4WD , AWD, or FWD?

[Joe Russell]

While in my newly acquired 2016 explorer on a slight gravel grade my LF & RR are spinning, my dealer tells me all is well. He tells me normally the LF pulls the vehicle & the RR adds power if needed. The service writer brought the technician up to explain. He tells me only the LF & RR could possible ever be powered. I ask the service writer why Ford felt it necessary to put a CV joint on the RF front wheel that could never receive power. He could not answer. He seemed to get upset as he seemed to run out of answers. Rest assured my car will never be in the care custody & control on that dealership! I have found another Ford store I feel I can trust & will take my business there. I am hoping to learn exactly what the 4WD that is really an All WD is designed to do????????????????

 

[SuperGreg]

Looking at how the system is designed, I do wonder exactly how the whole thing works. The way the PTU works, it appears to only receive power if the front right wheel is receiving power through the diff. I would assume if the front left is spinning then the AWD system would apply braking power to the wheel to direct power to the rest of the wheels. Then the rear diff must have some clutches for power flow to the rear wheels. Is that correct? If so it doesn't seem like the best system.

 

[peterk9]

Welcome to the Forum Joe.
The 5th gen Explorer is basically FWD biased vehicle with AWD capabilities. I believe the 4WD terminology incorporates the ability to use the Terrain Management System (TMS) to select different options. I think that 'Sand' mode comes closest to locking in all 4 wheels. If you bring up the Intelligent 4WD Display you will see that upon a hard start, power is sent to all 4 wheels. There is a thread in the Forum that discusses the various terminologies as well. Haven't found it yet.

Peter

 

[KayGee]

If you bring up the Intelligent 4WD Display you will see that upon a hard start, power is sent to all 4 wheels.

At least on both of my Pius, power is sent to all 4 wheels under pretty much any form of acceleration, not just hard start. As you attain a "cruising" speed, the system mostly dials back power to just the fronts. Are the retail units really only awd under hard start?

 

[blwnsmoke]

At least on both of my Pius, power is sent to all 4 wheels under pretty much any form of acceleration, not just hard start. As you attain a "cruising" speed, the system mostly dials back power to just the fronts. Are the retail units really only awd under hard start?

In Normal mode yes it is primarily fwd. If you put the 4wd system on the dash display, you can see when the tires send power to the rears. Playing with the terrain management alters how much power and when it goes to the rear.

I know PIUs are programmed more aggressively so you may see more of an even split.

 

[jhu8]

At least on both of my Pius, power is sent to all 4 wheels under pretty much any form of acceleration, not just hard start. As you attain a "cruising" speed, the system mostly dials back power to just the fronts. Are the retail units really only awd under hard start?

Yeah my regular explorer is the same. No matter how slow or fast I accelerate from a start, all 4 wheels receive power. As you said, after a cruising speed is found it switches to fwd.

It's a nice feature but I wish it was fwd more for easy starts. Probably would get better mpg.

 

[blwnsmoke]

Yeah my regular explorer is the same. No matter how slow or fast I accelerate from a start, all 4 wheels receive power. As you said, after a cruising speed is found it switches to fwd.

It's a nice feature but I wish it was fwd more for easy starts. Probably would get better mpg.

My 11 was never like that, had to almost hammer it to see power transfer to the rear

 

[Joe Russell]

Welcome to the Forum Joe.
The 5th gen Explorer is basically FWD biased vehicle with AWD capabilities. I believe the 4WD terminology incorporates the ability to use the Terrain Management System (TMS) to select different options. I think that 'Sand' mode comes closest to locking in all 4 wheels. If you bring up the Intelligent 4WD Display you will see that upon a hard start, power is sent to all 4 wheels. There is a thread in the Forum that discusses the various terminologies as well. Haven't found it yet.

Peter

Thanks, Peter, If you find the thread discussing 4 WD on the Explorer please point me toward it. I feel I can get better answers here than from my dealer. When going up a slight grade on gravel the stuck w/ the LF & RR spinning my dealer cannot tell me why the car did not move. I feel the computer should have said: "two wheels spinning, better send power to another one & stop one of the spinning wheels". Nothing happened, the car would not move. I have been driving Grand Cherokees. I think I should have stayed there, I know what it will do.

 

[SuperGreg]

What AWD mode were you in? Street?

 

[DelcoGary]

Most 4x4 and AWD vehicles are actually 2 wheel drive (one front and one rear) unless they have a limited slip differential(s) in which case they could be 3 or 4 wheel drive. With the electronic controls, it is possible now to "brake" a wheel to help with traction and slip but power will usually only be sent to one front and one rear wheel. Your dealer wasn't necessarily leading you astray, but wasn't giving you a complete answer. I'm still learning about the Terrain Management System in the Explorer so some settings may "lock" the PTU output and send some power to the rear axle. Even so, I would think without a limited slip back there, only one side would apply much power.

I recall many years ago when our work truck - Chevy Blazer (you know, a classic one with the removable half roof, capable of going off road) got stuck and was only spinning one front and one rear wheel no matter what. Took a tow truck to extricate that one!

