Hi there,
I recently bought my first vehicle, a 99 F250 SD with a V10. My truck has the switch in the cab for 4x4, and has the hubs that say "Auto" and "Lock". The manual is sort of vague on what I can do with it. So I am coming here asking, can I shift while moving? If so, how fast should I be going? Is it harmful to the 4x4 to drive at highway speeds? Do I need to back up when I disengage the 4 wheel? I have tried the switch, and it doesn't seem to work. I did replace a vacuum line on the drivers side. What else is there to know?

 

Yup, it's designed to engage while driving.

I've seen some years recommend no more than 55 MPH to engage, other years there is no speed recommendation.

Not at all, there is no maximum speed once you're engaged.

There are a few parts of the system that can be prone to failure. Does the indicator light come on when you engage 4-hi?

 

Congratulations on picking such a fine vehicle for your first purchase!
Yes, the owner's manual can be a bit confusing in this area.

Hubs:
You can leave them in auto or in manual. If you leave them in manual, 4WD is not engaged, but the hubs are locked to the axles which will cause the 4WD to engage (when selected) whether the vacuum lines work or not. It will also hurt your gas mileage a bit. If you expect to encounter slippery conditions, you may choose to lock your hubs in advance.
4WD is not engaged until you use the shift on the fly switch in the cab. This engages the transfer case to send power to the front driveshaft and front axles. If the hubs are locked, 4WD is engaged, if the hubs are in auto and the vacuum system works properly, 4WD is engaged.
Yes, you can shift while moving. No, you don't have to back up to disengage. It is not harmful to drive in 4x4 Hi at highway speeds. Just don't do it on hard, dry, surfaces. Do not shift into 4WD if the rear wheels are slipping.
4WD Lo will not engage if the vehicle is moving.
You can engage 4WD Hi at any speed, and can shift from 4WD Hi to 2WD at any speed up to 55 MPH.
You do not need to back up to disengage 4WD.

Something else to be aware of:
the front differential is an open differential, this means that power is transferred to the wheel with the least resistance. If one wheel is on ice and one wheel is on dry ground, the wheel that is on the ice is the one that will spin.
the rear differential may be an electronic locker, or a limited slip, or an open differential as well. A limited slip differential should direct power to both wheels equally, or nearly equally, but is still able to slip the wheel with the greatest traction. An e-locker will direct power to both wheels equally.
Without a locker, it is still very possible to get yourself stuck in the right conditions, so drive accordingly.

 

Thanks guys!

wrvond, how do I know what kind of rear diff I have?

 

Not at all, there is no maximum speed once you're engaged.

Technically true, but I have not seen a case where I wanted to go faster than about 55 in 4WD. If you're going that fast, the road should offer enough traction to be in 2WD.

 

Sorry, I gave you some bad information earlier. I just finished reading your entire owner's manual, and electronic locker was not an option available for your vehicle.
That leaves either the open differential or the Track-Lok differential.
The Track-Lok is, for all practical intents and purposes, a limited slip differential.
About the only time this become really important is when you change the oil in the diff. The Track-Lok most likely requires a friction modifier additive, so you'll want to know what you've got beforehand.

There are a couple things you can do to determine what you've got back there.
1. Look for a metal tag attached to the differential. If the tag is still there, write down the code and look it up online.
2. Jack the rear of the truck up so that both rear tires are off the ground.
Caution - do not lift the truck by the differential. It's tempting, but don't do it. You can damage the housing as well as the seals where the axles enter the diff.
Rotate one tire by hand and observe the other tire. With an open differential the opposing wheel will rotate the opposite direction. With a limited slip differential, the wheels should rotate the same direction.
3. Look at the vehicle safety data plate attached to the driver's door or door frame. At the bottom there is a spot for the axle code.
Once you have that code, go here to look it up: http://www.blueovaltrucks.com/tech/f...le_codes.shtml



On another subject, since this is your first truck - I strongly encourage you to keep your tailgate locked. They are a very popular theft item and very expensive to replace.
There is a mod where you can place a hose clamp around the hinge socket that the tailgate pin lifts out of (passenger side) to make it harder for thieves to make off with your gate as well.

 

Welcome sir,
The tag that is under one of the cover bolts, at the back of the housing, actually tells you what gear ratio, and wheather it is a trac-lock or open.

Mine for instance has the off road package, denoted by the flashy decal on the bed side.
That package generally has the trac-lock , or limited slip .
On the tag , it will say as an example , 3L73.

That means it has 3:73 gear ratio and the limited slip .
This is the easy method.

 

Or you could look at the axle code on the door sticker. Let us know the code.

 

Thanks guys! I'll look at it tomorrow.

Where should I be jacking on?

