I have an 03 6.0 FX4 with auto lock hubs and I cant get them to engage. I have been reading a few other posts and from what I have read, if the air works anywhere besides just the defrost, then I don't have a vacuum leak. I tried out the hubs on concrete (only did that to make sure they were grabbing), a when I turned the wheel they would not grab. I then got out of the truck to manually lock the hubs to make sure that my 4WD was even working, and my front tires binded up when I did this so it was working. I then got out of the truck and turned the hubs back to AUTO (with the 4WD still engaged and the wheels still turned) to see if the hubs would disengage or stay engaged. I got back in the truck and put it in drive and started inching forward. The wheels were still binding, but before I could back off the gas there was a kinda big pop and my truck lunged forward. This kinda scared me at first, but I think all that happened was that my hubs were disengaging under a lot of pressure so they popped loose.

Anyways, moral of the story is...does anyone think that my problem is with my Pulse Vacuum Hub Lock Solenoid?

 

How many miles on the truck? The grease is probably got hard in the hubs, if they have never been serviced. My 04 does the same thing.. I just manualy lock them when needed..

 

It has 150k. I just got rid of an 04 that did the same thing also. But I also forgot to mention that the first day I had it I swithed to 4WD while going about 25mph and it did work but it hasn't worked since then. Kinda sounds like it could be the grease since you mention it. Is that something hard to service yourself? I went and bought a Haynes Repair Manual so that I can do my maintenance stuff myself instead of paying a fortune at the dealership. Thanks for the help though.

 

Its not that hard just do one side at a time of course, and make a mental/visual reference of how it comes apart.. The Kendal Super Blue wheel bearing grease is excelllent..

 

Ok. What exactly am I cleaning out and regreasing?

 

Figured out the problem...replaced the Pulse Vacuum Hub-lock (PVH) Solenoid and everything works great now. I talked to some mechanic friends of mine yesterday and they said that they had never heard of grease getting hard, so I just decided to take my chances with the solenoid and it paid off. TreeTech you should probably look into it cause it was only a $55 fix. I know you said you just lock them manually when you need them, but I know personally that any time I need my 4WD, that's usually when I least wanna have to get out of my truck. The convenience of auto-lock was definately worth $55.

So if anybody else is having this same issue with their auto-lock hubs and your air is working normal inside the cab, then I think it's safe to say that it's your PVH Solenoid. But TreeTech, you should swap yours out to confirm this.

Thanks for all the help everyone!

 

If you don't lock your hubs regularly then you will not cycle the hubs, they will not stay lubricated and then the parts will bind inside. It is recommended that you engage your 4wd system at least once a month to make sure you exercise the system and keep it working (hopefully) to it's maximum potential. Obviously the ESOF system is not the most brilliantly conceived idea, although it does still have a manual backup on the hub itself (although my dad's Chevy mechanical system is more reliable, when it breaks he is out of luck until it's fixed).

If you think you have a locking hub issue and you have an '03-'04 (leaf spring front end) you can check this out:

Welcome to guzzle's 4x4 Autolock Hub Lubrication Maintenance Web Page

I don't know if the '05-up is similar, but I have heard that when they changed to the coil springs up front that they improved the ESOF as well.

It's better than shelling out around $300 for a new locking hub...

Just my .02