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Toyota 4WD systems explained



  • wwestwwest Posts: 10,706
    On the other hand should, when, the transaxle in my '01 RX300 finally fails, expected prior to 100k miles, now at 80K, I will be converting the RX to R/awd.

    The center differential front drive spider gears will be removed and the rear drive spider gears will get welded into place. Eliminating front mechanical drive and SOLIDIFYING the engine drive coupling to the rear. I will also be installing a new VC from the 99-00 RX series so that torque coupling will automatically be coupled to the front upon/with rear wheelspin/slip.

    So, my preference is quite clearly some sort of R/awd system such as is in my '94 Ford Aerostar. In the absence of R/awd availibility I would always choose RWD, tire chains on board, for travelling on wintertime adverse roadbeds.
  • beachfish2beachfish2 Posts: 177
    I've been surf fishing the Outer Banks since the early '70s and it's more about knowing how to drive on the beach than it is the vehicle. We started out using rear wheel drive trucks with large nearly bald tires. Tread only aids in digging you into the deep, soft sand when a wheel spins.

    I haven't taken my '10 HL Limited out yet, but there were a few older ones at Cape Hatteras 3 weeks ago and they were getting around. It's funny having 19" wheels now, after driving an '86 Subaru GL wagon with 13" wheels on the beach for 14 years. It's all about ground clearance and letting enough air out.

    Take a tire gauge, a shovel, a board and a snatch strap no matter what you drive.
  • 2toyotas2toyotas Posts: 104
    The new Sequoia, land Cruiser, FJ with a stick, and Limited 4runner, all use a torsen center diff that can be used on all surfaces. The Tundra, and tacoma still use a part time transfer case with no center diff. I have a 2006 tundra and it is really good in wet conditions in rear wheel drive. I know what you mean though. I keep saying if they put a full time transfer case in the tundra I would buy a new Crew Max. So I keep waiting and hoping. But yes the Torsen is still being used despite what "SOME PEOPLE" say.
  • Don't go through all those 2000+ post. Please forgive me if someone asked before.

    Could some explain what the 4WD/AWD systems are in recently Toyota models? Are they full-time 4WD, full-time AWD, or just part-time/auto AWD? I am specially looking for Sequoia, 4Runner, Highland, and Sienna. The first post of this thread is from 2001 and lots things have been changed. Thanks.
  • stateofmainestateofmaine Posts: 30
    edited December 2010
    this will help you get started:

    please note that it is dated 1/09, so not all the model information is entirely up to date.
  • shangydshangyd Posts: 25
    edited December 2010
    Nice Tutorial. Thanks.

    did a little search and found the updated version:

    4Runner: no multi-mode 4runner. limited would be full-time 4WD. other 4runner would be part-time 4WD.

    Sienna: on-demand AWD.

    all bad things for me.
  • thanks for posting the link to the updated version. sorry it wasn't happy news for you.
  • wwestwwest Posts: 10,706
    The thing to keep in mind, REMEMBER, is that there is NO such thing as a FULL-TIME 4WD or AWD system for, in the manner, for which you wish to make use of one.

    Yes, the Highlander, for instance, has a FULL-TIME 4WD system, right up until you reach the point of actually needing to make use of 4WD traction capability. At that point, wheelspin/slip, any one wheel or wheels, the HL reverts to it's true nature and becomes a ONE-WHEEL drive system.

    Absent TC, Traction Control, capability you would now be STUCK...!!

    But while TC might often be your savior in this situation in many instances it will operate to your detriment. Which is why most F/awd systems have a TC disable switch.

    So be very careful of any Base FWD vehicle, crosswise mounted engine, that makes claim to having FULL-TIME "4WD" or "AWD" capability/functionality. What they most likely mean is that the "AWD" system is ALWAYS enabled, but only activates REACTIVELY once/after wheelspin/slip is detected.

    The 2011 Porsche Cayenne, and likely its VW & Audi brotheren, are about the only R/awd systems available that I know of. These can be both pre-emptive and reactive, with SAFETY.

