sd250 has shift on the fly 4x4. what is the hub system really for and how/when to use?

 

Welcome to FTE, mrpjr!

When in 2 wheel drive, the front hubs allow the front wheels to spin without having to spin the front axles and front driveshaft. This saves fuel, makes the truck a little quieter and supposedly saves on drivetrain wear.

When you put the truck in 4H or 4L and the hubs are in AUTO, the hubs lock the wheels to the axles. The transfer case sends part of the torque to the front axle, which turns the wheels.

If the hubs fail and you need 4 wheels drive, you move the hub selector from AUTO to LOCK, which manually locks the hubs to the axle. YOU ARE NOT IN 4 WHEEL DRIVE AT THIS POINT. It doesn't hurt anything to drive the truck on dry pavement. You would still need to put the selector in 4H or 4L to be in 4 wheel drive.

 

so they should always be in auto unless they fail correct.....then when you want 4x4 you just turn the **** on the fly

 

thank you. im confused...so if i go to 4 wheel high or low i don't need to change from auto to lock?

 

That's the idea. But, if you are spending a week climbing around the Big Horn mountains, frequently moving in and out of 4wd, why not just leave them locked and avoid any chance that they won't work, or work quickly enough when needed.

Bill

 

Correct. The AUTO position makes it truly and fully shift on the fly. No need to get mud on your wingtips. The LOCK position is when you want them to remain locked while whether in 4x2 or 4x4 hi/lo mode.

Bill

 

Yes, normal operation of your truck would mean the hubs stay in AUTO.

It is a good idea, say once a month or so, to put the hub in LOCK and drive a few miles in 2 wheel drive, without shifting into 4 wheel drive.

This just rotates everything a little for better lubrication.

 

Welcome to the site.

This along with many other things are covered in your owner's guide. It is a very good idea to take an hour or so of your time to read through it. If your truck didn't come with one you can enter your year and model at the following website and download one for free.
http://www.motorcraftservice.com/vdi...&menuIndex1=18

Also the first thread in this forum is the Tech Folder. By following the links in it you can answer a lot of the other questions that you will soon be asking.

 

one of my hubs was in the auto position and one was in the lock position did this cause any damage to my 4x4.......

 

No, but it may cause uneven tire wear, premature baldness and halitosis.

Seriously, it isn't good to do this. You're creating more friction drag on one side of your truck, which might create an unsafe pull in the steering.

 

[QUOTE=redford]No, but it may cause uneven tire wear, premature baldness and halitosis.
QUOTE]

Danged now I know where the hair went.

It might also cause a slight drift when driving to the side with the locked hub due to drag of the axle and gear drag.

There is a note in the manual about not using 4WD on dry paved surfaces.

 

Yes there is, but if you lock the hubs but keep the transfer case selector in 2 wheel drive, you are not in 4 wheel drive and will not hurt anything.

Since I have manual hubs I lock my front hubs if I think I might need 4 wheel drive. (Snow or off road). That way, I don't have to crawl out of the truck later to engage them, I just put the transfer case in 4H and off I go.

 

now do you have to stop to put it in 4x4 if you leave the hubs locked, or can you shift into 4x4 with the truck moving

 

You can shift while it is moving....but be reasonable. Don't try it at 80 MPH or when accelerating fast.

 

One other thing to mention. Do not try to make sharp turns in 4 wheel drive, or with the front hubs locked. That puts a lot of stress on the front U joints.