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Toyota 4WD systems explained



  • ustazzafustazzaf Posts: 311
    Atleast someone understands. The only way to increase traction by shifting from high to low is if a locker kicks in when you shift down. That is the case with my Tacoma. I have to be in low for the locker to kick in, so I DO get better traction in low. Aside from that, it is all in how much gas pedal you apply. The exact same wheels will get power in high or low.
  • wwestwwest Posts: 10,706

    No, all the traction you can use already exists as a function of things like stiction of the tire surface with the roadbed, weight of the vehicle, etc. The only ways I know of to INCREASE traction readily is to add weight, sand bags, and/or studs or chains.

    What this discussion is about is how to make the best use of the traction we already have, as in distribute the engine torque over a greater contact area (locker) and/or make it easier for the driver to modulate the torque, feather the throttle, at a much lower level (granny-grunt gear ratio).

    Not by any means saying the locker didn't engage in a shift to low range, but what I've been trying to point out if that the effective "gain" of the accelerator pedal was also reduced significantly.

    In many instances the best way to get going initially is to just "ease" the throttle open ever so gently and slowly. If you happen to be driving a new Corvette that might be really difficult. The Corvette engine has so much torque at the low end it is practically impossible to "soft" start it.

    But reduce the final drive gear ratio to 100:1 and even full throttle wouldn't move the car forward fast enough for the TONS of torque now available to break traction.
  • frisinafrisina Posts: 1
    I have a 2006 Tacoma 4x4 double cab, with TRD Offroad package.

    In a previous 4wd SUV, I had several options with regard to 4wd. The first was a "Full Time" 4wd, which meant the center diff. was NOT locked, allowing to drive on dry pavement - without risk of damage.
    Next, there were the traditional 4hi and 4lo, that locked the center diff, and were only for slippery (off road) conditions.

    Now the question:
    On my Tacoma, when in 4hi, is the center differential locked? The manual indicates that it is for slippery, or wet pavement. But in my experience, wet pavement may not provide enough "slip" to operate a true 4wd system, where the center diff is locked, without risk of torquing the drive train too much.

    I hope I've explained my question well enough. Any info would be appreciated.
  • abbylouabbylou Posts: 33
    I was just wondering when operating the 4-wheel drive system, when should I dis-engage the traction button on the the left side of the dash? If I drive in occasional snow on the hwy or neighborhood, shouldn't I just push the four wheel drive button? I have heard some folks speak about dis=engaging that button?
  • benzy1benzy1 Posts: 11
    Frisina, you dont have a center differential (CD), you have a transfer case, which operates effectively like a permanently locked CD.

    Check out this very good summary.

    cliffy1, "Toyota 4WD systems explained" #4, 16 May 2001 4:00 pm

    You may want to check out the first 5 posts to this thread (authored by cliffy) to get a good understanding of the pros and cons of your (and my) tacoma 4wd system.
  • johnxyzjohnxyz Posts: 94
    Would someone please eplain or elaborate on the new FJ Cruiser with a manual tranny has full-time AWD vs. part-time AWD with an automatic transmission?

    Isn't the auto tran FJ the same as the auto tran 4Runner, which has a F/T AWD system?

    Is the FJ with auto the same as the new Rav4 with auto (so then these 2 models are different from the 4Runner with auto)? Confusing...

    Thanks alot.
  • wwestwwest Posts: 10,706
    Pardon me but....

    This does not address the Tacoma specifically but...

    No 4X4 can be operated on a high traction surface absent an "open" center diff'l of one type or another. The only difference between a "transfer case" and a center differential ("case") is that the transfer case contains both a CD and a low range gearset along with the ability to lock the center differential during times of operation on poor traction surfaces.

    There are, currently in the market, part time 4X4 systems without a "transfer case" and only an open differential that can be locked for part-time use on low traction surfaces.
  • benzy1benzy1 Posts: 11
    I have no idea of what you are tying to say here wwest...

