What’s the difference between ‘4-wheel drive’ and ‘all-wheel drive?’

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maktruk

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4wd is typically (almost always, really) selectable for off/hi/lo gearing, whereas AWD is usually (again, almost always) full-time, and no selectable gearing.

4WD drivetrain consists of engine, transmission, transfer case, front and rear differentials

AWD drivetrain may or may not do away with the transfer case by integrating it into the transmission, not so much these days...

There are also other differences, consisting of how and when power is delivered to each wheel. When a vehicle turns, the inside wheel turns slower than the outside wheel. AWD generally corrects for this, in different ways on different models. Most true 4WD models will bind the axle if the road is dry pavement with no allowing for wheel slippage.

That being said, AWD is generally not acceptable for the type of wheeling we (I) like to do, but it can be acceptable in many overland situations.
 
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TreXTerra

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Here is how I think about it, and probably not technically accurate because the lines between systems have gotten fuzzy.

4WD: The key component is that power goes through a transfer case with a selectable low-range.

Full Time 4WD: This system often claims to have a "Center Diff" and has selectable low-range. Many systems also have a way to lock the center diff/transfercase to send power equally to both axles in high gear. Every system like this I've seen will lock the center in low range. High-Range acts more like an AWD system.

4WD systems tend to be more heavily built than AWD platforms.

AWD: A whole variety of systems fit this category. Most use a modified FWD chassis with a PTU to get power to the back wheels. With the exception of Subaru, most auto makers have very limited power distribution and their chassis runs in FWD unless traction is lost, then a small amount of power (max 30% in most cases). These systems do not have a low-range and are typically lightly built.

These days both categories can have very clever differentials and traction control systems, although torque vectoring differentials are usually only found on higher-end vehicles like Range Rovers and the Subaru STI. Most the other traction systems use the computer-controlled application of individual brakes combined with open diffs to force power to the desired wheel. If you check the manual for many off-road vehicles, including the Toyota 4Runner Trail, it discusses not using certain traction aids if the brakes get too hot.
 

maktruk

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You're right in that the line between the two has become fuzzy, which is why I had a difficult time explaining it. Power takeoffs are a description I was trying to convey and couldn't, so I didn't try lol
 

Mad Garden Gnome

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I like selectable / part time 4wd because, at least with a free spinning front end, you can get better mileage in RWD, vice being in AWD, having to power all wheels all the time.
 

maktruk

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I like selectable / part time 4wd because, at least with a free spinning front end, you can get better mileage in RWD, vice being in AWD, having to power all wheels all the time.
That's the thing, most current AWD models don't deliver power full time, they actually *cut* power to the wheel that slips vs. powering the wheel that doesn't.

Again, the line is so fuzzy its like a wet feral cat. The main things to remember about 4WD are:

A) Selectable gearing
B) More robust/heavy duty
C) Upgradeable! Twinstick TC's rock!
 

HangryMachinist

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Ive been to that site a lot. My transfer case only shows what type (247 J) and my badge by the shifters say Quadra Track II. I do have the Quadra Drive Badge on my tailgate but would like another way to tell. Would it be in the vin #? Im asking because I have a friend looking for a WJ. It seems like the Badge is the only tell tell sign and I find that very funny.
 

Mad Garden Gnome

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That's the thing, most current AWD models don't deliver power full time, they actually *cut* power to the wheel that slips vs. powering the wheel that doesn't.

Again, the line is so fuzzy its like a wet feral cat. The main things to remember about 4WD are:

A) Selectable gearing
B) More robust/heavy duty
C) Upgradeable! Twinstick TC's rock!
In other words, don't talk to me unless you have an Atlas II?
 

roamingtimber

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Ive been to that site a lot. My transfer case only shows what type (247 J) and my badge by the shifters say Quadra Track II. I do have the Quadra Drive Badge on my tailgate but would like another way to tell. Would it be in the vin #? Im asking because I have a friend looking for a WJ. It seems like the Badge is the only tell tell sign and I find that very funny.
I agree. I haven't found a way to tell unless you jack up the vehicle and spin the tires. Even the service manual doesn't doesn't say a way to tell.
 

roamingtimber

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I was changing to oil and rotating the tires on my WJ and figured I'd try and find something on the axles that tells you it's a vari-lok but there's nothing. The tag tells you the gear ratio but that's it. So weird.
 

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Let's see...I'm no expert here...but I believe on the landies we are full time 4wd...with a high/lo shifter....and we can pull that shifter to the left and have high/lo with locked diffs...weren't the old military jeeps full time 4wd as well?
 

WJ - Firefly

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At some point I would like to upgrade to an Atlas II. That said my shifter cover says Quadra Trac II and I have the NV 247 J. Unlocked axles until I added the Lokka lunchbox to the rear Dana 44HD. If you pull the diff cover (messy and a pain) on a variloc axle, you should be able to identify the oil pickup cups on the back of the ring gear. Plus the locker section won't look anything like spider gears...
 
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roamingtimber

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When I was rotating my tires, with one wheel off the ground, I was able to spin it enough by hand that the vari-loc kicked in and I couldn't move it any more. I was able to break torque on my lug nuts using it. From what I've read the variloc only works up to a 32" tire, after that there is too much rotational mass for it to function right. So if your friend is looking at going large than 32's it might not matter because a true locker will be in his future.