Toyota 4WD systems explained

heatwave3 · March 2002

wwest: you state "The Sequoia is implemented using 3 open diff'l and 3 "dog-clutches". In 2WD mode it is RWD. If the FWD dog-clutch(1) is engaged it allocates torque amongst the four wheels by modulating the brakes, braking a(ny) wheel that slips or the computer deems is beginning to slip."

I agree with the description, however unlike the H-1 Hummer which has a similar electronic system similar to the Sequoia's, there is no Torsen limited slip differential which the Hummer has. Consequently, the torque in the Sequoia will go to the rear of the car through its open differentials until it is forced forward by the system sensing slippage, braking 1 or both rear wheels and then forcing torque to the front through the open diffs.

While the technology is different, the principle is the same. Slip, react, transfer, grip.

AWD is grip, slip, react, transfer and increase grip. That's why all the sophisticated sensing in the world will not replace having the grip in the first place.

wwest · March 2002

Assuming the F/R final drive ratios are the same equal torque will initially be delivered to ALL four wheels until enough torque is reached to cause A(NY) wheel to "slip", and then, only then, will brake modulation begin to apportion torque.

pschreck · March 2002

Did you receive the Sequoia shop manuals that you ordered? Thanks.

heatwave3 · March 2002

wwest: I think you'll find the torque distribution will be the same as other auto 4wd systems that have limited slip diffs and an open diff in the front. Namely that all the torque goes to the rear wheels as the vehicle is driven against the resistance of the air and road. Similar to the way the GM and Ford systems have all the torque on the rear wheels until slippage.

Instead of using a limited slip diff or viscous coupling that solidifies to transfer power, the Sequoia system instead grabs a brake disk wherever slippage occurs and forces it across the open diffs to a corner where its not slipping.

Curious that if Sequoia delivered equal power to all four corners unless slippage occurred they would certainly promote that fact. I still believe the absence of any torque distribution data on the Sequoia system places it into the same category as other full-time 4wd systems that transfer torque but don't provide any torque distribution data because it remains a 0/100% fr/rear until needed and then its transferred.

I would be very open to any data which would clarify the matter.

wwest · March 2002

If the Sequoia has three open diff'l, and I'm sure it does, how/why would it favor routing torque to the rear vs the front in 4WD mode.

Unless is does have differing drive ratios F/R, something I simply don't know.

It was the owners manuals I ordered and yes they did come in, finally. Dealer shipped the first set to another west.

pschreck · March 2002

wwest makes a valid point. If there are three open diffs, what would limit the torque to the rear wheels only?

cliffy1 · March 2002

What do you believe would happen to a Land Cruiser on your little test?

heatwave3 · March 2002

I'll be the first to admit I can't explain the physics behind the issue. I do know that in an open differential rear, which is the case in every rear wheel car (and every front wheel drive car) without a limited slip diff, all the power goes to one wheel. In essence, in a open diff setup you actually only have 1 wheel drive. If you were to take a car with an open diff and rev the engine hard enough to spin the wheels you would only have one "burn out rubber" mark on the road.

Posi-diffs were the next step in forcing the power to both rear tires. Limited slips were the next stage of development to disperse the torque mechanically.

The Sequoia seeks to bypass the mechnaical linkage in favor of electronic braking to prevent a tire from slipping and in essence force the torque across the drive shaft, and through the open diff to a wheel thats not slipping.

My question is, if you could rev the engine hard enough would all four tires leave "burn-out" marks on the road? I don't know the answer, but in order to understand the traction of the Sequoia under normal road conditions, you have to know the amount of torque designated under dry conditions. Its my contention, that in the absence of data suggesting otherwise the electronic system in the Sequoia preserves all the torque on the rear tires unless traction is lost. Then it is transferred forward.

If that were not the case, its also my contention that Toyota would have called their system AWD which they have not.

cliffy: describe the Land Cruiser system for me again and I'll give my spin on it

dielectric7bb · March 2002

open diffs, at least the ones at the front and or rear, operate by splitting torque 50/50. Yes if you try and light the tires up, only one will spin. This is because static friction if higher than kinetic friction. A wheel slipping with respect to ground has kinetic friction. So once one wheel breaks loose, the power sent to it is limited by a lower coefficient of friction. LSD's can send more power to one side over the other. Lockers keep the speed of both equal.

