4WD Questions

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.

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

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.

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...

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.

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

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

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?

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.

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.