    But yes. Since the Tacoma does not have an open center differential, then it would be detrimental to drive the car on dry pavement while 4wd is engaged.
  • 2toyotas2toyotas Posts: 104
    The FJ with a manual trans has the same transfer case as the V8 4Runner. The FJ with an auto trans has a different transfer case. It does not have a center differential in it, so it can not be used on dry pavement. It is the same transfer case used on the Tundra. Once you put it in 4WD both axles are locked together, so there will be binding around turns. The RAV4 uses a totally different type of system. For 06 it is now an On Demand AWD System. The RAV4 is primarily Front Wheel Drive until there is a need for extra traction, then a clutch near the rear differential engages the rear wheels. The major difference between the RAV4 and the FJ and 4Runner, is that the RAV4 does not have a 4LOW option.
  • ustazzafustazzaf Posts: 311
    If you are driving with the 4WD locked in while taking sharp turns on dry pavement, you may cause damage, but driving a couple miles down the highway is not going to hurt anything. I've known people to drive halfway across states in 4WD with no problem. My buddy did it with my jeep years ago, and it is still working. There was alot of snow and ice in places (Wyoming in January), but alot of dry pavement too. I would not drive more than a 1/2 mile locked in during normal driving, but in bad weather when ice MAY be present, I would not hesitate to use the 4wd I paid for.
  • fox6fox6 Posts: 3
    Is there anyway possible to tow an 04 Tacoma 4x4 with 4 wheels down. Have had several conflicting answers. foxo6
  • fox6fox6 Posts: 3
    I have anautomatic transmission Tacoma. Is there anyway possible to tow it behind motorhome with all 4 wheels down?I have been told I can put transfer case in neutral & transmission in park & stop every 2oo miles & run through the gears& this would work.Also been told will not work.Please help.Thanks fox06
  • cc124cc124 Posts: 1
    I am considering purchasing a RAV4 4WD and was wondering whether or not the 4WD feature will be enough to allow it to be drive in the sand/over sand dunes, such as ones in Carova Outerbanks North Carolina...If yes why? If no, why not? Thanks for your feedback.
  • ustazzafustazzaf Posts: 311
    I am a trailer man, so you can ignore me if you want, but throwing the truck on a trailer of a similar length will not add a whole lot of length while keeping miles off the truck and alot of piece of mind. If you put 20K on a $1200 trailer, you still have a $800 trailer that you need to spend $20 packing the wheel bearings. If you put 20K on the truck, you have to pay a whole lot more to pack the 4wd bearings, drop atleast a grand in value and you have to worry about something going wrong with something on the truck while towing, costing well over the $1200 you have invested in the trailer. An example is a wheel bearing going south. Worst case on a trailer is a new axle, hub and tire at around $300. The Toyota hub, tire and labor is going to see the better side of $1200, and that is the low side. Add a few grand and you can have an enclosed trailer that will protect the paint, windshield, and give you more secure storage.
    Just my 2 cents.
  • I have read the "Toyota 4WD Systems explained" thread in the Toyota 4Runner forum, but I am still a little confused about the differentials in the 4Runner and the RAV4.

    Here are my 4Runner questions...

    Does the 2006 / 2007 V8 4Runner have a Torsen rear differential, or a Viscous Coupling Limited Slip unit in the rear differential, or does the rear differential simply rely on the Traction Control system to accomplish slippery surface wheelspin control on the rear axle ???

    When the 2006 / 2007 V8 4Runner Torsen center differential is locked by the dashboard switch, is the Traction Control system disabled ???

    Does the Traction Control system wear out the brake pads / warp rotors at lower mileage than a vehicle without traction control ???

    How capable is the 2006 / 2007 4Runner V8 on ice and in snow ??? I have family members that often need emergent medical care. I have to be able to get to care providers regardless of weather.

    There was something mentioned about wanting to disable the traction control for situations like pulling onto a highway in the rain to avoid having it slow you down suddenly and put you at risk of getting rear-ended. Is this accomplished by a switch or pulling a fuse or some other modification ???

    Thanks in advance for any info.
  • 2toyotas2toyotas Posts: 104
    The rear has an open differential, which relies on traction control to limit wheel spin.

    When the center differential is locked the traction control system is still active.

    No. When a wheel is slipping, it doesn't take much force to brake it. My brother is pretty hard on is 04 4Runner,with 30,000 miles brakes have 75% pad left.

    Very capable. If you get really bad winters, put snow tires on in the winter and it will be unstoppable.