    Pre-emptive in that like the new Sienna, Vensa, and RX350, they can and will automatically engage the front drive torque under the driving conditions which are most likely to result in loss of drive traction, low speed acceleration. But UNLIKE the Sienna, Vensa, and RX350 they have no need to REDUCE the drive drive torque during tight turns or acclerating turns since it is the rear wheels that provide the primary drive forces.
  • Good post, WWest. Always enjoyed reading your insights on this awd stuff.

    Got a question for you: we recently got an accord crosstour with "on demand 4wd". The system works by using a hydraulic circuit to engage the rear wheels when there is a speed differential between front and rear wheels during slip.

    The issue centers on the use of snow tires on dedicated rims...something we have always done for our cars.

    In this case, however, we have a tire pressure monitoring system, and making it work with the snows on their own rims involves not only outfitting the rims with sensors, but also "re-registering" the different sets of sensors with the car's computer....something that costs about $70 at the dealer twice a year. Not very attractive.

    Alternatively, Tirerack says about half of their customers just forget about the sensors with the winter tires and live with the TPMS warning light during the season.

    Only problem is that in this car when the TPMS warning light is on you cannot disengage traction control. Am I correct that disengaging traction control might be exactly what I would need to do to get myself unstuck in the snow?

  • mdhuttonmdhutton Posts: 195
    OK wwest - I haven't always agreed with your posts, but I've come to respect them. If you owned a 2008 HL Limited 4WD (gas), how would you operate it in Chicago's snow to get the best performance from it? Based on your responses, you would engage the SNOW button and turn TC off. Yes/no?
  • wwestwwest Posts: 10,706
    " cannot disengage traction control.."

    I strongly suspect that's because TC is automatically disabled with a TPMS warning light on.

    Early TPMS's used the ABS "tone wheel" to judge that a tire was under inflated. TC also relies on those same ABS tone wheels to detect the onset of wheelspin/slip. The TPMS fault indicates that use of the tone wheel for TC functionality might be "suspect" so I doubt it would be, remain, active.

    Check your owners manual.

    But ABS might also be disabled for the same reason. If so it would not be a good idea to drive in adverse conditions with a TPMS fault indication.
  • wwestwwest Posts: 10,706
    For all practical purposes I do own a 2008 HL 4WD....

    Mine just happens to be a 2001 RX300 "F/awd". With the advent of the use of TC starting in '01 the TC remains in the "mix" but with the viscous fluid reformulated to forever remain "flaccid".

    So I have the very same drive train implementation as you.

    The first thing I did was add wheel spacers all around and 17x8 wheels with the appropriate +1 summer use only tires, Brdigestone Turanzas, to be exact. The spacers not only allowed for wider tires, more roadbed contact area and wider "stance", but also room between the suspension and tire in the rear such that I could make use of tire chains in the rear initially and only add the front chains at times of real need.

    I would NOT advise disabling TC as a rule of thumb, not, NEVER, on a FWD or F/awd vehicle. TC is a totally REACTIVE feature, only activating AFTER the fact, after wheelspin/slip has already become an issue to be dealt with, URGENTLY dealt with.

    Engage the snow button, YES, indeed.

    Tires..Mixed bag.

    The following is my personal opinion ONLY.

    I am of the firm belief that the clear majority of the time my summer tires provide superior traction, above ANY wintertime specialty tire. The "clear" majority being dry, wet, icy, or packed snow roadbeds. Specialty tires have less surface CSA, less traction on a "solid" surface roadbed. Winter tires are only advantagous on "soft" roadbed surfaces wherein that tread blocks have something to "dig" into.

