Toyota 4WD systems explained

idahodoug

I've had around 6 Toyota SUVs and 3 other make SUVs and all the Toyotas did this in low range. In actual offroad use, this works well to give you firm command of terrain. The worse the trail, the more effective this fast shift works. I've always felt Toyota used this aggressive shifting schedule in low range to minimize the heat buildup of hard high load use in the transmission (less slippage allowed during shifts means less heat).

It's extremely pronounced on the 80 series LandCruisers, but on the trail this is an asset.

IdahoDoug

hicaira

Very pronounced in my 100 series too. I think part of it is due to the high rpm shift points. Even if not under much load the 4 lo shifts are at over 3000 rpm's - 4000 if under moderate acceleration or steeply decending. This is a good 1000 rpm higher than the normal shift points in 4H.

I wouldn't have it any other way...

If that 4 runner has hill decent control it may hold upshifts till redline, btw.

HiC

wwest

Text taken from MY2002 Toyota Sequoia owner's manual, page 230, 2nd sentence of 2nd paragraph, left column. Yellow CAUTION high-lighted text.

"Be careful when accelerating, up-shifting, downshifting, or braking on a slippery surface. Sudden acceleration or engine braking, could cause the vehicle to skid or spin."

NOTE: "ENGINE BRAKING"

(DO NOT LIFT YOUR FOOT FROM THE THROTTLE QUICKLY!)

Or else quickly shift into neutral.

The Sequoia is predominantly a RWD biased vehicle, what did you suppose will happen with a FWD or AWD with front torque biasing?

Same manual, Page 143, center column yellow high-lighted CAUTION note.

"Under certain slippery road conditions, full traction of the vehicle and power against 4 wheels (4WD mode) or rear wheels (2WD mode) cannot be maintained, even though the active traction control system is in operation"

I read this statement as verification of a firmware time-out to prevent the ABS pump/motor from being over-taxed and over-heating due to continuous pump activity requirement.

This statement would likely also apply to ANY Toyota or Lexus vehicle with ACTIVE Trac and/or AWD using braking to apportion torque, HL, 4runner, GX470, RX300, RX330, Sienna, and obviously the Sequoia.

You likely have only about 45 seconds of continuous Trac or AWD "duty", then you're left with a vehicle that has 3 open diff'ls.

And obviously the ABS and VSC would now also be non-functional until the time-out expires (unless you need to do a restart cycle??) and the pump can again be activated.

pschreck

My read is: "As with all 4WD vehicles, if you are sitting with all four wheels on sheer ice, good honkin' luck."

hicaira

That's my read too. I saw nothing that said that the TRAC sys will abandon you but rather that there are limitations to the technology that cannot overcome situations where there is virtually no traction under the wheels. In such a case, I think I'd prefer a "You're on your own buddy!" than one that simply refuses to send ANY torque to ANY wheel (as the Volvo X Country I once rented did).

HiC

wwest

Driving along on packed snow and/or ice with left wheels mostly on "clear" pavement and the right intermittently so. I think we've all experienced that. Wouldn't pump quickly overheat?

idahodoug

I agree with hicaira - it's just a warning that the technology will not get you in/out of anything. I see no "verification of a firmware time out", no mention of "45 seconds" (where'd you get that?), and a vehicle with 3 open diffs will get through tough stuff just fine. Further, I see no logic in your conclusion that this means "obviously" no ABS, etc - where do you get this??

If there is a heat issue with a system splitting torque with the brakes, it will be with the rotors overheating rather than a pump. The highest potential for this to happen would be a stuck vehicle who's owner is doing nothing to help get unstuck save use his right foot (no digging, no installation of traction device, no sand, etc) and the lack of airflow to cool the rotors would be an issue. Underway, you'll have no problems - such as the 'driving along with one side on ice and the other on clear pavement' condition you mention.

