Hey all,

I have been asked by many people on other forums to explain the 4wd system of the '01-'02 4Runners 4x4 (also similar on '03 4Runner V6 models...see below). I just bought a '02 Limited 4x4, so i did some research and off-road testing on my new 4Runner.

Here is my take on it: (please correct any of it)

The 4Runner uses a 4-wheel-ABS-based traction control, called ActiveTrac (ATRAC for short). ATRAC is ALWAYS on, even in 2WD mode where it works on the rear axle.

Here are the different features of the 4Runner's 4wd system: (VSC is vehicle stability control)

(Note: read below for more info on HOW to engage the different modes)

1. 2WD mode: Rear wheel drive; switch to 4WD up to 62 mph.

2. 4WD HI: 4WD on any surface (full-time!), however, VSC is STILL active...thus, if you get stuck bad or climb a hill & slip, engine power will be cut because of VSC's inherent functions.

3. 4WD LO: 4WD with torque multiplication (2.57 times)...again, VSC is active. (read below on how to go to 4-LO)

4. 4WD HI with center diff LOCK: same as #2 but VSC is OFF, thus allowing you to spin your tires to get out.

5. 4WD LO with center diff LOCK: same as #3, but with VSC off.

To go from 2WD to 4WD HI, you push the 4WD button on the side of the transfer case lever, up to speeds of 62 mph. After pushing it, you are in 4HI and can go up to top speed on dry land with no damage.

To go from 4HI to 4LO, you need to stop the 4Runner...shift to NEUTRAL, then switch/push the transfer case lever to 4LO. Then, you put the transmission back into DRIVE.

To LOCK the center differential (thus, TRUE 50/50 power split between front and rear axle), you need to push the button to the left of the steering wheel on dash. This should be done only on loose terrain (because of 50/50 split) to prevent binding of the center differential. Again, this will disable the VSC, allowing you to power through mud (which you cannot do effectively if VSC is ON).

In reality, the MAIN reason most people LOCK the center diff in the 4Runner is to turn OFF VSC. Very few off-roaders (esp. beginners) will ever see the need of the true 50/50% split. An example is if BOTH your front (or rear) wheels or 3 wheels are in mud (no traction)...in which case, locking the center diff is a good thing because it allows 50% of power to be routed to the AXLE that still has the wheel(s) with traction. Without the center diff LOCK, 100% power will be routed to the axle that has both wheels slipping (thus, you are stuck). However, this is rarely encountered in off-roading.

SUMMARY:
1. 4runner ('01-up) has 4-channel ABS system
2. It has VSC (stability control) and ATRAC (4-wheel traction control)
3. No rear locker
4. You can switch into 4wd (4-HI) at any speed up to 62 mph
5. You can drive in 4wd all day long at any speed
6. You can switch from 4wd to 2wd at any speed
7. But you do NOT want to lock the center diff on dry pavement...this is ONLY done off-road or on slippery ground.
8. Locking the center diff shuts off VSC (stability control), which is a good thing in off-roading. VSC tends to kill momentum when you're slipping & sliding and this is not desired in off-roading (under most circumstances)
9. ATRAC is always ON. In 2wd mode, it works on your rear axle. In 4wd mode, it works on front and rear axles
10. So, you have several modes: 2wd...4-HI...4-HI center diff LOCK...4-LO...4-LO center diff LOCK.

---------------
For 2003 and up, V6 & V8 4Runners have a Torsen center diff (Torsen T-3 design) that is lockable (true 50/50 split). V8 model has full-time system (no 2wd mode). V6 model has an additional option of 2WD. It is basically a full-time system that varies torque transfer to the front and rear axle according to amount of slippage. Prior to 2003, the torque split was 50/50% most of the time (center diff unlock). I believe the Torsen provides more stable handling (due to torque variations) in slippery conditions. The above description applies for 2003 4Runners with V6 4wd system.

