Hi all,

My 2003 F-250 all of a sudden developed the problem of the front hubs not locking. The HVAC system works perfectly, so I don't have a vacuum leak problem. The truck is used mainly in the winter to plow my shop and home driveway, however I drive it to work 1 day a week to keep it exercised, and I always engage the 4WD to keep that exercised also. I had it in 4WD last Thursday, and it worked perfectly. On Saturday we got about 8 inches of snow, and when I turned into my street at home I flipped the 4WD switch, and the only thing that engaged was the transfer case--no hub engagement. I pulled the vacuum connector off of the vacuum solenoid and there's plenty of vacuum there. I hooked a mighty-vac the the other hose and pulled a good vacuum, and it did not drop, so there is no vacuum leak in the hubs or hoses to the hubs. What are my chances that the problem could be as easy as a bad vacuum solenoid ???



RON

 

Sounds like you need to switch the hubs to manual and make sure they work that way.

 

If you have vacuum then the selonoid is fine, remember that it only takes one of the hubs to not work for you to lose 4wd.. I suspect you have a sticky hub that doesn't want to lock in, you could engage 4wd and jack up each wheel to see which one is not turning the axle shaft when you spin the wheel. That will tell you which hub is the problem..Or get rid of them like I did and put on a set of Warn manual hubs..

 

I just had this problem last week with my manual hubs. I just cleaned and greased them this last fall and I'm thinking the grease I used may be a little too sticky for cold weather. The temps dropped below zero overnight. I parked it inside our heated shop for a day and they now work fine. Probably gonna re-service them with some lighter grease.

 

My 02 ended up a vacum leak in one of the lines and it disabled the 4x4 engagement. Noting that I thought it was the switch, seemed logical.

 

I'm replacing my axle seal and hub o-ring today as my 4x4 is not engaging. I was hoping it was something simple as a cracked vacuum hose, but it was not. Driver side hub would not hold vacuum.

 

You guys didn't understand my post correctly. I have great vacuum supply to the vacuum solenoid. If I unplug the vacuum connector to the solenoid and apply a vacuum to the line going down to the hubs, it holds perfectly--there are no vacuum leaks between the solenoid and the hubs. It appears to me that either the vacuum solenoid is not operating or it is not getting the signal from the 4WD module to engage the hubs. What is more common--the solenoid going bad or the 4WD module going bad ???


RON

 

Have you checked your fuses? Also check the vacuum from the pump motor to the solenoid.

Also, check your vacuum "system" by turning on your heater to blow on the floor position, switch to 4x4 on the dash and see if your heater defaults to blow out of the defrost vents.

 

I understood what you said just fine.
It still sounds like a malfunction in the hub, which is a mechanical engagement.
One of the hubs is not engaging as in stuck if your vacuum system is as you stated.

 

Note I stated previously that I had a vaccum leak. The leak was in the seal. Change the seal but make sure you put the new seal with the right side up.

 

If I remember correctly the seloniod sends a vacuum pulse to the hubs and not a constant vacuum, it sends one pulse to lock the hubs and another pulse to unlock. I still think you have a hub that is not engaging, it doesn't matter if the lines hold a vacuum if the hub doesn't pull in..

 

OK, my problem is solved. The vacuum solenoid on the right fender was bad. Something fell apart in it and stopped it from working. I took it off the fender and shook it, and something in it was rattling. I got a new one--no rattle. I installed it and everything is working fine.

I went through the diagnosis in the shop manual, and discovered what makes this system tick. To engage the hubs, the solenoid sends a 45 second pulse of FULL MANIFOLD VACUUM--in my case, that was 20 inches of vacuum. When you switch back to 2WD, the solenoid sends a 15 second pulse of PARTIAL MANIFOLD VACUUM--in my case, only 6 inches of vacuum.

Lucky for me, the solenoid is the least expensive part of the system. I got it for $59 online.



RON

 

Glad you found the problem and it wasn't bad on the wallet. best news the truck works fine.

 

I have an 05 f150 xl. When I engage my 4x4 the light come on it locks in. I can see my front drive shafts tturning but my hubs are not locking. I've found and fixed vaccume leaks. It has vaccume what would be my next step to diagnose the problem before replacing parts