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Toyota 4WD systems explained



  • ustazzafustazzaf Posts: 311
    Thought this was interesting. During our last snow storm, which was 18 inches my brother and I went to an unplowed lot which had a nice hill. He has a V6 4Runner and I had my Double Cab Tundra. Both had Blizzak snow tires on them. My Tundra does not have VSC or Trac, just a plain Limited Slip rear differential. We both tried the hill in 2WD, and both got stuck near the bottom. He switched to 4WD unlocked and continued with no problem at all. I switched to 4WD, and it still would not move. I had to switch to 4LOW, and it then walked up with no problem. My point is this, after getting stuck pretty good in 2WD, it was much easier to get unstuck with A-Trac. My Tundra has an open differential in the front, so it did not help much. I have a Sequoia, a 4Runner, and a Tundra, and when it snows the Sequoia and 4Runner are more sure footed than the Tundra. They plow through everything like a walk in the park.

    I find that very interesting. For one thing, I never had any trouble in snow, mud or anything else with my Tundra in 4High. Also, switching to 4 low does nothing but increase power. It does nothing at all for traction. Infact, low range can be a disadvantage in snow and ice because of the added torque.
  • 2toyotas2toyotas Posts: 104
    My Tundra would have plowed through the lot and up the hill with no problem in 4High, but I wanted to see how far I could get in 2WD. It did OK until I started up the hill, the tires began to spin, and it would not move. I needed to go to 4Low to continue. You better do your homework on this one because 4Low adds torque, but with very little wheel spin. It absolutely gives better traction, and is a big advantage to move on snow and ice. It puts a lot of torque to the wheels to move the vehicle, while you creep along. Spinning the rear wheels in 2WD buried them and switching to 4High only added one front wheel, because of the open front diff. The vehicle still would not move. I could have spun the wheels to try to move it, but why heat up the limited slip diff, when 4Low moved me up the hill with no problem.
  • wwestwwest Posts: 10,706
    Sorry, I have to step in and disagree on this one. 4-low only allowed you to use your leadfoot a little more effectively. In 4-high you were being too agressive on the throttle. You didn't get more traction in 4-low, you just reduced the "gain" of the accelerator pedal, not as much potential for wheelspin.

    4-low vs 4-high increases the level of torque available at the drive wheels, not the level of traction.

    You could have very likely accomplished the same thing in second or even third gear, and quite possibly even in 2WD. Next time try feathering the throttle just a bit to the point wherein the tires do not quite break traction with the surface.
  • 2toyotas2toyotas Posts: 104
    First of all I was not heavy on the throttle at all. Second , instead of trying all that, I put it in 4Low and it moved with no problem. Call it what you want! 4Low multiplies the torque applied to the wheels, in turn giving you the ability to move the vehicle! Sounds like more traction to me. I was trying to see how far it would go in 2WD before struggling. It dove through the lot, but struggled to go up the hill. I was not going to heat up the limited slip diff, when I could simply put it in 4Low and continue. How many RWD vehicles drive through 18 inches of unplowed snow, let alone a steep hill? My point was the 4Runner with A-Trac continued up simply by engaging 4High unlocked. He did not have to feather the throttle or try putting it in second or third gear. He pressed the gas, and continued on. The Tundra did not. In my opinion, I would rather have A-Trac then a Limited Slip rear Diff. in the snow.
  • harboharbo Posts: 136
    What wire did you pull to disconnect the Traction Control?
  • harboharbo Posts: 136
    How do I permanently disengage the Traction control so I the engine power is there to use in loose sand, mud etc.? The stepping on and off the emergency brake etc etc etc everytime is a pain.

    slvrfx :shades:
  • nobody3nobody3 Posts: 27
    Thanks for the interesting information.
    I agree, one would get high torque with 4LOW. But, I think it is the reduction in wheel rotation rate associated with 4LOW that helped to get better traction. Like taking baby steps when the surface is slippery.
    Concur in other deductions.
  • wwestwwest Posts: 10,706
    If you unplug the MAF/IAT module connection, just downstream of the engine air filter, while the engine is running the engine will die. Plug the connection back in and restart the engine.

    Except for an engine check light being on everything will now operate as normal except for VSC/Trac which remain disabled until the check engine light clears after about 4 drive cycles.

    Instruction given to me by the service manager at Lexus of Bellevue WA.
  • wwestwwest Posts: 10,706
    Yes, less wheel "speed" for a given level of accelerator pedal travel, making it a lot easier to "feather" the throttle.
  • harboharbo Posts: 136
    Thanks WWest, I wonder if the same may work on my 02 Lexus GS 300??
  • 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.
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