The 2003-up V8 models have a full-time 4wd system similar to Toyota Land Cruiser, Lexus LX470, and GX470. With this system, the 4runner is ALWAYS in 4wd Hi mode (center diff can be locked or unlocked). There is also a 4-LO range.

Hope this helps.

Hey all,

To further clarify above:

1. Once you are in 4HI, you are in FULL-TIME 4wd. This is why the 4Runner's 4wd system is so great...so darn flexible! Remember the MULTI-MODE 4WD system is still the same as those found on pre'01 models...it is indeed FULL-TIME once in 4wd. IN FACT, you can leave the 4Runner in 4wd FOREVER! This is something you could NOT do in pre-'99 models (before multi-mode 4wd).

2. With the incorporation of the ATRAC, there was NO need for the rear Toyota electric locker (available on 4Runners prior to 2001). Why do you need it?? ATRAC provides pseudo-limited-slip differential for front AND rear axles.

ATRAC is equally effective as any limited-slip differential. However, it is not as effective as a pure locker.

ATRAC actually does NOT transfer torque side to side as explained by Toyota brochure...it PREVENTS one wheel from losing total power. Let's look at one axle only.

If one wheel is on ice and the other is on dry land, then the wheel on ice will spin. The wheel on dry land will have no power. Why?? Well, power/torque flows to the wheel with the LEAST resistance...thus, it flows to the wheel on ice. Ok, so what does ATRAC do?? ATRAC uses ABS sensors and looks at the speed differences between the two wheels. Since the wheel on ice is spinning faster than the other wheel, ATRAC applies braking power to that wheel...slowing it down to the same speed as the other wheel (THAT is it's goal). By doing so, you are increasing resistance to the spinning wheel...thus, allowing engine power to now flow equally to the other wheel (since both wheels have equal resistance). Thus, in theory, the maximum power one wheel gets is 50%...never 100%. Thus, it prevents the wheel with traction (dry land) from losing power.

For more info on ATRAC, please see:

http://www.toyota-4runner.org/showth...&threadid=5036

3. When off-roading in rough terrain or mud, you need to LOCK the center diff because it turns OFF VSC. Because, if you are stuck in mud, VSC may interpret your attempts to get out as oversteer/understeer (especially if you are sliding back and forth). Therefore, it WILL cut power (dethrottle). With VSC off, ATRAC can function with full engine power to get you out. Thus, you can spin all four wheels! I have seen this on my brother's Lexus LX470 and Discovery. THAT IS WHY YOU LOCK THE CENTER DIFF, among other reasons!

4. You can be in 4LO and not have your center diff locked. Again, this may be pointless in some situation (crawling, etc.), but great for towing (as stated above).

And best of all, ATRAC is active all the time...on dry land, rain, snow, mud...any surfaces!

For 4th gen 4runners, please see this thread:

http://www.toyota-4runner.org/showth...?threadid=2388

Thanks.

Here is a good discussion on VSC with video: http://www.toyota-4runner.org/showth...548#post213548

Thai,

I thought I saw the official specs of the '01/'02 system once, but haven't been able to find it lately. However, on the '03 specs, power will be given up to 53% front and 70% rear if there's slippage, a far cry from 100% that dual lockers could provide to a given wheel. Here's the main quote from this article which is in the middle of the page.

"It applies a rear bias in four-wheel-drive mode, splitting torque 40/60 front-to-rear in normal driving conditions, providing the driver with a traditional feel and better stability when accelerating. The 4WD mode may be used in all types of driving conditions on all types of roads, from dry pavement to wet or snow-covered roads. The system gives the 4Runner a sure-footed feel because power is applied to all four wheels, improving traction. When the front wheels slip, up to 70 percent of the power goes to the rear wheels. When the rear wheels slip, up to 53 percent of the power goes to the front wheels."

As it also states, it is a 40/60 split in 4WD, not 50/50. Just an FYI to pass along and a good read/review on the '03's.

I would have to think the above stats would be very similar if not identical to ours. Dang it! I want to know for sure!