A link on open diffs:

http://www.howstuffworks.com/differential5.htm

wwest · March 2002

During startup, acceleration, weight shift is toward the rear. So if I were an engineer designing an AWD I would probably bias the engine torque to the read by adjusting the final drive ratio. 50/50 torque "bias" would likely result in a front wheel braking loose first, not exactly a desireable situation.

dielectric7bb · March 2002

During acceleration weight is shifted off of the front tires and over the rear (whether it is rwd, fwd, or awd/4wd). This is why super unlimited funny cars at the strip are rear wheel drive vehicles (they have anti-tip bars on the rear to keep the front wheels just barely off the ground so they don't send the front wheels over the top). 50/50 torque "bias" may result in a front wheel breaking loose first, but this is dependent upon acceleration and weight distribution although on average you are correct. So one may want a 60/40 or a 40/60 split, but it all depends upon the vehicle and the situation it is being driven in.

heatwave3 · March 2002

dielectric: That is a very good site. They also have an excellent description of 4wd systems <http://www.howstuffworks.com/four-wheel-drive.htm>.

You'll find that in their description they have a thorough description of how the Hummer system works and its advantages. You should note that the significant difference between the Hummer Electronic Traction 4wd system and the Sequoia system, is the lack of Torsen Diffs in the Sequoia.

I think after reading their description you'll have better understanding of why I believe the Sequoia system is a very "reactive" system due to its open diffs combined with electronic traction control.

The grinding noises and loud pump sounds are the reaction of the electronic traction control and transfer of torque due to slippage sensed by the system. Had there been Torsen diffs in the Sequoia, the likelihood of torque transfer would have been greatly reduced and the need for much of the unusual sounds coming from the Sequoia's 4wd system would have only occurred under extreme slippage.

As it is currently designed, open diffs will result in slippage and reaction more frequently than in a system w/o open diffs.

An awd system will typically be designed to deliver a dedicated amount of torque to the front and rear wheels under all circumstances, thereby reducing the need to transfer torque under all but extreme differences between the front and rear traction.

That's why I have asked if the Sequoia system is designed with a pre-set minimum amount of torque to each end. Most of the load in a vehicle that is accelerating is at the rear of the vehicle as it "pushes" the vehicle forward, thats why its my belief that the torque is "driven" to the rear of the vehicle unless slippage occurs.

I have no source to conclusively support this view. Its just my opinion and also based on the absence of data from Toyota that would clarify the matter by providing minimum torque distribution ratios.

cliffy1 · March 2002

So, you say the only difference between the Hummer and Sequoia is the presence of torsen differentials right? So, how does that affect the front to rear power distribution? Torsens are only present front and rear, not center.

dielectric7bb · March 2002

with 3 open diffs the system should work like this w/o any interference from braking (electronics).

the center open diff splits engine torque 50/50 front to rear.

the rear open diff gets 50% of engine torque and splits it 50/50 so the left rear and right rear each receive 25% of the engine torque.

the front open diff gets 50% of engine torque and splits it 50/50 so the left rear and right rear each receive 25% of the engine torque.

So each wheel is actually getting 25% of the power at all times with open diffs. Whether or not the electronic system is working or not, each axle (front left, front right, back left, back right) is receiving 25%. Now the brakes are at the end of the axle and can stop torque from going through the wheel, rubber, and to the ground. Each axle is then limited to 25%, but if the electronic system senses slippage, each tire/ground contact can be varied %wise.

heatwave3 · March 2002

cliffy: I thought according to your extensive knowledge of all 4wd systems that the Hummer has 3 open differentials, just like the Sequoia's?

Yes, the Hummer has an open differential when set for operating on roadways. However when slippery or off-road conditions are encountered the Hummer can be locked at its center differential.

You seem to still be missing the point of my views on awd. The Hummer will clearly be a better off-road vehicle with Torsen diffs combined with an electronic traction control than your typical awd system. However, it is hardly the epitome of "on-road" handling which is the condition most people that buy a Sequoia will be operating in.

A viscous liquid center coupling is a desirable compromise in a 4wd vehicle where its road-handling capabilities are more important that its off-road capabilities. By having a Visc liq ctr diff you can commit some torque to the front end under all conditions, enabling the ability to transfer more if needed while at the same time ensuring the vehicle's driveability at all speeds and on dry road conditions.