Also, I tried it this morning, I hit 4 hi in the cab and the gave it some gas on an icy spot while I watched the front wheels, they did nothing. So is there a possible vacuum leak somewhere? Where are the normal spots for leaks?


That's good to know! I just need to lock it with the key right? I'm glad you say that because I drive it every day to my welding class (some daily driver, right?) and I'm always careful to never leave anything in the box, except the pail of grit and pail to stand on to work on the engine, if I ever need to. I also never leave the receiver hitch in.

 

99F250,
I am a fairly recent purchaser of a 1999 F250 SD V10, 4x4 also. Couple months now. The 4x4 on mine worked, but found that the hubs were locked all the time, both sides, even though the hubs were supposedly in the AUTO position. Could not move the selectors manually either.

I found that the vacuum lines had long been gone, removed, so there was no way they would operate automatically. I had a heck of a time removing the hubs, which should have been an easy job. I had to spray with PB Blaster, soak, pound and chisel, mine off. Took me several days on both sides. Mine were rusted, corroded, to the splines.

Once I got them off, I cleaned up the splines on the wheel bearing hub assembly best I could. That took a while too. Then decide to go with after market manual locking hubs. I went with the Mile Marker brand. I have used Warn hubs in the past on other vehicles, but these were a lot less $$.
So far, so good. They lock & unlock smoothly and work great!

I left the center caps off my front wheels for now. The new hubs don't extend out as far as the factory auto hubs, so looked odd, and a little harder to reach. Might put them back on when spring gets here, and not as likely to need four wheel drive. Sure is nice driving down the road now with both front hubs in the "free" position. It has to help, but I don't think the mileage will get much better. LOL Havn't checked mine yet, but hoping for at least 10.

If you live in a area where they use road salt, etc., like they do here in Ohio, checking and keeping the hubs free & lubed should be a high priority.






Gregg,

 

Hi Gregg! First off sweet truck! I do wish mine had an 8' box, but what the heck. Oh, and I forgot to add a pic of my truck before, so here's one:


Yeah, I do live in a salty area. I have thought about replacing the hubs, as the passenger side one has a badly cracked ****. I was thinking on just getting Ford hubs, but I'll see what my options are. How did you know that the hubs were always locked? Could you move the ****?

I was getting about 10 before I replaced the CHT sensor, so I'll find out later this week, as I just filled up today. When I bought it I was getting about 13.


I looked on my Door and found this, and I think it's for the axles:

Front GWAR Rear GWAR
PNVE AV PNVE AR

 

Nice truck!!! First thing I did with mine was get new tires, and alignment. But shop told me they couldn't do the alignment because it needed ball joints & tie rods replaced first. That estimate was $1,900. I decided to do the job myself...LOL

When I jacked up the drivers side of the truck to begin work, is when I noticed that the front shaft would turn when I rotated the wheel/hub. And it was in the AUTO position. Could not move the selector **** at all. Thats when the real pain part of the job began for me. Getting the factory auto lock hubs off. The outer splines were totally corroded/rusted together.

Both sides were the same. I guess the good part about them rusting together in the lock position was I had 4 wheel drive available. lol Just couldn't free the hubs.
All is well now, with the Mile Marker manual select hubs. Lock them and turn the wheel, the drive shaft turns. Turn them to free, the shaft does not turn.

Believe it or not, removing the old AUTO hubs was worse than removing the ball joints! Thats how bad they were. I had intended to just use the original AUTO hubs after some lube & service, as if they were just manual hubs. Because the vacuum part of the system was non existent all ready. But I had to destroy them, to get them off.

Gregg,

 

Here's a website that will walk you through finding and understanding all the codes on your truck: Super Duty Identification Codes

It is from a 2003 manual, so it should cover your truck. Let us know what you find out!

 

Thanks! I'm sure mine needs ball joints too, that'll be a spring project!

Well, giving that everything is stock on my truck I have a :
31 — 3.73 non-limited slip, F-250/Excursion

What does the 3.73 mean?

 

That is the ratio of the speed that the pinion gear rotates to what the larger ring gear rotates within the differential. This means that for a 3.73 to 1 setup, your driveshaft will spin the pinion gear a total of 3.73 times before one full revolution is completed with the ring gear which in turn spins the rear tires through the rear axles.
The larger the number, the more torque that will be delivered to the wheels. For example, a 4.10 gear will spin the driveshaft 4.10 times to turn the axles one time. This will allow for moving heavier loads more easily, but it will also use more fuel.
Everything is a trade off.

Non-limited slip means that you have an "open" differential - so power is directed to the wheel with the least resistance. If one wheel is on ice, and the other is on dirt, the tire on ice will spin and the one on dirt will not turn. A trick that you can practice that can compensate for this deficiency is to apply the parking brake. This will introduce the same amount of drag to both wheels, which will cause them to both turn, allowing you to get "unstuck".