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Toyota 4WD systems explained



  • my001my001 Posts: 17
    Get this from 2007 HL Buyer's guide:

    Four-cylinder and V6 Highlander models are available with a four-wheel drive system that distributes engine power 50:50 front-to-rear, with four-wheel traction control (TRAC) controlling potential slippage at any wheel.
  • 2toyotas2toyotas Posts: 104
    First the rear is not overdriven by the front. It would be if the transfer unit ratio was 1:1, but it is not. The transfer unit ratio is .34:1, and that makes up for the different ratios front and rear. Power is 50/50 until a wheel or wheels slip and then trac steps in.

    I don't know who told you trac brakes both front wheels at the same time, but that is the craziest thing I have ever heard. It will brake each front individually when they begin to slip. Trac uses gradual brake fluid force to keep stability.

    My Tundra Has the same warning about the Auto LSD option. And that only works in rear wheel drive.
  • wwestwwest Posts: 10,706
    If TC will brake each front wheel individually why is an "auto" LSD function/mode required?
  • 2toyotas2toyotas Posts: 104
    It uses less engine dethrottling. It will act like a mechanical LSD. When I use it on my Tundra it will allow more wheel spin. The reason toyota uses it is to help get a vehicle unstuck by allowing a lot more wheel spin, unlike Trac which when in 2WD can really bog forward progress down.
  • wwestwwest Posts: 10,706
    Yes, if TC, in "auto" LSD, is allowed to brake only a single slipping wheel then engine dethrottling serves no purpose. It's only in normal traction mode that both front wheels are braked with only one slipping therefore the engine MUST be dethrottled.
  • 2toyotas2toyotas Posts: 104
    Agree to disagree!!
  • Can somebody please explain to me why the RAV4's system is called a "4WD" when it is not selectable and is (almost) completely automatic in its functioning? If I had to guess, I would apeculate that the locking function being user selectable makes Toyota's legal department loath to putting an AWD label on the system.

    Having read the posts that I have, including one driver who apparently kept the 4WD lock feature on during all in-town driving (thus explaining his reported 13 MPG) I really wonder why they even included the locking feature at all.
  • chiefjojochiefjojo Posts: 39
    "in normal driving, even on snowy roads, leave the center diff unlocked. If you are going offroad, then lock the center diff."

    I think this should be repeated for those who may have the toyota trac system... there's no need that I can think of to ever lock the center diff while on road.
  • zangzang Posts: 2
    My wife just purchased a 2005 RAV4 after 12 years of owning a Camry. We've noticed poor gas mileage and wondered if the rear wheels can be disabled of the 'always-on' 4WD?
    We don't need 4WD at all and have never had it. Mechanical solution?
  • zangzang Posts: 2
    Ummmm.............I need a little more info to accompany your response......
  • nedzelnedzel Posts: 787
    Even if you traded it on a 2WD model, you wouldn't increase your mileage much -- 1 or 2 mpg tops.

    If you want better mileage, trade it on a sedan, hatchback, or wagon. The large frontal area of an SUV/CUV increases wind resistance, greatly reducing mileage.
  • harboharbo Posts: 136
    This dethrottling is really a dangerous situation. Wet or dry sand, mud, high water situations cause the vehicle to loose forward motion and now you are either completely stuck or in the case of high water may be washed off the road. Dangerous and stupid. What is the best way to shut it off (or) have an off / on switch.

    THX ....... love the Sequoia accept for this ridiculous intrusion in my driving ability and safety.
  • wwestwwest Posts: 10,706
    Advice given to me several years ago by the service manager at Lexus of Bellevue WA.

    On my 2001 RX300 if I unplug the MAF/IAT sensor module while the engine is idling CEL/VSC Trac faults will result, the engine will die, but can be restarted after the sensor is reconnected.

    Thereafter for the next few drive cycles the VSC/Trac system will be disabled.

    There are remote wireless relay systems available in the marketplace that I'm sure could be rigged up to do this from the driver's seat.

    I use one, wireless relay, to open the door of the GPS/Nav DVD player so as to get rid of the "I agree" and moving mao display at times, MOST of the time, that I have no use for GPS.
  • 2001 Toyota Tacoma 4wd indicator light stays on. The 4wd drive engages and disengages just fine, but the 4wd indicator light stays on all the time. The dealer claims that it is the actuator switch. This doesn't seem right, because the 4wd works just fine. Any thoughts?
  • wwestwwest Posts: 10,706
    Are you sure, CERTAIN sure, the 4WD disenagages?

    How do you know?

    If not you will soon be looking at some pretty severe charges to repair the DAMAGED parts of the driveline.

    That being said the indication could be the result of a misaligned sensor switch mounted on/at the spline clutch actuator. The spline, "dog" clutch is disengaging but the switch remains "tripped". Same as like your backup lights always remaining on.

    I'm surprised that your dealer treated this issue so lightly, unless the clutch really is disengaging this can result in some damn serious driveline damage.
  • Now I'm worried! I'm not absolutely CERTAIN that it disengages or not. The way I was telling if it was engaged or not was the turning radius changed while it was in 4 hi. What is the way to be certain it is disengaging? I agree, the dealer was very light on this subject.
  • wwestwwest Posts: 10,706
    If it's still engaged and you make a really TIGHT turn on dry pavement you should feel the resulting driveline "windup" in the stearing wheel "kick-back".

    I don't know of any reason why the turning radius would change in 4-hi. Perhaps(???) you have been feeling the stearing wheel "kick-back" while turning on dry pavement and thinking that kick-back was a limit to how hard you could turn the stearing wheel...

    I don't know if your Tundra uses a spline clutch to engage/disenage the 4WD mode, lock the center diff'l, but if so those clutches are notorious for becoming reluctant to disenage as they are typically not "driven" into the disenaged position. The least amount of friction or binding, or even "binding" due to driveline torque, will tend to keep them from disenaging.
  • I took my Tacoma for a little test ride and engaged the 4wd into 4 hi and could feel and hear it engage and the steering did change a bit. Just enough to feel a bit of drag. It feels quite a bit different than when it in 2 hi.
    So I'm sure it is going in and out of 4wd just fine.
    Can that sensor switch that you mentioned earlier be replaced easily?
    2001 Toyota Tacoma 3.4L Manual transmission

    Thanks for all your help.
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