'01-'03 4wd system (A-TRAC, VSC)
 

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.

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 this thread:

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

Thanks.

VSC...what is it??
 

Vehicle Stability Control Systems
by Jim Kerr

First, there was anti-lock braking. Then came traction control systems. Stability control is the third step in electronic systems that help us control our vehicles. Almost all automobile manufacturers offer a stability control system on select models. Most of them are on cars, although trucks are quickly adding stability control to the option list.

While all systems are similar in concept, one system has important market significance. AdvanceTrac, the stability control option on the 2001 Ford Focus is the first system offered on an economy car, and it brings vehicle stability controls within the financial grasp of the majority of the buying public. AdvanceTrac is available on two of the Focus models, the economical and sporty ZX3 three-door, and the top of the line ZTS four-door sedan.

AdvanceTrac came from Ford's involvement with Formula One racing. Although active vehicle controls like AdvanceTrac are no longer used in F1 racing, their benefits are very real in everyday driving. Ford first offered AdvanceTrac in the Lincoln LS. This system, on the Focus, brings a new level of safety to small cars.

Stability control systems are especially beneficial on wet, snowy, or icy conditions, although they do offer handling benefits during emergency maneuvers on dry pavement. The design intent of stability control is to keep the vehicle going in the direction the driver is steering the car. To do this, the brakes are applied on one wheel to help steer the car in the correct direction. For example, if poor traction causes the front end of the car to slip sideways when you are going around a corner, the computer will apply the wheel brake on the inside of the corner causing the car to turn and slow down. If the back end of the car slips sideways, the brake on the outside of the corner is applied to bring the car back into line. The system works when the car starts to slide on a straight road the same as it does when turning corners.

Not all stability control systems feel the same. The difference is mainly in the computer programming. I find systems on Mercedes and Lexus cars react aggressively by reducing engine power and vehicle speed at the first instance of vehicle instability. Their emphasis is on always keeping the car in total control. Other systems, such as the Subaru Outback Vehicle Dynamic Control system, allow the vehicle to move around a bit for a more sporty feel, but as soon as the movement is too much, control is smoothly engaged. The Subaru system operation is my personal favourite. Most systems, including AdvanceTrac, fall somewhere between these two. Control is smooth and seamless.

Several inputs are required for stability control operation. The wheel speed sensors for the anti-lock brakes are used to detect wheel spin. A steering wheel position sensor is used to determine where the driver is wishing the car to go. A yaw rate sensor measures the speed at which the car is rotating around its centre, while a lateral acceleration sensor measures sideways force on the car. The AdvanceTrac computer monitors these sensors 150 times per second and can react within milliseconds to briefly apply individual brakes, retard ignition timing, and cut back on fuel delivery to keep the vehicle under control.

Stability control systems are a fantastic safety system. According to Johnny Unser, race car driver and performance driving consultant, "the yaw control is phenomenal in avoiding an accident by keeping the car pointing in the right direction, instead of getting out of control."

There is one caution about stability control. It can't overcome the laws of physics. Trying to corner at excessive speeds or driving beyond the limits of tire traction can cause the car to lose control. The stability system will help, but there is only so much it can do.

I have enjoyed driving many cars in the $35,000 and up price range that were equipped with stability control. The systems work even better than they sound. Now that stability control is available on a Ford Focus at under $22,000, I look forward to the safety benefits on even more cars.

Re: '01-'03 4wd system (A-TRAC, VSC)
 

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 :confused:

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.

'99-02 Open center differential
 

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... :rolleyes: )

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

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?

patin,

1. As long as you don't lock the center diff, you can drive in 4wd all you want at any speed. (Note: Nissan Pathfinder's AWD system IS supposedly restricted to 55-65 mph...crappy system!) Once you are in 4wd, the system is FULL-TIME, just like in the Land Cruiser/new 4runner V8/Lexus. Therefore, i have never heard of such restriction.