IdahoDoug

pschreck

I can say that while driving the Sequoia in the snow we got in PA this year (no comparison to, say, Fargo) the ActiveTrac system rarely kicked in with braking. Whether the snow was deep or packed patches. I imagine that with tires that are more worn than mine, it might activate more often. But certainly not for 45 seconds at a time. I made a seventy mile round trip on Christmas day in a storm that rapidly dropped about a foot of snow and I doubt that I had braking action for a total of 45 seconds.

wwest

was posted somewhere here on edmunds. The Sequoia owner had gone off-road and found himself in a very muddy patch and the VSC/Trac system quit on him in the middle, he said about 30 to 45 seconds. Lexus confirmed that there is a time-out, but felt it was likely in minutes, not seconds mostly because they had not incurred an instance in their simulated off-road driving.

drmp

I don't know if this is available in 4 hi but in situations where constant slipping occurs, a lock center diff gets the job done. Other systems like viscous, tracs, or any speed sensitive locking device will quicly wear out in this situations.

intmed99

steelcruiser

You can't lock center diff in both Hi and Lo range on all LCs. The newer ones offer this as standard, but on the older ones, the diff locked when you put it in Lo range. I'm speaking of LCs and standard configurations.

idahodoug

Who "at Lexus" confirmed this timeout? I am a former Lexus HQ employee and would be interested in re-confirming it as I'm skeptical. Lexus of Bellevue, or Lexus of Seattle?

IdahoDoug

wwest

I think the name was, or something like, "mark martin", technical supervisor at customer satisfaction inquiries@lexus.com

gkatz1

No, he is a Winston Cup Nascar driver!:-)

idahodoug

wwest,

I'll see what I can find out from my buddies still there. I'm thinking the customer service guy was kind of playing along with your thoughts on the time out thing, which is one way of handling a customer who knows more than you. Methinks there may not be such a feature since there's a customer warning about stationary or 'all wheels on slick stuff' situations, but I'll let you know.

Have a good Memorial Holiday, everyone - I'm competing this weekend and will be offline.

IdahoDoug

wwest

Allan Vaughn still about?

pehanich

Has anyone driven their Rwd 4Runner in the snow this past winter? I am curious to hear how it preforms. I live in Northeast Ohio and we will occasional get a good snow storm. Does the RWD preform adequately or should I spend the extra money and buy the 4WD. Thanks for you help.

bmw323is

I've driven 2WD pick-up trucks in snow and they don't do very well. Although a pick-up is lighter on the back end than the 4Runner. After loading them with 400 pounds of sand they were a little better. You will have to decide how often and how much snow you will be driving through. Also, a factor is whether you will buy snow tires. Don't you get ice in Ohio? Twice, I got totally stuck on an icy city street with a minor incline. Embarrassing and frustrating. Swore, I'd never own another 2WD truck if I lived in the snowbelt.

I didn't have my 4Runner last winter, but I saw one here in Denver in March doing quite well after we received 47" of snow!

wwest

Don't understand why anyone would buy a RWD (only)"SUV", but a set of high quality easily installed snowchains will typically put you at the head of the on-road adverse condition AWD/4WD "class".

FWDrivers please ignore this advice.

idahodoug

Wwest,

If it's the same Vaughn (not sure about the Allen) I worked with at Lexus 11 years ago - he's one sharp cookie. Used to race motorcycles. One heck of a great and knowledgeable guy.

IdahoDoug

wwest

At the 92 LS400 lemon law trial in 93. Tell him I said hello.

nedzel

On the 03 4Runner with the V8, it comes with a full-time 4WD system that has a locking center diff. Is a limited-slip rear diff or locking rear diff available on the 4Runner (as is available on the Land Crusher and Taco)?

intmed99

No, no LSD or locker is available. 4runner and Land Cruiser now have ATRAC. ATRAC is ABS-based 4-wheel traction control. ATRAC is not as good as a true locker. However, it is considered the equivalent of having front AND rear limited-slip differential.

Land Cruisers had an option for a rear locker back in 1999. In 2000 and on, all Land Cruisers have ATRAC.

Tacoma does NOT have ATRAC...therefore, there is an option for locker.

wwest

The way I read the 4runner brochure "atrac" is the full-time AWD system but it also has a part-time (locked center diff'l??)mode in addition.

nedzel

Personally, I think I'd prefer LSDs to brake-based traction control systems.