    I think this mainly happens on the V6 when in 2WD. It is very hard to slip a wheel in 4WD.
  • Thank you for your very detailed reply. It is very much appreciated.

    Another 3 questions, if you can answer:

    When the 4 Lo Range is activated does that automatically lock the center differential ???

    Does the Traction Control function on the front wheels also ???

    Does the Sport Model suspension hop around when driven on less than smooth highways ???

    Thanks again.
  • nedzelnedzel Posts: 787
    Note that locking the center diff turns off spin control. As previously noted, it does not turn off traction control. On road, even in moderate snow, there's no need to lock the center diff. Lock the center diff in extreme conditions. I doubt you will ever find such conditions on the road.

    It performs well in snow, but realize that the controlling factor in snow is your tires. The 4WD system will allow you to accelerate quite well in snow. But it doesn't improve braking and turning performance. The OEM Dunlops absolutely sucked in the snow -- acceleration was fine but braking and turning were completely horrible. I purchased a set of dedicated snow tires. I've driven through 1 1/2 feet of snow without a problem.

    Traction control functions on the front wheels as well.

    Concerning the ride quality, I strongly suggest that you take one on an extended test drive. The 4Runner is a truck. It drives pretty well, for a truck. It handles pretty well, for a truck. It rides pretty well, for a truck. But there is no mistaking it for anything other than a body-on-frame truck with a live rear axle. My 2003 4Runner does have a mild hobby-horsing motion on rough pavement. You can certainly feel that heavy rear axle moving around. It is not a sedan, minivan, or car-based SUV. It's big and heavy with a high center of gravity. It's cornering limits are low and when you reach them it will understeer mightily.

    I've never had a problem with the spin control kicking in prematurely on rain-slick pavement. The 4WD system provides plenty of traction in such situations. I do feel the spin control is a bit over-eager in snow. In those situations, the spin control can cut in a bit too quickly, shutting down the throttle. You can turn lock the center diff (thus defeating the spin control) in the snow, but then the truck gets a bit tail happy. These days, I only lock the center diff when I'm offroad. The true answer to this issue is to get snow tires. Once you do that, you'll have all the traction you'll ever need in the snow.
  • I am confused again. If traction control and spin control are different, what does each one do?

    I was not asking about the ability to prevent vehicle understeer, oversteer, and turnover. Instead I was asking about the ability to send power to wheels that have grip to pavement or tractionable snow or tractionable ice.

    Once I can get going, I usually can drive cautionsly enough with a good set of tires to stay in reasonable control. If I cannot get going at all I'm in big trouble.

    I know the importance of good tires. I do appreciate very much what you folks are saying about this. I have had some really bad all season tires that I threw away practically new at great replacement cost, but I felt my life and the lives of my passengers, (and everyones property too) was worth it.

    I have had to use center differential lock and lo range on some of my older full-time 4wd suv's to get off of ice. That's why I'd like to know if 4 Lo automatically locks the center diff and if locking the center diff disables the limited slip system on the rear (whatever it's called), and if the limited slip effect works on the front diff / wheels too.

    I've used limited slip clutch pack rear diffs and they stink on ice and snow. Vehicle fishtails dangerously.

    I've used viscous limited slip on rears and centers operating in conjunction with standard open diffs and they worked great for me. Always got me going and no fishtailing.

    I've used computerized electromechanical center diff systems in the center and they worked well, though not as well as viscous limited slip on top of standard diff.

    I've never used torsen diffs at all, but they have a good rep.

    I've never had computerized brake control limited slip (whatever Toyota calls it). I came here to get info.

    I appreciate all the help you folks are giving me.

    Looking to buy a new 4Runner V8 Sport Edition.

    Have driven truck / suv's before. Know they ride hard. Just wondering what degree of punishment Sport Edition will doll out. :-)

    Thanks again.
  • 2toyotas2toyotas Posts: 104
    I think when Nedzel says spin control he means VSC Vehicle Stability Control,which corrects oversteer and understeer around turns primarily. When you lock the Center Differential VSC turns off. Traction Control never turns off, and it works on all 4 wheels independently all the time. When the center diff is unlocked the torsen splits power front to back,normally 40% front and 60% rear. It can send up to 71% to the rear, and 53% to the front. Traction control send power side to side on the front and rear axle by braking the slipping wheel. When you lock the center diff both axles get 50% and traction control still does its job.