2. If you lock your center diff, then it is advisable to do it on SLIPPERY surfaces. However, you can drive in a STRAIGHT line all you want. The only problem is when you start to make a turn...this can cause binding in the lock center diff...over time, this will wear out the center diff gearing and cause damage. Thus, you lock the center diff ONLY when off-roading where gear binding is minimized due to slippery surfaces (dirt, gravel, mud, etc.).

3. Once you lock the center diff, your VSC is turned OFF. The reason you still see lights flashing and weird noises is because 4-WHEEL TRACTION CONTROL (ATRAC) is still operating, braking the wheel(s) that are slipping.

The faster your rev your engine, the less traction control intervenes. For example, if you're gunning up a muddy hill, then you need to be more aggressive with the gas pedal. I think that ATRAC cuts down it's braking above 2500-3500 rpms. So, you can power up the muddy hill, with all wheels spinning. ATRAC is mostly for lower speeds.

Hope this helps.

Torsen Center Differential: part 1
 

Link:

TORSEN Traction Differential T-3 (Type 3 or Type C)

TYPE 3 TRACTION DIFFERENTIAL
Zexel Torsen's new generation T-3 Traction Differential are ideally suited for center applications, dividing torque front to rear in all-wheel drive vehicles. Similar to the T-2 parallel axis differential, the T-3 uses helical planetary gears which pilot on their outside diameter. The T-3, however, uses an extremely compact planetary gear configuration capable of nominal torque splits other than 50/50. The planetary nature of the design allows for a forward or rearward biased torque split.

Unlike conventional speed sensing, limited-slip differentials, TORSEN T-3 is a full-time torque-sensing, torque biasing system. Torque and differentiation are continuously managed between the front and rear axles and biased instantaneously according to variable road conditions, automatically shifting the power to the wheel with the most traction before any wheel slip can occur. There are no clutches or preload to worry about, in fact, the TORSEN T-3's patented helical planetary gearing system is designed to PERFORM FOR THE LIFE OF THE VEHICLE.

TORSEN T-3 Traction Differentials are available with a locking capability range of 20-30% and a nominal split from 65:35 and 35:65, front to rear. The T-3 can be designed to fit most transmissions or transaxles with no modifications required. In addition, it is fully compatible with ABS, Traction Control Systems, and Stability Control Systems, providing the ultimate traction management systems.
http://www.torsen.com/images/T3_1_2.jpg
http://www.torsen.com/images/T3%20conversion_2.jpg
http://www.torsen.com/images/T3%20basic18_2.jpg

Torsen Center Differential: part 2
 

MULTIFUNCTION CAPABILITIES
The TORSEN T-3 is an advanced, multi-function traction system providing continuous, uninterrupted torque output, splitting, biasing, and differentiation in one integral unit. It is always active, responding instantly to torque feedback from variable driving conditions.
http://www.torsen.com/images/bias_chart.jpg

ENHANCED PERFORMANCE
The TORSEN T-3's capability to immediately respond to variable driving conditions not only provides better traction, it also enhances the general performance of a vehicle. There is a marked improvement in total tractive effort as compared to open or speed-sensing center differential equipped vehicles. In addition, the exceptional efficiency of the T-3 allows the engine's torque to be used more effectively, delivering more horsepower to the road. The combined improvement in traction and the augmented power results in a nimble yet sure-footed vehicle that provides better handling, increased acceleration and an improved margin of safety.
http://www.torsen.com/images/T3%20evaluation3_2.jpg
http://www.torsen.com/images/T3%20basic12_2.jpg
http://www.torsen.com/images/T3twin_2_2.jpg
http://www.torsen.com/images/T3twin_3_2.jpg
http://www.torsen.com/images/T3%201-pin_2.jpg
http://www.torsen.com/images/T3%202-pin_2.jpg

LOCKING EFFECT

(FRICTION INTERFACE SURFACES)

Side Gear Thrust to Housing
Planet Gear Separation to Planet Carrier
Planet Gear Thrust to Planet Carrier
Helical Tooth Mesh

Designed for today's modern all-wheel drive vehicles, the TORSEN T-3 Traction Differential is also suited for any application where a planetary differential is desired. TORSEN T-3 advantages include helical planetary gear design allowing front or rear biased asymmetrical torque splits under normal conditions. In addition, the number of planet gears can be increased or decreased, based upon system strength requirements.