Yes, the central torsen diff can be locked.

intmed99

ATRAC is more flexible than any LSD. For example, a gear-driven LSD (aka Torsen LSD) is useless if you have total loss of traction on one wheel across an axle. ATRAC is not limited by this.

dielectric7bb

If you have three of four wheels on ice (no traction), then the brakes have to lock them up for power to be applied to that one wheel with traction. Since the brakes are taking power away from the drive train, you may only have 25% power to that one driving wheel (If you have a center diff lock then 50% to one wheel). LSD's are not limited to this extent. They may require a little bit of user input (brake modulation...see how they train Marines to drive Hummers), but won't chew up nearly as much power. I agree that ATRAC is more flexible than an LSD system (on road), but I think true off-roaders would prefer a lockers and then an LSD system, prior to using an open diff/brake modulated system.

corancher

Some good points made about both systems here. I wonder if we ought to talk about this in terms of other systems like the stability control, too. I suspect it's easier to integrate stability control with a brake-modulated system than with lockers or even LSDs at both axles (rather than only at the center diff). The point about chewing up power in brake-modulated systems seems valid, but I suspect that available power is not usually the problem in these low-traction situations.

Obscure fact: The yaw-rate sensor for the stability control system in the 4Runner is in the console, just forward of the shift lever. Does anybody know if it's important to place this sensor near the center-of-gravity of the vehicle?

tidester

Does anybody know if it's important to place this sensor near the center-of-gravity of the vehicle?

I don't think so. The sensors measure the rate of rotation of the vehicle (angular velocity) which will be the same for any location in the vehicle. However, positioning the sensor close to the COG may inhibit mechanical vibrations which (on older sensors) tend to reduce accuracy.

tidester, host

wwest

all of these braking implemented features. Without the developement of an ABS pumpmotor combination that can replenish pressurized brake fluid none of this would be possible.

LSD vs Atrac:

With LSD the maximum engine torque is limited by the "slip limit" to the slipping wheel(s). With the atrac the engine torque is only limited by the brake (over-)heating duration.

intmed99

Then you would not have power anywhere!! That's the big weakness with aftermarket Torsen LSD! At least with ATRAC, you have 25% of power...aka, still have enough power to move.

For a true off-roader, he/she will only look at lockers. My brother has a Wrangler Rubicon, which has a Torsen-like LSD (along with air locker) in the rear axle. LSD is far from being as effective as advertise! It is ONLY for mild terrain...where ATRAC is just as effective. Thus, he usually locks his rear locker during off-roading over moderate-severe terrain.

corancher

I intended to talk about in post #1126, I just lost my train of thought in mid-post. I was thinking about the benefits and trade-offs of the different systems in different situations. It seems like the most effective systems for really serious off-roading (deep mud, rock crawling, etc.) may not be the best for on-road and more moderate off-road use. I think this is especially true for drivers like me, who haven't driven much of the really difficult off-road stuff.

The point I originally intended to make is that in the day-to-day driving world where one can encounter unexpected slick spots and not have time to configure the vehicle for them, the combination of stability control and traction control (necessarily based on ABS and not lockers or LSDs?) may be the safest and most effective choice overall. I'm guessing that's what Toyota had in mind here, rather than sacrificing the benefits of this system for a 10/10ths offroad situation. Anybody got other opinions or knowledge?

dielectric7bb

You can always apply the brakes by hand (this makes the differentials think they have traction when they don't). LSDs apply more power to the wheel that has traction and hence the following is true:
Three tires with no traction and brake power only will get brake power minus brake power to the ground (zero)
The other tire will get brake power multiplied by LSD multiplication factor minus brake power (and we're off as long as the LSD multiplication factor is greater than 1).