    When in low range the torsen still works, or you can manually lock the center diff. Traction control does the same thing in low range.

    The Sport uses XREAS suspension which I have on my Limited as an option. It links the front right shock to the left rear, and the left front shock to the right rear. It works great, and in my opinion makes the 4Runner one of the smoothest body on frame SUVs on the road.

    As for traction on ice and snow, it will plow through anything, and start on ice with no problem. If you drive cautiously you will be fine stopping, but it will slip on hard stops. Snow tires change that, I put Blizzaks on my 4Runner, and the slipping stopped. It will stop on a dime on snow and ice. An All Terrain tire like Bridgestone AT Revo will do a pretty good job too.

    In my opinion you will not be dissapointed with this truck!!
  • Thank you very much. Now I understand clearly.

    Is there any kickback in the steering wheel when the brakes clamp down on a tractionless spinning tire on the front axle ???

    "No kickback" in steering was supposed to be one of the advantages of using either a viscous limited slip with standard differential on the front axle of 4wd's or a torsen type differential on the front axle of 4wd's. Clutch pack diffs tried on the front axles supposedly snapped the steering wheel hard when they locked for those who dared to try it.

    How does the Toyota traction control system behave as felt through the steering wheel when a front wheel gets locked down ???

    Thanks again.
  • wwestwwest Posts: 10,706
    The Toyota traction control system, as with most others, always brakes both front wheels even though only one may be slipping. And keep in mind that this isn't "full" braking ability by any means, moderate, on and off braking much like ABS "feel" and sound but with reverse duty cycle, more off that on.
  • 2toyotas2toyotas Posts: 104
    Wwest you are dead wrong. The Toyota system has a 4 Channel ABS system, it brakes all 4 wheels independently. If one front wheel is slipping it brakes just that wheel, and the open differential sends power to the other wheel. Where do you get your information?
  • wwestwwest Posts: 10,706
    Having 4 channel ABS capability doesn't mean the traction control firmware is (or should be) set up to bust knuckles or yank the stearing wheel from an unexpecting, inexperienced, driver's (John Q. Public) hands.

    Besides which doesn't the 4runner allocate engine torque 30/70 F/R in AWD (non-locked center diff'l) mode? That would make it unusual, rare, for a front wheel to break traction first.
  • I have V6 4WD but was not brave enough to try. Still wondering myself.
  • chiefjojochiefjojo Posts: 39
    I have a 2002 4R. When I lock the center diff in 4WD, VSC (yaw control) is off--no argument there. There is some confusion about whether the TRAC function stays on or not. Toyota has used versions of this system since (I think) 1999 or at least 2001 with the 4Runner. With the new FJ, Toyota has clearly spelled out that there are two versions of the same traction system, TRAC and ATRAC. I believe this is a newer version (3rd generation system?)of the same system Toyota has been using for a number of years now, including the 4R and Sequoia.

    TRAC (traction control) works in 2WD-Hi or 4WD-Hi with open center diff (essentially AWD or full-time 4WD-Hi mode where you can drive an any surface). ATRAC works in 4WD-Hi or 4WD-Low with center diff locked (off-road mode if you will). I believe there is some difference in how it works based on whether you are on or off-road. In my experience, TRAC (on road) will brake all four wheels if slippage occurs, whereas ATRAC (off-road) I believe will allow continuous wheelspin to at least one wheel (while braking the opposing wheel across the axle) on the front and rear axles to allow the truck to regain traction in off-road conditions. IE, if the right-front and left-rear wheels are off the ground, ATRAC will apply braking force to those wheels, but allow the left-front and right-rear to spin freely in the dirt/mud/sand/rocks to gain traction.

    Oh, and BTW, the 4R up to 2000 and the current FJ Cruiser has a rear locked diff option. The old 4R had no VSC/TRAC/ATRAC though, whereas the new FJ does have that too. But, only the 6 speed FJ has the full-time 4WD (Hi, Hi w/ center diff locked, and Low w/ center diff locked) with center diff (rear diff lock is standard), whereas the 5-speed auto version has only a part-time 4WD with no center diff (2WD-Hi, and 4WD-Hi and 4WD-Low for off-road conditinos with the rear diff lock being optional).