DESIGNED FOR HARD-TO-PACKAGE ALL-WHEEL DRIVE SYSTEMS
The new generation TORSEN T-3 Traction Differential provides efficient torque splitting, biasing, and differentiation for improved vehicle performance. It is specifically engineered for hard to package all-wheel drive trains and is compatible with all automatic transmission fluids. The unique (patent pending) Twin Differential configuration makes the TORSEN T-3 especially well suited for front wheel drive based applications that relied on external-mounted torque-on-demand couplings to drive the rear axle. The Twin Differential offers the most compact all-wheel drive package with the greatest strength, while providing all the traction benefits of a TORSEN differential. With the TORSEN T-3, the vehicle has true all-wheel drive, driving all the wheels all the time. This can provide optimal traction management and deliver more power to the wheels, resulting in improved vehicle stability, handling, and performance.

TORSEN T-3 IS AVAILABLE FOR ALL SPLIT AND LOCKING AFFECT REQUIREMENTS

Zexel Torsen, Inc. will custom design, engineer, test, and manufacture the TORSEN T-3 Traction Differential to meet your specific torque split and locking affect requirements. Advanced TORSEN T-3 technology is a perfect match for applications with ABS, Traction Control, and stability control/vehicle dynamics systems, providing the ultimate traction control platforms for your vehicle.

Geez Thai, I thought I might get a little bit more *detailed* technical response?? :D

That actually clears up a lot. I was paranoid all last winter about leaving it in 4WD over 55mph. I'm convinced that the guys at the dealership are not used to talking to people that are really interested in using their trucks the way they are able to be used. It's been tough getting anyone there to answer questions. I've asked several times about the 4WD system and the only thing they know is to not drive over 55 while it's engaged.

That makes sense about ATRAC still operating with the diff locked. This summer, I was in that very situation where I had to make it up a really slick hill to get back to the trail we were riding. I was fighting the traction control which I didn't feel comfortable about, but I had to get on it a little to make it. That's good to know it adjusts at higher RPMs.

Anyway, thanks for the info!

No problem.

Yeah, those Toyota salesman are useless. (To be fair, they also have to sell Corrollas, Prius, Camrys, etc.) I learned all this stuff from a lot of reading and trial-and-error. I wish they were more like the Land Rover salesman (who sales only SUVs), who at least knows something about off-roading.

FYI, the Hummer H1 (the real and ONLY Hummer) has Torsen T-2 system:

"Richard Fanco and Robert Gula of AM General talked about the development of the Hummer and described the 1999 civilian Hummer

An article in the current Motor Trend (a "Perspective" by Dan Carney) talks about skid control systems and studies that have shown how effective they are.

A few quotes: "Mercedes-Benz's research cites a 29-percent reduction in single-car accidents and a 15-percent reduction in overall crashes, thanks to stability control. Deadly high-speed wrecks were slashed 55 percent." "DEKRA Automotive Research, in Germany, found a 27-percent drop in serious loss-of-control crashes. Toyota reports a 35-percent drop in single-car crashes and a 30-percent reduction of head-on crashes in Japan."

Toyota's study was comparing accident rates of the same vehicle with and without VSC.

So just to clarify if I want to get 50-50 4x4 I would turn off VSC on my 03 V8 ? But If I run with it on all the time i'm 30% to the front..and 70% to the rear..am I correct? I have turned it off in the snow once and the VSC lite was flashing thats normal?? Little confused cause this baby dont get off road with the wife driving it ..just some snow sometimes. Please clarify

TIA

If you want 50/50 split ALL THE TIME, then you need to lock the center differential (which will also turn OFF VSC).

If you do not lock the center diff, then the Torsen will split torque on it's own. That is, in normal driving with no slippage, 70% of power will go the rear and 30% to the front. If there's slippage detected on the rear axle (either or both tires), then more power is shifted to the front wheels. And vice-versa. That's the beauty of Torsen center diff and similar differentials on Toyota since 1999.