The only way the Hummer can achieve its off-road capabilities is with a locking center diff combined with rear and front torsen diffs. The only way this same vehicle can be operated on dry roadways at normal highway speeds is with an center diff which can be set to "open".

The Sequoia offers neither the off-road locking capabilities of the Hummer or its torsen diffs to balance torque, nor does it offer the "guaranteed" minimum torque to both the front and rear of the vehicle as an awd vehicle does for on road performance.

The Sequoia is probably a better vehicle for Off-road purposes than a vehicle that is awd with a visc liq ctr diff, but only under the most rigorous of off-road conditions which is hardly likely for most Sequoia owners. OTOH where it will be used most, is on road surfaces that may or may not be slippery.

Under those circumstances, its my opinion, that the tt4 system with 3 open diffs in the Sequoia, will not delivery as good a traction output as an awd system utilizing a LSD in the rear and a visc liq coupling in the center.

I think this is a very fair statement based on the very knowledgable engineers that have concluded the AWD system I just described is the foundation for some of the best performing AWD vehicles from the highest quality manufacturers from around the world. I'm sure you're not suggesting all these manufacturer's are mistaken because Toyota took a different path in designing the Toyota.

wwest · March 2002

The Sequoia system is likely the best all around because the need to apportion and re-apportion, and etc, torque can be virtually instantaneous.

Agreed, with three open diff'l 25% of the engine torque is delivered to each of the four wheels. Right up until the available torque exceeds the traction coefficient of any wheel or wheels, then ALL of the available torque will be routed to the wheel or wheels with the LEAST traction.

Show me an LSD that doesn't need a few turns of "wind-up" (its two output shafts turning at differing rates) to become active and we'll go patent the sucker and make millions.

The Sequoia's VSC/TRAC/ABS computer can (without attesting that I know it actually does....) detect a "pending" traction loss condition on any wheel or wheels and instantly react to modulate the brakes accordingly.

The VC takes hundreds of milliseconds of its two sets of clutch plates turning at disparate rates before the heating of the fluid causes it to thicken enough to increase the torque coupling.

xman1035 · March 2002

I am planning to buy a 2002 4x4SR5 V8 with ABS andLSD or a 4x2 Tundra V8 XCab with ABS, LSD and off road package plus other options. From all my readings on this thread the Tundra 4x4 systems is different from what is on the Sequoia and Land Cruiser.

My off road driving will be mostly trails and the beach about 3-4 times a year. I live in Southern California.

I wanted to know that since Toyota now offers a LSD on the 4x4 and 4x2 has it changed the 4WD system on the 2002 Tundra.

I have also read that the 4WD system on the Tundra can't be used on dry pavement and will damage the transfer case, while the Sequoias and Land Cruisers can with no damage. Too bad Toyota did not put the same 4WD system used on the SEQ and LC on the Tundra.

I appreciate your opinions.

dielectric7bb · March 2002

3 open diffs:

'Right up until the available torque exceeds the traction coefficient of any wheel or wheels, then ALL of the available torque will be routed to the wheel or wheels with the LEAST traction.'

That's the way it looks, but not the way it works. The open diff is a 50/50 split, no matter what (in theory anyway, sometimes they are more like 60/40 or vise versa dependent upon internal friction and other problems). When one wheel spins, the available torque is still split at 25/25/25/25, but torque to each wheel is now limited to the least amount of traction of that slipping tire. A slipping tire doesn't take very much torque to keep it slipping though, so it appears that all energy is going to that one tire, while it isn't.

pschreck · March 2002

I have heard that the Active TRAC system will be on future Tundras. Oh what a happy day that will be for pickup buyers.

pschreck · March 2002

Try calling Toyota at 800-331-4331. They will be more than happy to answer your questions regarding the Sequoia and it's fantastic Active TRAC system.

gpm5 · March 2002

I have driven the sequoia this winter on the freeway up steep mountain passes in the snow. At 65 mph there is no slippage or fishtailing of the rear, and there are no noises at all. The only time there is ABS pump noise is when you mash the accelerator from a stop or at slow speeds when on a snow covered road.

