Last year my brother got stuck in the snow with his 2008 F-250 4x4 and as I watched him try to get out I noticed that only one front wheel and one rear wheel was spinning. Could someone explain. Thanks.

 

my dodge durango does the same thing but it comes down to if you have a limited slip/locker or an open diff. If you have a limited slip or locker then both wheels will spin if it has an open diff the wheel with the least traction will spin. My f250 has a limited slip in the back and open in the front so really 4x4 means 3 wheels with power at one time on mine

 

The only way you get true 4 wheel drive is if you have lockers on both axles.

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No, not really.

An open differential will apply equal torque to both wheels at all times. A locker locks the shafts together permitting MUCH more torque to be applied to one side than the other. So with open differentials you are sending power to all four wheels.

When one wheel loses traction the other wheel is limited to the amount of tractive force the slipping wheel is giving. So if one wheel is on ice, you might as well have the other on an identical patch of ice.

 

Or, own a welder like me.

 

Huh?


When the axle shafts are "locked" together you have equal torque to both. Be it a locker or a spool doing the locking. I just sold a jeep with spools in both ends. That's true 4 wheel drive, all 4 tires spin the same speed whether one, two or even 3 lose traction.

 

You're not understanding this correctly.


Think about it for a second. If you lock both axle shafts together you are forcing the two wheels to turn the same speed. What if one is on ice and the other is on pavement? The one on ice will break traction at a very low torque, but the other won't. But they are forced to stay at the same speed. So the one on ice will only receive a fraction of the torque and the other will receive the remainder. That is NOT equal.

I'd love to type out a more thorough explanation, but this is much better illustrated than typed. So check out this video:

 

When you go around a corner, the outside wheel HAS to turn faster because it has a farther distance to travel. Thats just physics. A locker on the front will cause you to need a 40 acre field to turn around.

 

Tom, thanks for the video !

Not that I REALLY care - I mean - I just want it to work and since I don't design it, just getting me out of the stuck position is all I care about

So, while that young whipper snapper was logical and I followed it after the initial assumption of the formula for Force = mu*NormalForce....

if I were really interested, I'd have to go back to the proof of that initial formula to make sure it was a valid assumption

 

I'm not getting in a pissing match on this. Math is math and real world is real world.


Real world open diff operation, is that when one wheel loses traction, forward momentum is ceased. The wheel on solid ground will just sit there idle, while, yes the one on say, ice, will get all the torque. Math says that's great, but you're stuck, and that's not so good.


When you lock both axles together, they will both turn at the same speed regardless of traction. There will be more torque (or stress) on the axle of the wheel that has traction, and less on the wheel without traction, but they still turn the same speed and now you're not stuck, because the wheel that has traction is still turning.


You can give me all the math in the world, I actively 4 wheeled for 7 years, and you go further with lockers, period. No, you can't turn with them engaged, I know that. Yes they are harsh and have their place. Ford doesn't offer electric locking rears on the new trucks for no reason, lockers work, and they work better than a limited slip or open diff. The only way to turn my Jeep with spools tight was to disengage the rear axle, stand on the brakes and "dig" around the corner with the front.

 

You misunderstand my intent Scott. I'm familiar with limited slip and lockers, and I've used the more than a few times. My point was simply that torque is equally split in an open diff, but not when they are locked together. And yes, you'll go a lot farther with a locked diff than an open for the reasons stated above.

So yeah, I agree with you. No pissing match required.

 

Nope, torque is APPLIED to the axles by the power source, in this case the engine, and with a locker it is applied equally to both axles. a locker does NOT permit more torque to applied to one axle over the other, a locker is not sophisticated enough to do this. if you are trying to say that one axle is seeing more stress due to more friction (traction), then this is true, but a locker does not transfer more torque to one axle over another.

 

Watch the video below the post you quoted. If you applied the same torque to each axle shaft and one has greater resistance than the other they would be going different speeds. You can't have that happen if they are locked together.

 

I have limited slips in my '03 F250 4x4 and they BLOW. I've been stuck on dry grass before (backing up a slight grade). I'll go with lockers next year after recovering from lift and tire/wheels purchase this year.

 

No. The factory limited slip blows. As the super duty gained popularity as a daily driver vehicle and soccer mom mobile ford received complaints about how it drove, being to harsh and all. So they watered things down. The factory trac-loc was better in older trucks then it is in the newer models, also why the newer trucks (08+) require air bags if you're going to use them as work vehicles or tow because the spring rates they used to use were to stiff for many of the people that drove then to the store and back. Limited slips have their purpose, and a good one like the detroit tru-trac will perform very closely to a locker on the straights in most cases without the harsh effects of having a locker on the road