AWD VS 4WD

[Josh B]

What are the advantages of AWD over 4WD or vice versa?

I have 4WD on the Ranger that is fairly locked in once engaged, which to me is the main purpose for it.

I also got an AWD with the Explorer but it never seemed to work that I know of, and the transmission blew a seal before I got to mess around with the AWD so I know next to nothing about it from actual experience

 

[don4331]

The difference between 4WD and AWD is AWD has some form of center (as in internal to transfer case) differential.

So, AWD is fine to leave engaged on hard surfaces (pavement) as the differential will allow differences in tire size, turns, etc to be compensated. The disadvantage of AWD, if 1 wheel has zero traction, all the power goes to that wheel and you go nowhere.

4WD rigidly connections from and rear axles, so at least 2 wheels always have power. The disadvantage - the drivetrain will bind on hard surfaces due to differences in tire size, turns, etc.

Note: Tires are not identical even if same size due to manufacturing tolerance, air pressure in tire, weight on tire, heat from sun, etc.

 

[Josh B]

" AWD has some form of center differential." , don't all drive axles have a center differential?

 

[rusty ol ranger]

" AWD has some form of center differential." , don't all drive axles have a center differential?

AWD has a diff in the transfercase so it doesnt bind and can be used on dry surfaces.

However, AWD usually doesnt have a low range, and is generally fully automatic with no input needed from the driver.

On a regular 4wd the driver has to turn a knob, yank a lever, or push a button to engage the front tires, AWD senses traction lost in the primary drive tires and automatically sends power to the other wheels.

Also real 4wd systems split power evenly 50/50 between both axles, AWD doesnt.

However lines can be blurred, like in the case of my jeep. It has center diff action like awd, but gives a power split of 49/51, and powers like that 100% of the time. It also has low range that gives a 50/50 split, and thru the different terrian modes can change the amount of center diff lockup.

 

[superj]

i never had problems with the awd system i had on a grand cherokee back in the day. they called it something else but the t-case was always in one setting, whether it was the awd version or if i put it in 4-lo.

i later swapped to a normal wrangler t-case, thinking maybe i could get a little better gas mileage but it didn't change. all it did was let me smoke the tires where it wouldn't do it before

 

[sgtsandman]

Other than the above mentioned differences, AWD tends to not be built as robustly as a 4X4 drivetrain. 4X4 is expected to take more abuse and be used off the improved/maintained roads. AWD is expected to not see worse than a gravel road or maybe very mild off road driving. Stress the word “expected”. I’ve found AWD to be surprisingly capable as long as you stick to somewhat maintained fire roads and the like.

 

[rusty ol ranger]

i never had problems with the awd system i had on a grand cherokee back in the day. they called it something else but the t-case was always in one setting, whether it was the awd version or if i put it in 4-lo.

i later swapped to a normal wrangler t-case, thinking maybe i could get a little better gas mileage but it didn't change. all it did was let me smoke the tires where it wouldn't do it before

Mine seems to function well in snow atleast. We had 8 inches of nasty slushy shit and even on the offbrand street tires i had zero issues.

Atleast in "snow" mode. If you leave it in auto mode it kinda likes to spin and bounce like a FWD car while still allowing the ass end to get pretty sideways before the trac control does its thing.

 

[lil_Blue_Ford]

I think the difference has been pretty well explained. I went with AWD in my green Ranger project because I intended on using it primarily as a street truck. I was also under the impression that by using it I wouldn’t have to modify my driveshafts which turned out to be incorrect for some unknown reason. But I’m not intending to off-road the green Ranger, the closest it’s likely to see is gravel roads and driving back the road in a friend’s field. I have 4x4s for going off-roading in. The green Ranger I wanted to be able to flatten the gas pedal with the 5.0 and just go without spinning tires.

 

[Josh B]

AWD has a diff in the transfercase so it doesnt bind and can be used on dry surfaces.

However, AWD usually doesnt have a low range, and is generally fully automatic with no input needed from the driver.