Basically, the Torsen does allow power to ALWAYS flow to BOTH axles. The only difference is that Torsen controls the distribution of torque ("how much"). When you lock the center diff, then you basically telling Torsen to ALWAYS give 50% of power to each axle ("don't think, just do it my way"). This is helpful in off-roading when you don't want the Torsen computer to "overthink" itself or disrupt traction by shifting torque back and forth.

When you lock the center diff, the VSC light should NOT blink. Read this thread:

http://www.toyota-4runner.org/showth...s=&threadid=92

Hope this helps.

I think your reply helps...in a nutshell..VSC on center diff unlocked...VSC off center diff locked 50/50 ,in most cases the Torsen does all the thinking and you would only 50/50 if you need to override the "thinking" of the Torsen in a "offroad" situation but it not daily driving ..the wife dont do off road :p My Tundra 4x4 is either on..or off ..when you think about it its a real neat system on the 4runner... thanks for the info Thai.

Yup, you got it! :)

I heard a rumor that the Tundra and Tacoma will soon have a similar 4wd system as the 4runner/Land Cruiser...that is, it's ABS-based 4-wheel traction control system (ATRAC). It SHOULD have been this year (2004). In fact, initial literature from Toyota shows the Tacoma to have a similar system...however, it seems like Toyota is waiting another year before implementing it. Hopefully, they will use the system in 2005 for all of it's 4x4.

Here is an excellent owner's writeup on the VSC/ATRAC system on ice: (It is written by CORANCHER on the Edmunds.com forum)

Last night we got just the right kind of slick snow and ice for experimenting on a very low traction surface, so I went out shortly after midnight on local streets and a couple of big parking lots to see what I could learn. I thought I'd share my experiences here and see how they compare with those of others. First (in case you don't want to read the detail) I thought I'd list the main conclusions I came to:

1. The system is very effective, and doesn't require that the user do anything different in typical situations.

2. Traction is much better (more than twice as good) in 4WD, so if you've got a V6 (with its multimode system) I recommend you switch to 4WD at your first opportunity or just leave it there any time things might get slick.

3. Traction enhancements, especially 4WD and traction control, don't change the ultimate adhesion limits for turning and braking. Those limits on the "friction circle" remain, so technology can actually allow you to get to hazardous speeds easier/quicker than before.

And now more detail on my experiences and some speculation on the hows and whys. First, I should note that I was alone in the vehicle with no cargo, so the rear end was light. I've got a V6 so I experimented in both 2WD and 4WD modes. I was running in just a couple of inches of snow near the freezing point, and the snow would pack immediately into ice when driven on (or especially when spun on) so conditions were very slick but not what I would call extremely slick.

I started out in 2WD. Even on level streets or slight slopes it was easy to get traction control (TC) and skid control (SC) working, whether accelerating from a stop or just speeding up, and whether going straight or turning. The main clue that the system is working is the noise from the pump recharging the pressure accumulator (sounds like a chattering sound or the sound of a chain slipping on loose sprockets) and the light in the instrument cluster. The pump noise often persists for a few seconds after the system has stopped acting. Other clues are the dull thunks coming from the brakes stopping or starting wheel rotation and the feel of the system doing something unusual like braking only one side to straighten you out. If you pay attention you can also feel the dethrottling.

In general I don't think traction was very good in 2WD with no weight in back. I think the Bridgestone Duelers are ok in these conditions; no better and no worse. Most folks aren

Minor correction from above owner's experience:

Locking the center diff turns OFF VSC and dethrottling function, but it does NOT turn off traction control. Traction control is ALWAYS on...on rear axle (in 2wd mode) or on both axles (in 4wd mode).

