4WD Questions

[Bruce_H_]

I plan to purchase a new tow vehicle within the next two years. At the present time, I am towing a 3500 lb travel trailer with a 2006 Honda Pilot 4WD. The 4WD is Honda's name; actually, it is AWD with 80% front axle preference, and 4WD is only selectable in 1st or 2nd gear, and under 18 mph. However, the AWD feature has saved my bacon on two occasions when caught in unexpected snowstorms in mountain terrain when towing my previous trailer, a Chalet folding trailer.

Based on that experience, the new tow vehicle must have AWD or 4WD. I have researched Silverado, F150, Ram 1500 and Tundra pickups, and, frankly, I am disappointed in what I have learned about their 4WD capabilities. They are all part-time 4WD, meaning they must be in 2WD when on dry pavement, and can only be put in 4WD when the road surface is slippery enough to prevent binding. I really want something that I can put into 4WD before conditions turn bad, not after!

Am also considering full-sized SUV's. The soon-to-be-released Tahoe 4WD will be based on the Silverado and, I assume, will have the same part-time 4WD. The new Expedition will be based on the new F150--no indication so far about the kind of 4WD it will have.

The Sequoia has the ideal 4WD: selectable between 2WD and full-time 4WD, in which there is a center differential which prevents binding. It can be driven in 4WD mode on dry pavement. The problem with the Sequoia is that it is a really dated body design, and the second-row seats don't even fold flat, which is a necessity for us.

So far, I haven't found a solution to having a modern, full-sized tow vehicle with the option of full-time 4WD. Any ideas out there?

Hoping for some help here.

Thank you,

Bruce

[talonhead]

I have a '99 F250 4wd with shift on fly. I also have an H2 which is AWD/4wd, I wish it had a 2wd option as it would be better on fuel. It has hi&lo range in 4wd and rear diff-lok . They are very different animals. Not all 4wd systems are the same. Fords have locking hubs. Rams have Center Axle Disconnect (CTD) which disconnects the axles from the diff, but the axles still turn with the tires.
Something else, if it has traction control- make sure it can be turned off.

[DesertFront]

My 4wd nissan frontier can shift on the fly up to 50 mph. It has a simular, if not the same, 4wd system as the nissan full size truck Titan.
I think all the vehicles you mentioned all have a simular system with the "shift on the fly" capability

[Paul_Clancy]

wnjj wrote:

Paul Clancy wrote:

wnjj wrote:

Redsky wrote:
I used to have to get out of my truck and engage the manual hubs and get back into the truck and start down the road again and then do the same when back on dry pavement.

You can leave the hubs in on dry pavement or all year for that matter. It just costs you mileage. In the old days, some people left them in for the winter if they frequently needed 4WD.

Except if you do that you will bind or skid when turning corners on dry. Can't imagine that is good for the transfer case and front diff. Are we still talking about 4wd?

You can leave the hubs in with the transfer case in 2WD. The front axles and drive shaft will be spinning at a different speed than the rear at times but aren't connected to the rear when in 2WD. I was addressing the comment about having to get in and out to switch between 2WD and 4WD.

Got it. Haven't had manual hubs since my land cruiser in the 80s so it's been a while. That thing could goat crawl anywhere.

[pronstar]

Terryallan wrote:

All wheel drive. Is usually only 2 wheels engaged at a time. One on the front, and one on the back. Should one, or both of those wheels slip. they are instantly disengaged, and the other two are engaged. Should those slip as well. The system tries to engage the other two again. And if that don't work. The system "CAN" disengage all four.

I'd like to see a link to any AWD system that worked like that...

[wnjj]

Paul Clancy wrote:

wnjj wrote:

Redsky wrote:
I used to have to get out of my truck and engage the manual hubs and get back into the truck and start down the road again and then do the same when back on dry pavement.

You can leave the hubs in on dry pavement or all year for that matter. It just costs you mileage. In the old days, some people left them in for the winter if they frequently needed 4WD.

Except if you do that you will bind or skid when turning corners on dry. Can't imagine that is good for the transfer case and front diff. Are we still talking about 4wd?

You can leave the hubs in with the transfer case in 2WD. The front axles and drive shaft will be spinning at a different speed than the rear at times but aren't connected to the rear when in 2WD. I was addressing the comment about having to get in and out to switch between 2WD and 4WD.

[PUCampin]

Our Expedition EL has the 2H 4Auto 4H 4L positions on the selector. We use it a lot like you describe. 2H in summer, 4Auto if weather starts to get bad. 4H only off pavement if required.

The Ford Control Trac works like this

2H - Front hubs unlocked, all power sent to rear

4Auto - front hubs locked causing front driveshaft to turn. The computer monitors the rotational speeds of the front and rear driveshaft but power is still 100% to the rear. If the computer detects a difference between the driveshafts, the transfer case clutch engages and starts sending power to the front but retains the ability to slip so nobinding occurs. So considering how 4Auto operates, it is NOT AWD in the same sense a Subaru (had one, loved it) or Audi is AWD where power is sent to all wheels all the time. If you punch it you will feel a bit of slip and the a catch as the front wheels are engaged.

You CAN simply leave the selector in 4Auto if you want, many years of Explorers and some Expeditions did not even have a 2H option, only 4Auto, 4H, 4L. I had one (2004 Explorer V8) and it worked great, never had to think about it. The 2H option for the Expy was to slightly help it's dismal fuel economy.

With standard traction control and roll stability control, 4Auto may be all you ever need.

4H - Fully locks the clutch in the transfer case, locking the front and rear driveshafts together for a 50/50 torque split. Will bind up on dry pavement.

