4 Wheel Drive Engaging - Ford 7.3

[rgood]

Guys, I recently bought a 2000 Ford F250 - 7.3

It has the In-Dash SWITCH to engage the 4 WD.

It also had the lock in - lock out hubs.

My question is - Does the Dash switch control the lock-in/lock out hubs too?

Or is it only engaging the 4WD?

I ask this question as when I'm driving up and down the highway, I want the fuel economy of the Hubs being locked out. So, if my hubs are manually locked out, and I engage the indash switch, is it in 4WD? The dash light says it's in 4WD.

Or to ask the question another way - What do I have to do to use the 4 WD -You would think the operation manual would clearly explain this, but it's about worthless. Thanks!

 

[Reg]

Guys, I recently bought a 2000 Ford F250 - 7.3

It has the In-Dash SWITCH to engage the 4 WD.

It also had the lock in - lock out hubs.

My question is - Does the Dash switch control the lock-in/lock out hubs too?

Or is it only engaging the 4WD?

I ask this question as when I'm driving up and down the highway, I want the fuel economy of the Hubs being locked out. So, if my hubs are manually locked out, and I engage the indash switch, is it in 4WD? The dash light says it's in 4WD.

Or to ask the question another way - What do I have to do to use the 4 WD -You would think the operation manual would clearly explain this, but it's about worthless. Thanks!

I think you need to lock the hubs FIRST.
Then you can use the dash switch.
I think the rumor about economy when running with hubs unlocked is bogus.
It supposes that the drag in the axle and bearings represents a significant work load - - in the scale of moving probably ~7,500 lbs of truck around it is negligible.
You could save more fuel by turning your engine off at stop lights.

 

[cp1969]

If it takes 5 ft-lb to turn the driveline (I have no idea what it actually takes, but 5 ft-lb doesn't seem like much)

And the driveline spins at 2000 rpm going down the road

Then it takes about 1/10th of a gallon per hour (about 30 cents per hour today) to spin that driveline.

 

[Diamondpilot]

I had a 2004 and a 2006 f-350's with diesels and I was told that the hub was simply a backup to the dash switch. As I remember it there was a AUTO selection on my hubs but these trucks were later models than yours.

Chris

 

[ScottAR]

The manual hubs are a backup in case the button doesn't kick the hubs in.
Really nice feature if you ask me. Takes away most of my objections to electronic 4wd besides the "more complex than needed" angle.

 

[Dmace]

The hubs allow you to drive around in "unlocked" or "automatic" position. The "automatic" position keeps the front-end disengaged until the driver engages 4-wheel drive from inside the cab.

It's not a backup, you still need the switch to activate the hubs.

 

[RayH]

The button on the dash engages/disengages the transfer case. The manual hubs engage/disengage the axleshafts at the hubs. The manual habs are not a "backup" for the dash switch, they are for two seperate things. If you engage the transfercase without engaging the hubs, you wont have 4X4. The front driveshaft and front axle will receive power from the transfercase but it wont get to the road because the hubs are not engaged.
If you engage your hubs but not the transfercase, the front wheels will turn your axle and driveshaft when you drive. Its perfectly exceptable to leave your hubs engaged in the winter or any time you may suddenly find yourself in need of 4WD, that way you dont need to climb out in the weather or the mud to engage them.

 

[skipmarcy]

No one has quite gotten it right yet, almost but no cigar. The dash switch must be used to engage the transfer case, no if ands or buts. It shifts it from 2wd to 4wd high or 4wd low all in the transfer case itself, just like the old manual shifters did.

When the hubs are in the manual free position and you turn the switch on, the transfer case turns the axles and an automatic clutch in the hub engages the hub to give you drive. These clutch assemblies in the hubs can give trouble and not engage for various reasons - too cold temperature making the grease real stiff is one cause, worn parts, wheel in a bind, etc. Even when they do work, it usually takes a revolution or two of the wheel to engage the hub. If you are stuck solid or the hub fails to engage automatically, you can get out and manually turn the hubs to overcome the automatic portion not engaging. You must return the manual hubs back to free once you're out of your jam. The automatic hubs will disengage automatically when you turn the switch off (back to 2wd) after a few feet of movement(as long as the hubs are back in the free position manually). In my Nissan, you have to move in reverse a few feet, then go forward a few feet for them to disengage. The Nissan doesn't have the manual overide hubs, totally automatic. In my F250, they disengage without reversing any, just drive a few feet in either direction knocks them out.

Do not run the front hubs engaged either manually or automatically at highway speeds or on hard, dry surfaces. These 4wd systems are not the same as an all-wheel drive system !!! They are not designed to be operated at speed !!

 

[RayH]

Wow, auto/man hubs, thats a nice arrangement. I must be behind the times, my old 97 7.3 had run of the mill manual hubs. when did Ford add the auto option?

I disagree with you about running on dry roads with the hubs manually engaged. If the transfercase is in 2WD, the front and rear drivelines are not connected together, aside from a little more noise and a different feel, there shouldnt be any bad results from leaving the hubs engaged, unless theres something Im missing about the bearings or lubrication of the front axle, in which case, you shouldnt drive it for extended periods in 4WD either.

 

[firemanpat2910]

Buying a used truck means there is no answer without more questions. do your hubs say "Auto" and "lock" or "Free" and "Lock" ? One of the first things alot of owners upgrade is the Auto Shift On the Fly hubs. They routinely replace with 'Warn' brand hubs. On my 07 and my buddies 01 F250s when you turn the little knob on the dash it uses vacuum to activate the "Auto" hubs. If we are going some where that I Know we will have to lock in I will stop some where that I can get out on "Clean dry ground" and pre "Lock" my hubs so that if a vac hose is bad I dont have to get wet feet to "Lock" the hubs. If I just bought a used truck I would test the auto locks. simply chain hitch to Solid tree. put hubs in Auto put dash switch in 4hi SLOWLY drive forward to take slack out of chain. when chain is taught give it enough gas to spin the wheels. stop put in park get out and see if front wheels tore up any grass then repete with hubs in "Locked" position.