wwest · March 2002

100Hp engine, three open diff'ls, one wheel raised off the ground, (or on ice, mud hole, etc.)its spinning only dissipates 25%(?) of the HP yet the vehicle doesn't move, where is the other 75% being dissipated?

dielectric7bb · March 2002

What makes the engine develop 100 horses??? if the wheel spinning one let's say ice gets 5 ft-lbs of torque, then every other wheel is limited to 5 ft-lbs of torque (assuming 3 perfect open diffs). The engine can rev and it's power will go into rotational inertia, heat, noise...and those tires.

gpm5 · March 2002

If the spinning is not stopped as in the sequoia system then all torque goes to zero or something close to it. No friction=no torque. Its like racing your engine in neutral.

dielectric7bb · March 2002

yes

it's like racing your engine in neutral

heatwave3 · March 2002

wwest: I think one point you are not seeing in the differences between awd and 4wd is the dedication of torque in awd vs making torque available in a part time 4wd system. This is the principle difference between a 4wd system and an awd system.

The awd system with limited slip diffs and visc liq diffs can be designed to provide a minimum % of torque to a wheel under all conditions whether there is ice, gravel or dry pavement. No such minimum can be assured with the open diffs and tt4 traction system of a Sequoia.

Imagine the following scenario. Your vehicle is placed with all 4 tires on very slick ice at a standstill. In an awd vehicle, I know that in the case of the Denali 38% of the torque will be delivered to the front wheels and 62% will be delivered to the rear and because of the limited slip diff in the rear and the viscous center coupling.

I am assured that the tires will rotate even though they might spin. The vehicle will certainly move forward as it builds momentum.

I truly have no idea how the Sequoia will respond, however in a vehicle with open diffs the engineering would suggest the tires will not move. If they don't rotate the TT4 system has nothing to measure and no benefit is gained by braking a wheel thats not rotating. Exactly how is that a better traction system than one that guarantees power to all 4 wheels under all circumstances?

cliffy1 · March 2002

Your question seems to have been lost in a haze of misinformation. In answer to your question, the Tundra is a conventional part time 4WD system that can not be used on dry pavement without damage. Believe me, I wish the Tundra came with the Active-Trac system. My lease expires in December and I am crossing my fingers that it will be available by then. Until then, the LSD rear will help traction, but not nearly to the extent that the Active-Trac will.

cliffy1 · March 2002

Why do you even bother? You're embarrassing yourself. Where did you ever come up with the idea that the Sequoia comes with a viscous coupling center?

wwest · March 2002

was 100HP, ignore it.

I was simply, and only, addressing the issue of AWD/4WD(?) using three open diff'ls, I'm not in the least pretending that such a configuration actually exists.

dielectric7bb · March 2002

I understand, but say an engine makes x amount of power. With no wheels slipping and 3 open diffs, each wheel gets .25*x. With one wheel slipping and only able to handle a*x, each wheel is then only receiving a*x. So the total power to the ground is now 4*a*x. This just doesn't change. The engine may be able to produce more than 4*a*x, but it won't be able to for very long. Very rapidly the engine will redline and fuel will be shut-off (if no fuel cut-off then the engine will just blow-up).

eagle63 · March 2002

"AWD is grip, slip, react, transfer and increase grip. That's why all the sophisticated sensing in the world will not replace having the grip in the first place. "

-That's actually what I like about part-time 4wd. 50/50 torque split no matter what. no sensors, no guessing. In deep snow it can't be beat.

heatwave3 · March 2002

cliffy: you state "Why do you even bother? You're embarrassing yourself. Where did you ever come up with the idea that the Sequoia comes with a viscous coupling center?"

Maybe you might want to get off that pedestal of knowing everything. I certainly don't claim to know everything there is to know about 4wd systems but I've owned a variety of different 4wd vehicles and have what I consider a pretty extensive experience of 20 years operating them.

You've claimed to know alot of information which might be well respected by many people unfamiliar with how these systems work. I've respected your views and the information you have provided, however you have been inaccurate on several occasions regarding some pretty basic info readily available on the net.

Instead of feeling compelled to respond to me with your sighs and indignation, you might want to consider simply getting your information right instead of speculating or assuming information I share must automatically be wrong because I drive a GM.

