Hi all, 05 f-350. Been trying to get the 4wd auto locking feature to work right. I figured I throw it out here to see if anyone else has better ideas. 4wd is able to auto lock but only at complete stop in drive. If I'm rolling forward at 10 or 20 mph and engage the auto 4wd, ac will go to defrost vents like a vacuum leak. Things done so far: new vacuum line from hub all the way up, auto locking hubs have new o-ring and gasket, new pulse hub solenoid. Everything is sealed and plugged in where it should be. Tested the hubs and both hold pressure. Auto 4wd function works, but I thought we can do it while driving, right? Mine can only be done from a complete stop. Weird.

Thanks in advance.

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Did you check your owners manual? I remember reading about coming to a stop or atleast slowing down.

 

Sorry I don't have one. Didn't come with truck. I thought so too. I'm just trying to confirm if I'm supposed to or not. For an 05 of cos. Thanks.

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If no one else responds by the time I get back to my truck, I'll check.
The last F250 or Excursion I worked on acted as you described. I thought I read it in the manual that it was normal. I have full manual 4 wheel so it's not something I experience much.

 

From the 2003 manual

"Shifting from 2WD (2WD High) to 4x4 HIGH (4WD High)
Rotate the 4WD control to the 4x4 HIGH position at speeds up to 88 km/h (55 mph). The electronic shift 4WD system is designed to engage 4x4 HIGH (4WD High) when the vehicle is moving. If shifted to 4x4 HIGH (4WD HIGH) while at complete stop, 4x4 may not engage and the 4x4 indicator may not illuminate until the vehicle is driven above 8 km/h (5 mph)."

 

interesting. thanks for the info. i wonder if they changed out the auto-locking hub when they went to the 2005 model. mine is working but entirely opposite to what u just posted. lol. 4wd high engages at a complete stop, but when i'm rolling forward slowly, the ac shoots to defrost vents.

i'm beginning if the axle vent hose may be clogged and if tat would be affecting me now.

 

You checked the hose on both sides... the full length? Disconnect at the vacuum reservoir and pump it from their. Its right near the battery. Only two lines come off the reservoir, the hubs and the heater controls.

Either way, you have a vacuum leak if it switches from the vent to defroster. If the hubs hold from the wheel well to the hub, then the leak is between the elbow and the reservoir.... or it could be the heater controls hose as well, you'll need to check it all.

 

From your description, your system looses vacuum to the hubs *only* when the vehicle is moving. If so, the problem is probably in one of the 2 vacuum seals in a front wheel assembly.

If you have a vacuum source (mity-mite or equivalent hand pump with gage) connect the pump to the nipple on the hub, pump it up to about 10 in of vacuum and see if it holds vacuum for a minute or so.

Repeat this test with the wheel off the ground. Spin the wheel and push it around to simulate driving. If the vacuum drops when you do this, a seal (probably the inner one) is bad.

If both wheels pass this test, I would look to see just what level of vacuum is being sent to each hub when you switch to 4WD. Disconnect a line at one wheel and place a vacuum gage on it. Switch to 4WD and see what the vacuum reads. You need to have a minimum of 8.5 inch vacuum or better to engage the hub. If this vacuum is marginal, there is a leak somewhere other than the hub/wheels.

You should be able to go into 4WD high when moving - my '06 does this OK.

Lou Braun

 

Yes sir. Changed the entire vacuum line. Changed the connector line from main vacuum line to vacuum pump to tank to solenoid. That's one piece. Everywhere from top to bottom holds vacuum, even at the hubs.

Thanks.

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Thanks Lou. I tested with a hand pump and gauge and it holds vacuum at the nipple on both sides. I will test the vacuum going to the hubs.

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Dom how you been

Seams like my 03 hub has 3or 4 seals per hub

But I know your 05 setup is different

Kinda an odd issue you have going on

Could be A wire issue or leaking vac when moving due to vibrations

 

What's strange is that you said when switching to 4x4 you get defrost. Only two lines off that system, hubs and heater control.

See if you can get the hubs to switch. Jack the wheel up and apply the vacuum and spin the wheel by hand when doing it to see if it locks. If it does, then it's up stream for sure. The pump may not be strong enough, it needs a bunch of vacuum to lock it.

Move the selector switch in the cab with KOEO and listen for the transfer case to switch as well. That part is all electronic, no vacuum involved.

 

I'm thinking a weak vacuum pump


Josh

 

You lost me

The heater going to defrost during 4x4engaugment is a classic symptom of a vac leak

Hvac leval control is vac controlled at least in my 03


Josh might be onto something
Or a leaky vac silinoid is common

 

That weak pump idea makes sense. When switched to 4WD, the PHV valve routes vacuum to the hubs. The vacuum would be supplied from the vacuum canister initially. Since the 2 hubs and associated tubing represent a large volume, the pump has to kick in to restore the vacuum.

If air switches to the defroster vents and then goes back to normal, the pump might be the culprit. I believe that the system keeps vacuum applied to the hubs for 45 sec to a minute. if the ventilation system switches back to normal within that time it could indicate a pump problem. If the ventilation system does not go back to normal until the PHV valve turns off, then it would be a leak. Ore something like that...

Lou Braun