Hey guys I have a question that can't seem to find a direct answer for.

Exactly how do the auto 4x4 hubs work in these excursions?

I've been told that they work off of a vacuum line that applies pressure to the hubs to engage them once you hit the button inside.

I've also been told that the vacuum line going to the hubs is actually some kind of vent? And that it doesn't actually engage the hubs.

Any info I could get on this would be helpful.

Thanks

 

Same as the Super Duties, to my knowledge. There is an air line; when you flip the switch the vacuum kicks on, sucks the air out engaging the hubs and the transfer case motor is electronically switched into 4x4.

Essentially the same thing as if you turned them in by hand.

 

it vacs to turn on and off. Just like an ink pen clicks in and out, only with vacuum. they get gummed uo from old grease and failed seals and normally why they quit. I just tore mine apart, cleaned and regressed them and they once qgan work great.. The engage and release vacuum pulses are driven from the vac relays and controlled from what I assume is the gem module.

 

Go to the Excursion Forum Tech Folder Sticky thread > Suspension, Steering, Brakes, Wheels, Axles, Hubs, Transmission/Driveline > Axles, Hubs, Ball Joints > ESOF And How It Works

Stewart

 

Thanks for the info guys, and I'll go check that page out Stewart.

I just have one more question.

If these are controlled by vacuum, then if one of the vacuum lines is cracked or broken behind the wheel going to the wheel hub, will that cause both hubs to stop working correctly?

 

If it leaks bad enough, yes. If it leaks really bad your heater will lose vacuum and default to defrost when you turn on the 4wd.

 

It can, but it doesn't have to. With an open front differential you will have no power to either wheel if one of them is unlocked. That's why you can override the vacuum system and manually lock them.

 

My dash vent and floor vent don't even work anymore at all- only the defrost blows whenever the heater/ac is turned on ... guess I must have a pretty bad vac leak

In the meantime I just turn the stock hubs to lock and flip the switch in the dash to 4x4H if I need it, and leave it that way for a few days and then turn the hubs back to Auto and flip switch back to 2WD.

Not to hijack -
Can I simply leave the hubs on Locked while flipping the inside switch between 4x4H and 2WD instead of having to turn them back and forth a few times a week without causing any damage if there is a leak ?

If there is a vac leak, will it keep the 4x4 from engaging , or staying engaged if I leave the hubs on AUTO and just use the inside switch between 4x4 and 2wd ?

 

Yes, you can leave the hubs locked and run around in 2wd. Lots of guys who live in areas where 4x4 is a way of life will do this.

A vac leak will result in the AUTO selection not engaging 4WD when the **** is turned. By locking the hubs you bypass the vac system. Locking you hubs full time does cause a little extra wear on parts but nothing crazy. If there is going to be a few days where 4x4 is needed often then just leave things locked. If not , just hop out when needed turn the hubs and go.

 

Two parts to system, the hub connects the wheel to its front axle half shaft. When hub is locked, the axle shaft for that wheel turns when you move. Manually locking it just ensures the wheel/axle shaft are "locked together"
The transfer case, when 4hi or 4lo engages sending power to the front axle, and then to each axle shaft, and IF the hub is locked the wheel will also get power.
So, in 2wd, manually locking one of the hubs just means that half of front axle is also spinning and your MPG goes down a bit from the wasted energy.
Conversely, in 4hi, with unlocked hubs you are spinning front driveshaft and both axle shafts, but the hubs are not using this power and your wasting even more power by spinning even more stuff.

 

I have found though that manually locking works almost 100% of the time with factory hubs. Manually unlocking though.... I have gone quite a distance with a hub locked that was turned back to auto. Now if I manually lock then unlock them, I drive a few yards forward and backwards, then reach up on each side and try to turn the u-joint to verify. Its the biggest reason to clean and lube them.

 

Yeah if they aren't unlocking they are a pain. I ran in 4 low while pulling a truck off road and then was stuck in 4 low for a day and couldn't drive anywhere. I switched to manual hubs.

 

Love this forum
Thanks for all the info !

 

"Exactly how do the auto 4x4 hubs work in these excursions?"


AS POSTED ALREADY : NOT VERY WELL !!!

 

The technical answer is that because the axle shaft spins inside the hub, the mechanism has to be free floating. So the stub axle spins inside the hub, and the locking hub is geared on both sides to engage both the stub axle and the hub, which transfers that power to the wheels. When the locking hub is disengaged the stub spins without transmitting power. When engage it locks the inner splines to the stub and the outer splines to the hub. Vacuum is the best way to actuate them since you can flow vacuum in and out of the hub and it doesn't interfere with the hub or axles ability to spin. The bad part is that you have to keep the hub sealed up tight or it won't hold a vacuum and the hub either won't engage or won't unlock, depending on which way the vacuum pulls. On our trucks, replacing the vacuum seals alone is about what a cheap set of aftermarket manual hubs costs. Junkyards are full of manual hub super duties though, and the oem quality is superior to all but possibly the most expensive aftermarket hubs.