Now to answer your question. Please go back and reread my posts. I've never claimed that the Sequoia has a liq ctr diff. In fact I've stated clearly on various posts that the system has 3 open diffs. (which is one of the weaknesses of Toyota's approach to 4wd IMO).

I did state that the Land Cruiser which you claimed has the exact same 4wd drivetrain as the Sequoia, in fact, is not the same as the Sequoia. I provided a source (above) which states that the ctr diff on a LC is a viscous liquid locking ctr diff. I also pointed out that the overseas models have a locking rear diff which is also lacking in the Sequoia. No where did I claim the Sequoia has a "viscous ctr coupling".

heatwave3 · March 2002

eagle63: what you fail to understand is that the Sequoia cannot deliver "50/50 torque split no matter what. no sensors".

You fail to understand the nature of open diffs even with traction control. There was an excellent site provided earlier which can better explain why, but basically your Sequoia will sense slipping in the front tires (for example) and potential move all the torque to the rear wheels. The system IS sensing this slippage and IS moving the torque throughout the open diff system until it finds a wheel that's not slipping. What I would like to know is how the system handles traction if all wheels are slipping as on ice. Open diffs will act as if the vehicle was placed in neutral with the engine accelerating but no power is transferred to the wheels.

The Sequoia does not and cannot deliver 50/50 distribution of torque to both ends at all times. If you don't believe me ask cliffy since he appears to be the only information source that Sequoia owners will believe.

wwest · March 2002

"Sequoia will sense slipping in the front wheels (for example) and potential move all the torque to the rear wheels"

NO !!

The Sequoia system will apply the brakes to the slipping wheel(s) (front, in your example)allowing the engine torque to remain elevated and the torque distribution will therefore remain approximately "equal", at least that is the "target" (equal rotational rate for all four wheels) for the ecu firmware.

If all four wheels are (persistently) slipping the only solution for that is a tow chain.

eagle63 · March 2002

"eagle63: what you fail to understand is that the Sequoia cannot deliver "50/50 torque split no matter what. no sensors".
You fail to understand the nature of open diffs even with traction control. There was an excellent site provided earlier which can better explain why, but basically your Sequoia will sense slipping in the front tires (for example) and potential move all the torque to the rear wheels."

-I don't own a Sequoia and couldn't care less what kind of 4WD system it has. I'm talking about plain vanilla part-time 4wd.

heatwave3 · March 2002

eagle63: Now I getcha. I thought you were referring to the Sequoia's 4wd system when you made your comments about sensors and 4wd systems.

Yes, there is the advantage of simplicity and "forced torque" through a part-time 4wd system. The major downside however is the inability to use the system on dry pavement. You give up the advantage of the extra traction in turns and the simplicity of not having to activate 4wd should the roads suddenly turn nasty.

That's why so many manufacturer's are trying different designs to come up with the maximum traction of 4wd combined with useability of use on all road types.

heatwave3 · March 2002

wwest: you don't appear to understand your own drivetrain and its advantages and liabilities. Think through you post once again

"The Sequoia system will apply the brakes to the slipping wheel(s) (front, in your example)allowing the engine torque to remain elevated and the torque distribution will therefore remain approximately "equal", at least that is the "target" (equal rotational rate for all four wheels) for the ecu firmware."

Your own post tells you that what your saying is inaccurate. When the TT4 system determines that a front wheel for example is slipping, it automatically brakes that wheel to slow or stop its rotation. By doing so, it automatically drives the torque away from that wheel. In fact it can brake that wheel until all torque previously going to that corner has been re-distributed elsewhere. It does not, in fact, "maintain" the torque at that wheel as you state. It does exactly the opposite.

It will continue to brake wheels until it finds a wheel or wheels that can actually use the torque without slipping. It does not do anything to maintain a 50/50 split of torque.

If the front wheels are slipping on ice for example there will be no torque delivered to the front wheels. There is no target torque distribution the ECU is trying to maintain as the system does not measurement of torque. It fact it doesn't care what the torque is. It only measures slippage or impending slippage and then attempts to prevent it from occurring by grabbing the brake on that wheel.