    But my advice to you is to buy the best all-season tires you can find and trade up to a R/awd or even a RWD vehicle ASAP. I had expected the new 2011 HL to have adopted the Venza, Sienna, and RX350's new F/awd system but apparently not. This new F/awd system could be easily modified to a PART-TIME 4WD system using a manual switch to over-ride, temproarily close the circuit to the rear clutch. Obviously that switch should ONLY be used in KNOWN adverse conditions, SLIPPERY roadbeds.
  • wwestwwest Posts: 10,706
    What is the advantage, cost, etc, of purchasing a set of dedicated wintertime wheels and TPMS sensors vs just simply having a tire shop swap tires twice a year..?
  • Reasonable question. The price for four BlizzaK Tires mounted on new steel wheels is about $650, and the TPMS monitors are $116 for a set of four (Honda sensors are inexpensive compared to many other brands for some reason). So it is about $775 for the whole shooting match including sensors.

    The Blizzak's alone are $430. Mounting and balancing around here is about $20 per tire.

    So here are my options and the prices:

    Dedicated tires/rims and no sensors: $650 (one time charge-I change these myself) Disadvantage- either cannot turn traction control off, or --as you suggested--traction control is always off if system sees no TPMS sensors. I think that ABS still works in this vehicle under these conditions.

    Dedicated tires/rims with sensors: $775 plus $80 twice a year for the Honda guys to reinitialize car's computer each time for the alternate set of sensors (winter vs summer tires).

    Tire shop swaps tires twice a year: $430 plus $80 twice a year (this time the same $80 is spent on the tire changeover instead of the sensor re-programming)
    I guess I wasn't considering this because it is so convenient for me to just switch out my own tires in the driveway with a floor jack vs taking it to a shop and waiting. Also, my nice rims don't get mucked up in the winter.

    Thanks for the comment about the possibility that traction control is already disabled with TPMS light on...I never thought of that and will research this more and comment back. Just read the post today.

    Many thanks.
  • misaakmisaak Posts: 3
    Where do you buy the tires for $430 for Blizzaks?
  • danielldaniell Posts: 128
    edited January 2011
    1) You can get cheaper winter beater wheels.
    2) You can get -1 or -2 size wheels. With those, you will need tires with taller sidewall which give better traction in snow and slush. Those are cheaper too, and the difference is significant for most brands.
    3) I am not sure how much it costs to swap tires, say $50-$80. That's $100-$160 per year. Over a few years it adds up. If you keep your vehicle for a long time, it's proably cheaper to get the second set of wheels. Swapping wheels is something I can do myself in my garage, it takes me about 40-50 min., probably less than driving to a tire place (with 4 dirty tires in the trunk), and have them balance and swap the tires.
    4) All that repeated swapping can't be good for tires.
  • "F/awd system could be easily modified"

    My 09 HL one wheel drive is nearly useless in the snow and I am wondering how one would go about modifying it as you described using a switch to over-ride the the clutch.

    In your opinion would this help substantially or is it just wishful thinking?

    I am pretty handy with a tool and would seriously entertain this idea, realizing of course (hoping really) that it would be like locking in a tranfer case.
  • wwestwwest Posts: 10,706
    Sorry, but I was referring to the NEW F/awd system now used in the Sienna, Venza, and RX350. Those have an electromagnetic clutch just forward of the rear diff'l that is used to dynamically apportion engine torque to the rear drive.

    In those a simple switch might be used to fully engage the rear clutch provided that there is absolute certainty of a non-tractive, slippery surface.

    Basically a "part-time" 4WD system.
  • donovancookdonovancook Posts: 1
    edited June 2011
    2003 Toyota Sequoia 4X4

    Is there a way to override the TRACS and VSC system? I was heading up a muddy slope and it felt like the rev limiter kicked in and I couldn’t power up the rest of the way – it felt like it was trying to get traction and slowing the revs of the motor to do so.

    Am I able to flash my ECU, pull a fuse, or snip a wire? Did I just buy a soccer mom taxi?

    Thank you in advance for any insight or explanation anyone can extend.
  • wwestwwest Posts: 10,706
    In a true 4X4 if you lock the center "diff'l" that automatically disables TC and VSC. Sounds like in the conditions you had you needed to be in "locked" 4X4 mode.
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