    This is my understanding of the system. Everyone got all that? :D
  • I think we need to get the guy who designed these systems to give us a lecture by posting. :-)

    Okay, um, I know that 4Runner has two different transfer case options. In the V6 the transfer case can be set to rear wheel drive (2WD). Toyota for some bizarre reason calls this a part-time system. This is very confusing for the reason that older 4wd systems in many SUV's and pickups had no center differential at all and thus could only be used on slippery surfaces to avoid axle bind-up and tire scrubbing. That no center differential system was called part-time 4wd because it could only be used part of the time (snow days and mud festivals). Toyota's part time definition simply means that you can use rear wheel drive if you choose to, not because you have to. Toyota's part time system does have a center differential.

    The V8 4Runner has a full time system which toyota means to say that you cannot operate in rear wheel drive or front wheel drive alone. Everyone else in the industry calls this (AWD) All Wheel Drive.

    Now chiefjojo are you saying that Trac is for the "part time" transfer case and ATrac is for that "full time" transfer case ???
  • wwestwwest Posts: 10,706
    Anytime the center diff'l or transfer case is locked the vehicle should NEVER be driven on a tractive surface. That's where, and only where, the term "part-time" comes from.

    It gets really confusing when vehicles like the 4runner are equipped with both full-time AWD and part-time 4WD/4X4 modes.

    AWD systems seem to come in three "flavors" currently, a fully open center differential with the brakes being used to prevent wheelspin/slip and thereby apportion engine torque, ue of a VC to "partially" lock the center diff'l with wheelspin/slip, and of course the Torsen center differential.

    4WD/4X4 systems, in general, always use a locked center differential and therefore constitute Part-Time systems since they cannot be used, should NEVER be engaged, on tractive surfaces.

    My own personal differentiation of 4WD versus 4X4 is that the 4X4 uses a transfer case, planetary gearset, so a low gear range can be provided.

    ABS functionality is ALWAYS disabled in Part-time, locked center differential, mode. We all know that during braking the weight "shifts" toward the front and therefore the front brakes take on the "brunt" of any braking effort.

    That means that during braking the front wheels almost always turn slower than the front. If the center differtial is locked then ABS activity at the rear would result, by default, in the same activity on the front.

    Therefore I would be VERY surprised if traction control isn't also disabled in 4WD/4X4 mode. With the center differential locked traction control braking at the front would also result in braking control of the rear driveline.

    Insofar as VSC is involved some aspects may be disabled (rear braking to aid in recovering from understearing comes immediately to mind). While front differential braking, or "unbraking" to prevent over-stearing might remain enabled.
  • 2toyotas2toyotas Posts: 104
    Sequoia, 4Runner, and Land Cruiser all use ATrac and Highlander, and Rav4 use Trac. The only difference is Low Range. ATrac changes from gradual fluid pressure control for stability-priority in High Range on all 5 that I mentioned, to sudden fluid pressure control for drivability-priority in Low Range. The second mode is for rugged offroad driving. The Highlander and Rav4 do not have a Low Range so they get plain Trac. When the center differential is locked in either High or Low engine output is not reduced as it is in the unlocked mode. Also when in Low range and in 1st gear there is gradual fluid pressure to the front wheels to keep control going down hill.

    On the FJ Cruiser Trac operates in 2WD or 4WD high, but shuts off in Low Range. In Low Range you have an option of both ATrac and a locking rear differential, both are engaged by a switch. When you lock the rear differential, ABS and ATrac are disabled. Two interesting things, when you lock the rear diff. ATrac does not work, so the front has only an open differential. Second you can now shut off ATrac, will we see this on 4Runner, Sequoia, and Land Cruiser? The rear diff and ATrac are an option on the FJ, but come together. So you either have both or nothing.
  • 2toyotas2toyotas Posts: 104
    ABS always functions with the center differential locked on all Toyota vehicles. Traction Control also works when the center differential locked. VSC is disabled when locked. The only time ABS and Trac turn off is if the rear differential is locked, and that is only on the FJ Cruiser and the Tacoma.
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