If all 4wheels are slipping, 3 open diffs will act as if the vehicle is in neutral, with the engine disengaged from the tires. In contrast, an awd vehicle will rotate the tires, possibly slipping but moving forward nevertheless, as it builds momentum the slippage will be reduced and the vehicle will move forward.

pschreck · March 2002

How can a vehicle gain momentum if all four wheels are slipping? If there is any traction to gain momentum with, then the wheels aren't truly slipping. And if a AWD vehicle has enough traction to move forward why wouldn't the full-time 4WD vehicle have enough traction to move forward?

wwest · March 2002

wwest · March 2002

There is no need for an LSD on the GS300, nor ANY lexus with TRAC. For a RWD vehicle as long as both rear wheels have a reasonably close or equal, level of traction, the open diff'l will deliver equal torque to both rear wheels.

TRAC only comes into play if one rear wheel begins to slip and then TRAC will instantly apply, release, apply, release, etc, the brake to that wheel, using the on/off cycling of the brake to modulate the frictional coefficient of that wheel such that it's rotational rate roughly equals that of the opposite wheel.

If this condition persists for more than a few hundred milliseconds and the operator does not react quickly and lift the throttle then the TRAC ecu will itself dethrottle the engine.

The Sequoia, ML, and I think the new LC, AWD systems work the same way except TRAC will use the brakes on any wheel or wheel to alleviate wheelspin.

Three open diff'ls with TRAC to insure true AWD operation on most surfaces, dry, slippery, snow, ice, etc.

The Sequoia only locks the center diff'l in L4 and with the transmission shifter in "low", otherwise it uses TRAC to apportion torque in AWD mode if slippery conditions are encountered.

tidester · March 2002

If there is any traction to gain momentum with, then the wheels aren't truly slipping.

Not true! Just because the wheels are slipping doesn't mean friction has been reduced to zero.

tidester
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pschreck · March 2002

I believe that's what I was trying to say. My point being that if the AWD vehicle can find some traction then why can't the full-time 4WD find traction? If a tire sticks to the ground even for a fraction of a revolution, you should move. Isn't that a function of the tire as long as the wheel is turning?

tidester · March 2002

Got ya! I thought you meant something a little different.

tidester
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heatwave3 · March 2002

pschreck: There are unusual circumstances where it is beneficial to turn traction control off. The reason all traction control system can be turned off is because under icey or snowy conditions, from a standstill, it can be advantageous to spin the wheels to generate some forward momentum that a traction control system would prevent from occurring.

In fact, I suspect your owner's manual will probably reference these circumstances and provide the recommendation to turn of the traction system in order to "rock" the vehicle out of a stuck situation or in an effort to spin your wheels to move slightly forward until greater traction is achieved. These are not common situations but they do occur.

An open diff (w/o the traction system engaged) would aggravate the situation since the ability to spin the tire will be exaggerated as all the power of the engine is direct to one wheel through the open diff. With an LSD, both tires would spin providing a greater chance for some forward momentum to be realized.

With the traction system engaged and an open diff, it would be impossible to force the tires to rotate if they are slipping. I see this as a potential problem in a wet, boggy or icey traction situation (of course at that point you could then engage a system like the Toyota's into the part time mode which would force the power to the tires by locking the ctr diff.)

wwest: your description above is somewhat accurate, however it misses on several points. While the GS does not NEED the LSD because of the traction system, it would be a better handling and faster accelerating car with the LSD combined with the traction system. It would also provide greater traction and flexibility in icy conditions for the reasons I just described above. That's why the highest performance vehicles combine LSD diffs and traction control.

Secondly, you are wrong on the following statement "AWD systems work the same way except TRAC will use the brakes on any wheel or wheel to alleviate wheelspin."

AWD systems "ensure" that torque is delivered to a wheel. TRAC only prevents the available torque at a wheel from causing it to spin. These are two entirely different principles. The trak system on a Sequoia is focussed on preventing slippage w/o caring about whether power is actually delivered to the wheel. All AWD systems primarily are focussed on first ensuring power is delivered and then secondarily, through the liq visc ctr diff and LSD, transferring it to wheels that aren't slipping.

That's why its my belief that a Sequoia with all its wheels on ice might very well just sit there, with no tire rotation whatsoever even though the engine was accelerating.

For the record, I did hear back from Toyota today in answer to the question I asked "When the Sequoia is operating in full-time 4wd what is the distribution of power from front to rear in % of torque on dry road surfaces? Your assistance would be greatly appreciated."