4L - Engages transfer case reduction ratio, along with locking the driveshafts. It also engages a different throttle map for the electronic throttle, making it easier to modulate (the pedal becomes less "touchy") for precise manuvering. 4L 1st gear crawl ratio is 41.06 (4.17 x 2.64 x 3.73). Not too shabby!


The GM system is functionally almost exactly the same, not sure about dodge.

We love our Expy and would not hesitate to recommend it.

Daniel

[Bruce_H_]

wilber1 wrote:
How much do you want to spend? The Audi Q7 TDI has a 6500 lb tow rating with the tow package and full time AWD.

Yes, the Audi Q7 TDI is a very desirable vehicle, but it is above our budget.

We are still leaning toward a full-sized SUV. Very much looking forward to the early Spring release of the redesigned Chevy Tahoe / GMC Yukon and the sometime-in-2014 release of the refreshed Expedition with the EcoBoost engine. With the information I have learned on this very helpful thread about Auto 4WD and various aspects of 4WD, I am now quite comfortable going with a vehicle that has the option of selecting Auto 4WD.

Many thanks to all who have participated in this thread. This 4WD newbie has learned a lot!

Bruce

[Paul_Clancy]

wnjj wrote:

Redsky wrote:
I used to have to get out of my truck and engage the manual hubs and get back into the truck and start down the road again and then do the same when back on dry pavement.

You can leave the hubs in on dry pavement or all year for that matter. It just costs you mileage. In the old days, some people left them in for the winter if they frequently needed 4WD.

Except if you do that you will bind or skid when turning corners on dry. Can't imagine that is good for the transfer case and front diff. Are we still talking about 4wd?

[wnjj]

Redsky wrote:
I used to have to get out of my truck and engage the manual hubs and get back into the truck and start down the road again and then do the same when back on dry pavement.

You can leave the hubs in on dry pavement or all year for that matter. It just costs you mileage. In the old days, some people left them in for the winter if they frequently needed 4WD.

[wilber1]

How much do you want to spend? The Audi Q7 TDI has a 6500 lb tow rating with the tow package and full time AWD. Good mileage to with the diesel.

The quattro system uses a 40/60 front/ rear torque split but will change the ratio if it senses slip.

[Redsky]

Full time 4WD was used in many trucks and SUV's in the 1980's but it fell out of favor as the gas mileage was a lot worse and they were less reliable. The more that is turning full time the more power that is needed and the more wear and tear.

Even where AWD was used as with the Audi, Jeep, and Toyota sedans it has been a very limited success and discontinued after a few years in most cases due to lack of customer interest.

The only time I have wanted full time 4WD on the highway is when I am going from dry pavement to snow covered pavement continually as it is easier than switching into and out of 4WD constantly. I sometime encounter that on Hwy 80 in the mountains around Lake Tahoe but that is about it. Anywhere else it is snow or a dirt road and 4WD stays engaged until I am on dry pavement.

I used to have to get out of my truck and engage the manual hubs and get back into the truck and start down the road again and then do the same when back on dry pavement. Then auto engaging hubs came on the scene and that was a blessing, but I still had to work a transfer case lever and watch my speed and manually shift into and out of 4WD. Now my truck and SUV both have a dial I turn to engage or disengage 4WD and I do not find that any more inconvenient than having to manually turn on the windshield wipers when it starts to rain.

[wnjj]

Terryallan wrote:
Thing is. there is a HUGE difference between real 4 wheel drive, and All wheel drive.
4 wheel drive is when all 4 wheels have power to them. And so when you turn a true 4x4. The difference in wheel speed from the inside to the outside. Binds the axle, unless one tire can slip. Needing a slippery surface to slip on. OR the trany is burned to a crisp.

All wheel drive. Is usually only 2 wheels engaged at a time. One on the front, and one on the back. Should one, or both of those wheels slip. they are instantly disengaged, and the other two are engaged. Should those slip as well. The system tries to engage the other two again. And if that don't work. The system "CAN" disengage all four. No damage done. But the vehicle won't move.
So If you are never going off road / pavement. All wheel drive is usually good enough. But in heavy snow, mud, or sand. Real 4x4 is a must.

The only difference between 4WD and AWD is the that the transfer case allows the front axle to turn faster or slower than the rear. Both have differentials on each axle to account for the difference in speed from outside to inside.

The reason 4WD binds on pavement is because the tire runout is slightly different between the front and rear or when you turn corners the front has to travel further. A differential or clutches in the transfer case of an AWD allows this to happen. A 4x4 must slip the tires to even things out.

Even 4WD with open axle differentials really only powers one front and one rear wheel. That can be changed with limited slip or lockers.

Some modern AWD & 4WD systems make use of individual wheel brakes to help direct the power to the tires with traction in effect acting like an electronic limited slip.

[ScottG]

Francesca Knowles wrote:

ScottG wrote:
All of those trucks can be put into 4WD on the fly, any time you wan't. So that's really not a factor.

Scott, Scott...you've missed the point!


O.P. wants something that can be driven in 4 wheel drive in any conditions, on dry pavement, at any speed for prolonged periods of time, yadda yadda yadda.

But only when he SHIFTS IT into 4 wheel drive. Because he doesn't want all-wheel drive, no, sir. Sometimes he wants it to be in two wheel drive so he can shift it into 4 wheel drive. On dry pavement. At any speed. Regardless of conditions/necessity etc.

Are you up to speed now? 😉

No, I think I'm in the wrong range and hopelessly stuck.

[1oldtruck]

Check out the GMC Sierra Denali. Mine is AWD with no selector knob to change it. My Jeep GC is also AWD with no selector. Sounds like what you may be looking for.