 

[onsight]

Since your truck has the switch in the dash, It has shift on the fly. Leaving the hubs in the AUTO position, they will lock/unlock through vacuum as you shift into 2 or 4 wheel drive.(hopefully - the hubs themselves sometimes fail). Turning the hub to the LOCK position manually locks the hubs (wheel ends). You want to LOCK the hubs if you know that you will need 4WD (mudding or snow plowing). When your hubs are in AUTO - they dis-engage and engage with each change of direction (forward/reverse), which is pretty hard on the front axle.

 

[Diesel-ME]

One other note - if you get stuck prior to manually locking in these type of semi-auto hubs, be SURE to manually lock the hubs, else they will auto-engage during wheel spin - causing a huge CLUNK, and perhaps hasten their demise...??.... You only want to use the dash switch when you are moving.

~paul

 

[Flywheel]

FireMan has the best reply - i'll add a bit...

The dash switch will operate:
1) transfer case
2) Pulse vacuum hublock system

With the hubs in "Auto" or "Lock", you are able to shift the transfer case between 2WD and 4WD during normal driving (without wheels already spinning-out).

For 4Lo - you must be in park or neutral, foot on the brake and not moving - to get in and out.

The switch on the hubs allows for freewheeling in "Auto" if you are in two-wheel drive - or manually locked in the "Lock" position. Many folks just leave them locked for the winter to anable seamless angagement / disengagement.

You will be fine running with the hubs in lock on any road - however, you may notice some u-joint binding at full lock, since the spindle is turning.

When you leave the hubs in "Auto", and select 4Hi, a signal is sent to the 4WD module, which engages the transfer case, then the light on the dash lights. Another signal is also sent to the Pulse Vacuum Hub Solenoid. A vaccum pulse is then sent from the vacuum reservoir (you have a vacuum pump and reservoir on the passenger side above the wheel well (diesel)) to the hubs to engage them. A diaphragm in the hub will pull the gears together and they engage similar to a click type pen - a push to engage and a push to disengage. - So along those lines,, when you go back to 2Hi, a short pulse is sent to disengage the gears in teh hub to allow freewheeling.

There are inherent problems with the vacuum hub system - vacuum leaks. Symptoms of a vacuum leak are that the vents will revert to defrost for about 30-40 seconds. Since the vents run ont eh same vacuum system, they go to defrost as a safety - so you can see...

A good tip for your tranny is that when backing a heavy load or moving through a field at low speeds, disconnect the vacuum solenoid and put the truck in 4Low - this will reduce the stress on the tranny clutches - reverse is especially susceptable to overheating when backing - so 4Low can be a saver. This will engage 4Low in the transfer case, but not egange the hubs for easier maneuvering. There is a modification you can do for an in-cab switch to ever-ride the vacuum solenoid.

More information can be found on thedieselstop.com

Congrats on the "new" truck

-Flywheel

 

[rgood]

***There are inherent problems with the vacuum hub system - vacuum leaks. Symptoms of a vacuum leak are that the vents will revert to defrost for about 30-40 seconds. Since the vents run ont eh same vacuum system, they go to defrost as a safety - so you can see...****

This is very interesting - Thanks to everyone for the Posts! Flywheel, I have this problem you describe above - How hard/expensive is it to fix???

 

[Flywheel]

Rgood,

It may not be hard to fix at all - just takes a little inspection and troubleshooting.

The common leak occurs where the vacuum line attached to the nipple on the hub. Heat causes the rubber tubing to become brittle and crack. You can just cut off an inch and reattach.

Other than that, try to follow the lines from the vacuum solenoid. Plug the line going to the hubs with a golf tee. If the vents still revert to defrost, then the leak is in the solenoid. If the vents do not revert, then isolate each hub with the golf tee. THere are a couple of seals in the hubs that can go bad - especially if you have a bad hub. Check these by lifting the front axle and trying to "wiggle" the wheel back and forth at 12 and 6.

PM me if I can help more.

 

[rgood]

Thanks Flywheel ! You fixed me right up - I could feel with my hand that the vacuum hose to the right hub was cracked in the back - I need to replace the hose, but the quick fix was to just cut and reattach as you suggested.

Thanks Again !

 

[Blk88GT]

You may want to join TheDieselStop.Com - www.thedieselstop.com and ave a read.

 

[Flywheel]

rgood - just regular vacuum line hose from the auto parts store is what I put on my truck 4 years ago. A good indication the it is going bad is when it leaves your hands black.

Good tip again on thedieselstop.com - I'm addicted.

 

[ddivinia]

Guys, I recently bought a 2000 Ford F250 - 7.3

It has the In-Dash SWITCH to engage the 4 WD.

It also had the lock in - lock out hubs.

My question is - Does the Dash switch control the lock-in/lock out hubs too?
------

That switch does it all. XFER case and hubs. You can do the hubs manually in case of failure. Look on the hub, youwill see hoses going to operate the hubs.

D.

 

[horse7]

Also be sure the hub seals are in reasonably good condition. The vacuum can suck dirt and water into the hub with unpleasant results if the seals are bad. This is one of the main objections to the ESOF (electronic shift on the fly).

In my case I wanted ESOF since frequently the only need for 4wd is while on the driveway, and manually unlocking after getting out of the driveway (to avoid the slight reduction in mpg w/locked hubs, and to avoid the slight increase in wear) is an aggravation. Had to do that with my old Blazer with manual New Process/Spicers, tho mostly just stayed locked all winter due to the hassle.