Their answer was
"We apologize for our delayed response to your email.

When the 2001 Sequoia is operating in full-time four-wheel drive mode, the amount of power distributed varies, as it is determined by the traction. However, the maximum percentage of power distributed among the front and the rear in part-time four-wheel drive mode, with the center differential locked is 50/50."

From this reply it would appear that the max torque distribution is not 50/50 when in full time 4wd and only when in part-time with the ctr diff locked.

I have sent a follow-up question for better understanding the Sequoia's system
"Regarding the response provided to me below on the Sequoia 4wd system below, I would like some further explanation to better understand its operation. Specifically, I would like to know what the minimum % of torque (if any) that is designated to the front wheels when placed in full-time 4wd mode and when the system is being operated on dry roadways? Or does the system direct all the power to the rear wheels and only transfer power to the front wheels when its needed due to slippery conditions?

Thank you in advance for your reply to this email to help me better understand how the full-time 4wd system functions."

I will share the reply when its been received.

wwest · March 2002

heatwave3

Can you tell me of any vehicle with all four wheels slipping on ice that would move forward better then any other?

Even 2WD?

If all four wheels are slipping on an icy surface you need MORE TRACTION!

Tire chains or...

A tow chain!

And either of these will work just as well with a 2WD.

heatwave3 · March 2002

wwest: to answer you question "Can you tell me of any vehicle with all four wheels slipping on ice that would move forward better then any other?"

Yes an awd vehicle with studded tires:)

No seriously. I would say an AWD system with mechanical diff that distribute power and have minimum torque levels to each corner, combined with a traction system that prevents wheel slippage and possibly an electronic engine controller that reduces engine output in order to better match power to traction. I might even argue that on completely flat slick ice, I would want to turn off the traction control just at the start of going from a standstill to moving and rely on the engine management and and drivetrain delivering power to all four wheels. Once I was rolling I would definitely then want the traction control activated.

oswalt1 · March 2002

I've a 2002 Sequoia and have been following the discussion in hopes of a definitive answer on whether I can leave it in 4wd all the time. I like how it handles better, etc. in this mode so this appeals to me. I did take a second to call Toyota, and after a brief consultation with a technical specialist, their rep told me that it should not be left in 4wd all the time, but rather this should only be used when needed. So, logic and all you guys say it can be left in, I'd like to leave it in (but don't want to risk damaging the drivetrain of my new $45K ride), but Toyota says don't. If I don't, then I have to put up with 4WD that doesn't engage immediately when I need it - that little flashing light will be annoying then because I'm probably stuck or close to being stuck). Clearly, the old style lever in my Durrango had its advantages. Is there any way to definitively resolve whether I can leave in in 4hi all the time?

cliffy1 · March 2002

Here is an interesting link for some of you. This comes courtesy of Piasan via pscheck (I think). http://isuzu-suvs.com/ Scroll to the bottom and click in the Sequoia info. You will need Acrobat Reader to view it.

cliffy1 · March 2002

I gotta tell you, I've never had a tremendous amount of faith in the guys at the consumer service 800 number. You may want to call them back and ask the following questions in this order:

1. Do both the Land Cruiser and Sequoia operate off the Active-Trac system?

2. Is the Land Cruiser always in 4WD?

3. Is there any damage to the drive system of the LC by being left in 4WD all the time?

4. If the systems operate in the same manner when engaged, why would it not be safe to use the Sequoia in 4WD all the time as well?

My guess is that you'll hear a pause, followed by "ummm" followed by, "Well, I'm not sure. I'll have to get back to you on this." At which point, the "technical" guy will actually call somebody at engineering and find out that you can. He will then try to figure out a face saving way to inform you of this.

wwest · March 2002

My copy of YOUR owners manual says the 4WD drive mode can be used at all time but suggests better gas mileage would be obtained in 2WD mode.

On reading the manual it appears that to be safe you should never put the transmission shifter in "low" position. The manual is unclear about whether or not the center diff'l would get locked in this mode, so the safe thing to do is avoid the possibility.

The manual is quite clear that in 4lo and with the shifter in the "low" position and the transmission is actually in low gear the center diff'l will be/get locked.

Toyota 4WD systems explained

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