 

[KayGee]

Most 4x4 and AWD vehicles are actually 2 wheel drive (one front and one rear) unless they have a limited slip differential(s) in which case they could be 3 or 4 wheel drive. With the electronic controls, it is possible now to "brake" a wheel to help with traction and slip but power will usually only be sent to one front and one rear wheel. Your dealer wasn't necessarily leading you astray, but wasn't giving you a complete answer. I'm still learning about the Terrain Management System in the Explorer so some settings may "lock" the PTU output and send some power to the rear axle. Even so, I would think without a limited slip back there, only one side would apply much power.

I recall many years ago when our work truck - Chevy Blazer (you know, a classic one with the removable half roof, capable of going off road) got stuck and was only spinning one front and one rear wheel no matter what. Took a tow truck to extricate that one!

Not sure what you are talking about, but an axle with an open diff provides equal torque to both wheels. When there is a traction imbalance, the wheel with the least traction may spin, but that doesn't mean it's a 1 wheel drive.

Further, there is no way to lock or unlock the ptu output. The explorer has a permanently engaged ptu at the front and an rdu at the rear with an electromagnetic clutch pack.

 

[blwnsmoke]

Not sure what you are talking about, but an axle with an open diff provides equal torque to both wheels. When there is a traction imbalance, the wheel with the least traction may spin, but that doesn't mean it's a 1 wheel drive.

Further, there is no way to lock or unlock the ptu output. The explorer has a permanently engaged ptu at the front and an rdu at the rear with an electromagnetic clutch pack.

Forgive me lack of knowledge regarding differentials. I though an open diff gives equal power as long as both wheels have traction. And when one wheel slips, all power is going there. You need a limited slip to be able to provide some power to the non slipping wheel if 1 wheel is spinning freely.

Am I wrong?

Ps- all I can think of is My Cousin Vinney.

 

[Ironworker40]

There was a video made by Ford someone posted on here explaining how the terrain and antilock brake system work together. I can not find it. According to Ford it is capable of sending power to any wheel. It is supposed to sense which wheels are spinning and redirect power. Maybe someone else can find the video.
And yes on an open dif classic 4wd system if one wheel spins all the power goes to that wheel. If you used the parking brake sometimes you could get the other rear wheel to get power but most parking brakes did not work correctly.

 

[peterk9]

I don't understand the rationale of sending all power to a wheel with no traction (spinning).

Peter

 

[peterk9]

Thanks, Peter, If you find the thread discussing 4 WD on the Explorer please point me toward it..............

True 4wd? Or awd?

Peter

 

[SuperGreg]

I don't understand the rationale of sending all power to a wheel with no traction (spinning).

Peter

That's just the way a differential works. Anything other than that is accomplished through extra tech to limit slipping like viscous clutches, brakes applied to spinning wheels, etc.

 

[KayGee]

Forgive me lack of knowledge regarding differentials. I though an open diff gives equal power as long as both wheels have traction. And when one wheel slips, all power is going there. You need a limited slip to be able to provide some power to the non slipping wheel if 1 wheel is spinning freely.

Am I wrong?

Ps- all I can think of is My Cousin Vinney.

That's basically what I said. Torque is split evenly and provided to both wheels, but power is dependent on traction. For those saying a 2wd vehicle with an open differential is one wheel drive, or a 4wd vehicle with open diffs is two wheel drive, that is just stupid.

Here is an old movie that explains how a diff works. -> How Does A Differential Work?

For a little more info. -> Types of Differential and How They Work

Open Differential

The disadvantage of this type is that because the torque is split evenly between both wheels, the amount of power able to be transmitted through the wheels is limited by the wheel with the lowest amount of grip.

Once the traction limit of both wheels combined is reached, the wheel with the lowest amount of traction will begin to spin – reducing that limit even further as there is even less resistance from the already spinning wheel.

Manufacturers have been moving to using the brakes and other things to control traction for the majority of their vehicles, instead of opting for a more expensive LSD or torsen/active/torque vectoring differential.

 

[DelcoGary]

That's basically what I said. Torque is split evenly and provided to both wheels, but power is dependent on traction. For those saying a 2wd vehicle with an open differential is one wheel drive, or a 4wd vehicle with open diffs is two wheel drive, that is just stupid.

Here is an old movie that explains how a diff works. -> How Does A Differential Work?

For a little more info. -> Types of Differential and How They Work

Open Differential

The disadvantage of this type is that because the torque is split evenly between both wheels, the amount of power able to be transmitted through the wheels is limited by the wheel with the lowest amount of grip.

Once the traction limit of both wheels combined is reached, the wheel with the lowest amount of traction will begin to spin – reducing that limit even further as there is even less resistance from the already spinning wheel.

Manufacturers have been moving to using the brakes and other things to control traction for the majority of their vehicles, instead of opting for a more expensive LSD or torsen/active/torque vectoring differential.

No need to call people stupid because they have an incorrect understanding. We're here to learn and help the community.

 

[KayGee]

No need to call people stupid because they have an incorrect understanding. We're here to learn and help the community.

No one called you stupid. I said that saying a 2wd vehicle is one wheel drive is stupid.

There's a difference between "you are stupid" and "that is a stupid thing to do/say".

 

[Joe Russell]

What AWD mode were you in? Street?

What AWD mode were you in? Street?

I went thru all modes......same result!