Thai-

Correct me if I'm wrong, but Active TRAC (A-TRAC) can be disabled. The ONLY way, that I'm aware of anyway, that the A-TRAC system can be disabled is when the T-case is put in 4Lo (VSC off) AND the transmission is ALSO in Lo (1st gear.) Anything other than 4Lo/Lo (4Lo/2nd or 3rd, 4Hi/Lo) and the A-TRAC system will remain active and engage if any of the wheels begin to slip/spin.

Spinning the tires in anything other than 4Lo/Lo and you should hear the A-TRAC (ABS) system ratcheting the brake calibers trying the limit the spinning.

Two words of caution: (1)Excessive and prolonged tire spinning in anything other than 4Lo/Lo can cause the A-TRAC (ABS) system to overheat and temporarily shut down (indicated by the "TRAC OFF" light on the instrument cluster) until it cools off. Once cooled to an acceptable temp, the A-TRAC (ABS) will automatically re-engage. (2) Be careful not to over-rev the engine if you want to burn out in 4Lo/Lo. Oh yea... and hold on tight (high rpm + low torgue = lots of power).

Hillbilly,

I have not heard that you can turn off ATRAC, even in the situation you described. If this is true, then you should see "TRAC OFF" when you're in 4-LO and 1st gear, right?? From my past off-roading with my 4runner, this does NOT turn off ATRAC. For me, ATRAC is always ON. You can only manipulate VSC.

Now, on Sequoia, i think that you have to be in 4-LO and 1st gear to turn OFF VSC. This is not the case with the 4runner.

Have you tried this on your 4runner??

Can you turn it off in 2WD and regular 4WD modes?
 

I know locking the diff. will turn it off but what if I want to be in control of wheel spin on road/tarmac?

It's a good traction control system but I wouldn't describe it as fun.

Well, with your 4wd 4runner, you canNOT turn if OFF in any mode.

On 2wd 4runner models, you can turn off the traction control on the rear axle (there's a button for it).

You're stuck with it i am afraid.:(

Yeah. In my Limited 4x4 2003 4runner, VSC is always on, except when the center differential is locked.
It is VERY aggresive at limiting wheelspin in 2wd mode, but that's what happens when you put 245hp to 2 wheels. I haven't been able to get it to activate when in 4wd mode on dry roads. By distributing the power to 4 wheels, the torsen differential pretty much lets all wheels get what they can handle.
As far as driving around without VSC, I am glad it's there, the saftey features that make this truck so nice are one of the prime reasons I bought it. I wouldn't bother locking the center diff. unless going off-road where I knew conditions would be slippery (low and slow) or on road up very slippery hills, where VSC "may" halt your progress. I haven't encountered a snow covered hill the 4runner couldn't eat yet though, in normal 4wd.
On a final note, 2wd mode with the stock HT840 tires is USELESS on snow!! The truck is crippled, and darn it takes FOREVER to accelerate. 4wd is great, even with VSC.

Maybe a dumb question--- is the TORSEN standard on the 04 V8 2WD models-- I have a Limited and didn't see the TORSEN on the list of options --I mean I don't recall. Or is it an optional thing?

Thanks for your responses.

Torsen is the name for the type of center differential on the 4runner. Since ONLY 4wd 4runners have center diff, Torsen is standard on all 4wd 4runners (2003-up). 2wd models do NOT have Torsen.

Thai is right. The Torsen3 center differential is only on 4wd versions (V6 or V8).
If someone gave me the complete electrical schematic I could probably find a way to deactivate the VSC without shutting off the anti-lock brakes.

Thanks fellas --would it be beneficial for me to add a locking diff or LSD?

Well, by locking the center differential, you turn off VSC. ATRAC is still on as is ABS.

Unless you off-road a lot or use it over rough terrain, you probably don't need lockers or LSDs. Your 2wd 4runner ALREADY has traction control on the rear wheels, which provides a PSEUDO-LSD. That is, it is as effective as LSD. It is not as good as a true locker though.

Excellent work Thai!

Just a few clarificatory questions, I hope you won't mind.

My Surf has the A340F A/T transmission (don't know if it matters), can I fit a torsen center diff?

Can I fit a torsen LSD into my current differentials, front & rear?

Thanks.