On a regular 4wd the driver has to turn a knob, yank a lever, or push a button to engage the front tires, AWD senses traction lost in the primary drive tires and automatically sends power to the other wheels.

Also real 4wd systems split power evenly 50/50 between both axles, AWD doesnt.

However lines can be blurred, like in the case of my jeep. It has center diff action like awd, but gives a power split of 49/51, and powers like that 100% of the time. It also has low range that gives a 50/50 split, and thru the different terrian modes can change the amount of center diff lockup.

A differential in the TC, so that would severely limit that TC's usefulness to other drivetrains eh? Like the 1354 (I think that number is correct) is adaptable to numerous other vehicles or set-ups?

I thought it had a similar switch to the 93 Ranger but not exactly, it has a 3 position 2WD/4WDhigh/4WDLow and the 93 Rangers is a simple 2 button 4WD High and 4WD Low, with lights on when engaged.

I am considering disposal options for the remains of the vehicle. I have considered the airbags being its' best asset, as a blown airbag would effectively total the vehicle, and maybe someone with a wrecked 96(ish) could use it as a shell to remanufacture their favorite ride
OR taking saving some parts and parting the others
OR just a simple swap of some sort

It has bungs all over it but they're all small but obvious, one some nut tried to raise the right front with a jack under the fender haha I can't stop from laughing there, but overall it would not be that overwhelming.
One thing about it, that thing has 10 large windows, 5 doors, and a large roof rack and not a single leak, after 28 years

One other thing about the AWD, it operates off of air pressure or vacuum somehow?

 

[don4331]

AWD has a diff in the transfercase so it doesnt bind and can be used on dry surfaces.

However, AWD usually doesnt have a low range, and is generally fully automatic with no input needed from the driver.

On a regular 4wd the driver has to turn a knob, yank a lever, or push a button to engage the front tires, AWD senses traction lost in the primary drive tires and automatically sends power to the other wheels.

Also real 4wd systems split power evenly 50/50 between both axles, AWD doesnt.

However lines can be blurred, like in the case of my jeep. It has center diff action like awd, but gives a power split of 49/51, and powers like that 100% of the time. It also has low range that gives a 50/50 split, and thru the different terrian modes can change the amount of center diff lockup.

AWD does not send power to other wheels when power is lost in primary drive tires - because it has differential in transfer case, it send the power to the tire with the least traction. Which is why my daughter's Escape with AWD can be stuck with one wheel on ice, yet the other 3 are on dry pavement.

Now, with 21st century electronics, mfrs may install an AWD transfer case, then monitor wheel speed. If wheel appears to lose traction, they take advantage of ABS system apply brake to that wheel and that causes power to go to the other wheels. Just like applying parking brake judiciously did on rear wheel vehicles with open different back in the day. The different terrain modes, control how much wheel spin is allowed before the traction control comes into effect. If traction control is done really well - e.g. BMWs, you don't even notice it is occurring.

If the transfer case in your jeep has 49/51 split in high range, if the differential is still open in low range, it still has 49/51 split there. Only if differential is locked in low range will it send power 50/50.

 

[rusty ol ranger]

Im not super familar with the ins and outs of the 1354 but i think that the 2 hi function is just there because they dumbed it down so people wouldnt think they had to have one of the buttons pushed to move? I really dont know.

AWD's have different styles of systems, mechanical, electro clutch, viscous, and pry a few others.

The older Expys and Exploders with the "A4WD" option used electro clutch.

 

[don4331]

A differential in the TC, so that would severely limit that TC's usefulness to other drivetrains eh? Like the 1354 (I think that number is correct) is adaptable to numerous other vehicles or set-ups?

I thought it had a similar switch to the 93 Ranger but not exactly, it has a 3 position 2WD/4WDhigh/4WDLow and the 93 Rangers is a simple 2 button 4WD High and 4WD Low, with lights on when engaged.

One other thing about the AWD, it operates off of air pressure or vacuum somehow?