In terms of off roading I would prefer the following in order of which ones will handle the rough stuff the best.
1) Locker
2) LSD
3&4) Brake Modulation or auto locker

In terms of on roading I would prefer
1) Brake Modulation
2&3) LSD or auto locker
4) Locker

I would agree with corancher that Toyota designed the system (as all/most brake modulated systems) for the road as it is more predictable and more easily integrated into a skid control system. I'm not saying that brake modulated systems are horrible and won't do squat off road. I'm just saying that I would prefer an LSD over ATRAC.

nedzel

I agree with dielectric. A couple years ago I was with my hunting buddy in his 4WD Ranger. He's got an LSD in the rear. He pulled into a downhill, ice-covered driveway to turn around. He hit the gas and the wheels spun. He shifted into 4WD and still nothing. I told him to use some left-foot braking, and he easily backed out.

With LSD's, I still have the option of left-foot braking. With ATRAC or similar, I've got no option.

wwest

With three wheels fully slipping the engine could (theretically) generate 300HP and with atrac 75 of that would go to the wheel with traction. More than a few hundred milliseconds of that continuously and the brakes would be melting. But then you should have smelled the brakes on my C4 after 3 HOT laps (professional driver) at Pacific Raceway the 3rd of July.

Brake pads WELL seated now.

wwest

Seems to me that the obvious answer is that for AWD/4WD where continous use/need is desired, say for off-roading, the 4runner wins hands down. Otherwise Atrac would likely suffice.

intmed99

Sorry, i have to disagree with using the brakes to activate LSDs. First off, by using the handbrake (or brake pedal) to force LSD to work, how do you know this provides more than 25% of power???? Secondly, i have tried such a method on my brother's Rubicon (and his earlier Jeep with Torsen rear LSD)...it provides a WEAK driving force at best! It rarely worked!

dielectric7bb

check with the U.S. Army or U.S. Marines...they'll tell you how it works! What situations did it provide a WEAK driving force (were you driving and what were the road conditions?)

An LSD can apply more than 25% power without the brakes ever being applied. LSDs are designed to apply more power to the wheel with traction than the wheel without. There is a "torque bias ratio” built into the LSD (They range from 2 to 1 all the way to 5 to 1 typically). What happens is that one wheel spins on the axle and the LSD transfers mechanically more power to the wheel that is not spinning (requiring little or no brake force).

intmed99

Not all LSD's can transfer more than 25% of torque to wheel with traction.

In the case of TORSEN LSDs (most popular), if you have NO traction on one wheel, IT WILL NOT WORK AT ALL! For example, if one wheel is on ice and the other on pavement...TORSEN will NOT work at all. And applying brake/parking brake will help the Torsen but ONLY TO SOME DEGREE. And, remember, this practice requires a lot of practice! It took a few times for me to learn it. Too much brake power can take too much power away. With ATRAC, there is no learning curve. And it works when one wheel has no traction.

BTW, Hummer H1 (yes, the original one) now has the ATRAC-like system too! Land Rovers have it.

There is NO EVIDENCE to say that ATRAC is less effective than LSD's. NONE. A locker is superior to ATRAC in the rough...but not LSD.

BTW, my brother's old Jeep Wrangler had Torsen. We tried it on ice (one wheel on ice; the other on pavement). Torsen failed completely. The wheel on ice spinned endlessly. Applying brake force slowed down the spinning wheel...however, the torque transfer was not enough to move the Jeep! And i know this because i can see the wheel with traction trying to move. Now, could i have applied to much brake?? Possibly i guess.

In mud, the Torsen works well. Torsen works ONLY when there is SOME traction in the slipping wheel.

ATRAC is NOT limited by this. ATRAC is able to work in all conditions. Like i said, the ONLY thing that is better in off-roading than ATRAC is a PURE LOCKER.

Now that my brother bought the Wrangler Rubicon, he doesn't rely on the LSD...he locks the rear most of the time when off-roading. We was very disappointed in the Torsen on his old Jeep.

dielectric7bb

of the LSD is greater than 1:1 then it can apply more than 25% power (not torque) to that corner (and ALL LSDs have a torque bias ratio greater than 1:1 otherwise they are called an open diff).

Are you sure that it was an LSD (Torsen) or was it an open diff. Sounds like an open diff to me.

Anyways check with the U.S. military as to how the Hummer perform (I'm not saying it's the best off-road vehicle ever, but why don't they use ATRAC or another brake activated system if said systems are better than LSD???).