Later,
D

Darren,

The 3rd gen 4Runner 4wd system (since 1999) has a 50/50 split all the time (when you engage 4wd). It does not vary. I suspect that when you turn around a corner, the system "gives" allowing for different wheel speed between the front and rear axles. This system is similar to Torsen T-2 system.

The Torsen system (T-3 design in 4th gen 4runners) is better than ours ONLY in handling at high speed where a rear bias of torque is preferred. For example, that is why BMW X5 sends more torque to the rear wheels, instead of 50/50. Same goes for most 4x4 sports car. This is to promote gradual oversteer, rather than understeer, which is important in handling.

However, for a 5000+ lbs of steel that is high off the ground, i don't see much benefit in the rear bias Torsen system. Maybe with the new '03 4Runners, Toyota is envisioning a more sporty truck. It is also a great advertising proclamation: "4Runner is the first SUV in it's class to have the Torsen center differential."

The Torsen does NOT help in off-roading. In off-roading, you would lock the center diff, which will then distribute torque 50/50.

The A-TRAC system is the equivalent of having Limited-Slip Differential front AND rear axles. It is not going to be as efficient as an aftermarket locker system front and rear (aka. Detroit's) over severe terrain (rock climbing, deep mud). But, then again, with ATRAC, you don't have to worry about turning the lockers on and off while off-roading.

For more information on the '02 4Runner, try this thread:

http://www.toyota-4runner.org/showth...?s=&threadid=4

Thanks.

Am I correct that the new V8 4-Runner has full-time 4wd standard and the V6 has the part-time 4wd (like 3rd generation).

Also the V8 has the same tow capacity as the V6 (5,000 lbs)?

Gas tank has been upgraded to 23 gallons.

Personally I like the V6

Eric,

Remember that the "part-time" system on the V6 models has a FULL-TIME 4wd setting too!

Yes, with the integrated hitch, it can tow 5000 lbs. HOWEVER, in the GX470 brochure, it clearly states that with the OPTIONAL hitch (avail early next year), it can tow 6500 lbs. I assume this is going to be bolt-on hitch, like those found in the old 4runners and Land cruisers. In addition, i assume that this will also apply for the '03 4Runner.

Hope this helps.

Hey Thai,

Have you found any information showing the torque bias specs for our multi-mode center differential? I'm curious as to what the torque split would be for the front and rear using the planetary type center differential.

Thai - that for the reply, but my concern is driving in full-time 4wd all the time, including dry roads with the new V8 4runner. I'm old school (at 39 years of age), driving all the time must increase maintenace on the drive system, pending some slip designed into the system by the Toy engineers. Tires must wear more too, don't you think.

Personally, I like to throw the lever or push the button when I need it. Always been taught to go in 4wd before conditions warrant it.

For that, I'm leaning toward the V6. And I agree, the torsion diff doen't do much.

What your thoughts?

Eric,

Well, drivetrain wear MAY increase if you use full-time 4wd. However, this system has been out for a long time...and i know of NO report of any type of failure or premature wear & tear. The center diff being GEAR-based helps a lot in keeping maintenance to a bare minimum.

Tire wear will actually be more even if you use full-time setting...you may not even need to rotate according to some owners!

Fuel economy is the main reason to avoid getting full-time 4wd. But from EPA ratings, there is little difference between V6 and V8.

Hope this helps.

Thai -

The key thing is that everyone should look at their needs and wants.

For us, the V6 made more sense -- the part-time 4WD and improved economy (albeit small, it does add up over time) is helpful when you look at the driving we will be doing. For example, the only time we expect to tow a trailer is to Home Depot when we need plywood or mulch -- certainly not a strain on the V6.

On the other hand, if you're serious about off-roading, towing, etc., there is probably no better choice than the V8. It gets reasonably good gas mileage, but the forums indicate a wide variance in what people really get with the engine (hence the term, YMMV).

That's obviously why they have the different options. It would have been perfect, though, if they had offered the V6 with the 5 speed transmission. (But as they say, wish in one hand and crap in the other, see which one fills up first... )

Now we are counting the days till we join the list of happy 2003 owners.

