wd. If it works then, your solenoid is bad.

If the vacuum pump runs and runs and runs, trace the hoses one at a time to your hubs. Unplug one side and plug it, then try the test again. Switch sides and do the same thing. If it holds vacuum on both sides, then its probably one of the hubs leaking.
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Old 01-09-2012, 02:45 PM
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awesome advice. I'll hopefully be able to test this by the weekend. I'll report back once I know.
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Old 01-09-2012, 03:08 PM
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Your truck is engaging into 4wd, that is why it was bucking in the parking lot! that is normal for it to do that on a dry hard surface.
But it is not good for you to use 4wd on dry pavement because you could break something, it should only be used on wet or slippery surfaces.

Your issue is strickly the auto hubs locking when in the auto position which means you have a vacuum leak either on a vacuum hose, or at a seal behind the hub.

You don't have to worry about using 4wd, when you need it just turn the hubs to "Lock" and shift into 4wd. The "Lock" setting is a backup just incase the "auto" setting doesn't work!

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