Let's just agree to disagree as without testing similarly equipped vehicles, one with a brake 4x4 system and the other LSDs, no one will ever know...

rorr

"....more than 25% power (not torque)..."

Am I the only one confused by that?

dielectric7bb

are you confused by the 25% or the power vs. torque?

intmed99

Hummer H1...the civilian Humvee uses ATRAC. I haven't checked the Army lately on what system they used. Hummer H1 used to have LSD's, but they switched to ATRAC 1-2 years ago. Again, i would love to find out what the new Humvees have in the Army.

dielectric7bb

I didn't know that. Apparently it's called the TT4.

"Equipped with a Torsen® II limited slip torque-biasing differential and a locking transfer case, the HUMMER's TT4 4-channel system provides the best mix of electronic and mechanical systems"

Could it be ATRAC and LSD combined? or is the Torsen II from the above quote the central diff (which is also lockable)?

wwest

combined make no sense at all. Provided the ABS pump/motor can operate continously LSD would be totally redundant.

Atrac and torsen center diff'l, or something of that ilk, to apportion torque, say 30/70 F/R, when off-road does make sense however.

canddmeyer

Has anyone had their Toyota w/TRAC/VSC stuck in the mud? Tell me how it does in mud. I've always had an LS differential on my vehicles & have spun my tires as necessary for traction when needed, but I've seen a few articles where people are getting stuck cuz all 4 wheels are slipping inducing TRAC & VSC to lock up the brakes killing forward momentum & stopping the vehicle in its tracks. I'm posting cuz I'm undecided on a 4Runner, Sequoia, or Tahoe as my next vehicle & I sure don't want to get stuck miles from nowhere. I'd seen a video posted on the 4Runner link awhile back, but there was a lapse in the video & I still wonder if someone was winching or tow-strapping that 4Runner so please don't post that video as a reply. Thanks. My 1st 4WD was an '86 Toyota p/u I added LSD to after I stuck it-never got stuck after that. Since then I've owned GM products, but I would like to go back to the lower maintenance Toyota.

intmed99

The center diff is Torsen (like 4runner). However, it's front and rear diff are open and uses ATRAC technology.

intmed99

I have been stuck in mud and deep sand. Let me tell you, if you are somewhat aggressive with the throttle, you can spin your tires easily! For me, it seems like ATRAC backs off when you are more aggressive with the throttle.

Also, keep in mind that in mud, all wheels are slipping...so ATRAC is not gonna interfere to a great extent because there is not much wheel speed differences.

Also, remember that most car magazine reviewers do NOT know how to switch off VSC (in 4runner, it is by locking the center diff). VSC is what kills momentum because it will dethrottle.

Most of the negative press about ATRAC comes from the Sequoia. Why?? Because to turn off VSC and lock center diff, you have to be in 1st gear AND in low range. That is very restrictive. Most authors don't know this!! So, basically, they get stuck in the Sequoia because VSC is still on.

In the 4runner, locking the center diff can be done in 4-HI or 4-LO and your tranny does NOT have to be in 1st gear. Thus, 4runner is far more flexible.

intmed99

Actually, for 2003, there is an optional Eaton rear LOCKER (electronic). As you may know, locker is theoretically compatible with ATRAC. Because when you LOCK an axle, the wheel speed between the two wheels are EQUAL...thus, ATRAC is cool with that. Anyway, i think the Hummer H1 system shuts off ATRAC in the rear axle when the locker is locked...similar to H2 system. Basically, H1 has the best of both worlds!

Here is ATRAC system on H1:
"TorqTraq 4®
The H1's Torq Trac 4® (TT4) technology continuously monitors the rotational speed of each wheel. The unique 4-channel system automatically reduces the spin on severe terrain or slippery surfaces by applying the brake to the spinning wheel, allowing the differential to redistribute torque to those wheels with traction. Equipped with a Torsen II® limited slip torque-biasing differential and a locking 2-speed transfer case, it provides an impressive mix of electronic and mechanical systems that come together to help make the H1 safe, stable, and astoundingly off-road capable."