Some people have questioned me: "Why do you need to lock the center differential when Torsen is already full-time??"

If you lock the center diff, you have 50/50 split of power front-to-rear. This also turns off VSC (stability control...aka dethrottling). This will allow the 4-wheel traction control system to manage left-right distribution of power in front and rear axles via applying braking power to slipping wheels. Because VSC is OFF, the engine does NOT dethrottle when slipping in mud, which would be bad.

Front and rear differential are ALWAYS OPEN. Traction control manages the side to side transfer of power.

Torsen center diff is very similar to Torsen rear differential found on many modified off-roading rigs. The most famous aftermarket rear Torsen diff is, Detroit Truetrac. It is GEAR-based (a good thing). On a Torsen REAR differential, if one wheel is completely spinning, the OTHER wheel on the same axle will be powerless (no torque)... Torsen is excellent in all conditions short of this. In such a situation, you need to apply some braking power to get power to the wheel with traction...a common practice among off-roaders is to either apply brake via brake pedal or slowly pull up the e-brake.

Well, the same thing can happen (in theory) to a TORSEN CENTER diff (as seen on Toyota 4Runners and Range Rovers). If the whole rear (or front) axle on the '03 4Runner is completely in deep mud (no traction), then there is a chance that the other axle (in this case, front) will NOT get any power (even thou it is full-time). For these rare situations, the Toyota Torsen center diff is LOCKABLE. In such rare instances, if you lock the center diff, which guarantees 50/50 power split (front-rear), you will not have any problem getting out. One of the beauty of the Toyota Torsen center diff. By locking this, you also disable both VSC (stability control) AND dethrottling feature; thus, allowing you to power out of a mud hole.

This is similar in principle to the rear differential found on the new Jeep Wrangler Rubicon. The Rubicon has a Torsen LSD AND an air locker on the rear axle. Cool stuff!

Torsen diffs are VERY reliable and very quick-acting. It is quicker acting than most other LSD. It is gear-based, so maintenance is very low.

Hope this helps.

Why do you need to lock the center differential (CDL):

1: ATRAC requires a certain minimal wheel rotation speed to work. If you are moving very slowly, it won't do much. Backing slowly down a steep hill is one scenario where ATRAC does not work well.

2: If you have an electrical failure that takes out the system, or take a stick in a wheel sensor harness, you are stuck. With a CDL you can regain much of the lost traction.

3: If you break a driveshaft U joint, you are stuck - your rig will go nowhere under its own power. With CDL you can lock the center diff, remove the offending shaft, and attempt to drive out of the woods.

4: If you want to add limited slip or locking diffs in the axles for improved low speed traction (see #1) then they won't be effective without a CDL.

5: ATRAC is hard on the brakes and the differential spider gears. A CDL helps by reducing the workload on the ATRAC.

Great information, Thai!!

Regarding the V8 mileage with full-time 4WD I am seeing very pleasing results so far.

I drive 70 miles a day to and from work(highway) and do regular 150m+ road trips. Since I live in downtown DC I also get a dose of city driving on the weekends.

I've just passed the 500 mile mark with my blue baby and if her computer is correct I'm averaging 20.5 MPG. Not bad for a muscular V8, eh?

Gonna be fun when I get my first foul-weather/offroad day...

At the dealership, I was told a few things that I wasn't sure about, but after reading this thread, I'm really suspicious. I have an '02 by the way.

1) He said that in 4WD HI, I shouldn't drive over 55mph or I would do damage.

2) When locking the diff, I should stay under 10mph for it to work properly or again, I would do damage.

I've locked my diff to get unstuck a number of times. I know the skid control should be automatically turned off - but completely? There were a few occasions in deeper muddy terrain that I still felt the VSC working and the indicator light was flashing. (I was in 4WD LO, with the diff locked) Could there be something wrong with the system or should VSC still function on a limited basis even with the diff locked?