I installed a NP242 AWD transfer case into my Ranger as part of my V8 swap. Differential in transfer case didn't limit my swapping it (actually made it more desirable)

The differential in NP242 is a helical gear one (one gear having 48 teeth and the other 52, results in the 4% bias toward rear wheel. The NP203 transfer case differential has spider gears just like your front or rear axle.

 

[rusty ol ranger]

AWD does not send power to other wheels when power is lost in primary drive tires - because it has differential in transfer case, it send the power to the tire with the least traction. Which is why my daughter's Escape with AWD can be stuck with one wheel on ice, yet the other 3 are on dry pavement.

Now, with 21st century electronics, mfrs may install an AWD transfer case, then monitor wheel speed. If wheel appears to lose traction, they take advantage of ABS system apply brake to that wheel and that causes power to go to the other wheels. Just like applying parking brake judiciously did on rear wheel vehicles with open different back in the day. The different terrain modes, control how much wheel spin is allowed before the traction control comes into effect. If traction control is done really well - e.g. BMWs, you don't even notice it is occurring

If the transfer case in your jeep has 49/51 split in high range, if the differential is still open in low range, it still has 49/51 split there. Only if differential is locked in low range will it send power 50/50.

When wheel slippage is detected it sends power to the non primary drive wheels. Otherwise AWD is worthless. They arnt capable (in general) of sending 100% torque to one wheel.

If its a FWD and the left front slips, it should send power to the back right as well untill grip is regained and then it sends it all back up front. I think most AWD runs a 70/30 split.

Only in auto is the jeeps t case fully differentiated. It can vary the degree of lock depending on terrain mode selected. In 4low it completly locks.

 

[sgtsandman]

The power slip and how the front and rear axles engage differs from vehicle to vehicle and manufacturer to manufacturer. So, it’s hard to give a definitive answer.

Subarus have a limited slip in the transfer case and, depending on the model and options, a limited slip in the front and rear axles.

Hondas either have a hydro-mechanical or electronic clutch system in the rear differential that engages when the front wheels slip a certain percentage. The rear differential supplies up to 50% of the power to the rear wheels. The rear differential is a combination of a transfer case and a differential. So the actual differential is open. The front differential is also open.

As far as what Ford uses, I’ll have to defer to those above say on how the system is setup and what it does.

I’ve been is some very icy situations with a Honda CR-V and was able to still go. It may have been in a crab while doing it but it still moved. Off road, I never had a problem but it wasn’t on true 4X4 trails either. Just poorly maintained fire roads or better. Beyond the possibility of getting stuck, it is real easy to get a permanent tweak in the unibody.

 

[don4331]

When wheel slippage is detected it sends power to the non primary drive wheels. Otherwise AWD is worthless. They arnt capable (in general) of sending 100% torque to one wheel.

If its a FWD and the left front slips, it should send power to the back right as well untill grip is regained and then it sends it all back up front. I think most AWD runs a 70/30 split.

Only in auto is the jeeps t case fully differentiated. It can vary the degree of lock depending on terrain mode selected. In 4low it completely locks.

Most (like @sgtsandman 's qualification, most, not all) AWD is FWD with clutches/viscous fluid to add in rear axle, because that is the cheap less expensive way to do it. As the rear axle is driven off the passenger's half shaft, the transmission differential "sees" 75% load on passenger's 1/2 shaft. As transmission has open differential, when you get in really bad conditions with only 25% of load on driver's side, the driver's front tire spins out. Hondas, VWs, FWD based Fords (Escapes, new Explorers), Jeep Patriot, etc all use this system.

AWD is useful because rarely does one wheel have zero (0) traction, so while is it send 97% to one wheel, it is send 1% each to the other 3 and hopefully that keeps you moving. My Ranger, with the NP242, will sit there in mud spinning both rear wheels (I have locker in rear axle) with transfer case differential open (AWD setting on transfer case). Pull it from AWD to 4WD to cage the differential and off we go. (Was rather embarrassing <2cm mud and I was going nowhere until I put it in 4WD).

The electronics, both sensing and control, are so good at this point, that mfrs want open differentials in both transfer case and axles as any mechanical override is messing the electronics.