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Toyota 4WD systems explained



  • 2toyotas, you write about fluid pressure, but the center differential in the 4Runner is a Torsen type which is all mechanical with worm gears and worm wheels. There are no viscous limited slip units on any of the 4Runner differentials, nor are there any clutch-pak limited slip differentials on the 4Runner.

    So, are you writing about the brake fluid being pumped by the abs pump as controlled by the ATrac system ???

    Toyota should have just used Torsen diffs on the front and rear to minimize confusion on this forum :-)
  • 2toyotas2toyotas Posts: 104
    Yes brake fluid being pumped by the ABS.

    I had a Hummer H2 that I borrowed from a friend for a week, and it has Torsen diffs on the front and rear, and it was horrible on ice. I was driving it one night and it was slipping all over the place. When I got home I had a very hard time getting it up my steep driveway. When I finally did I was curious so I backed my 4Runner down and it went up with no problem at all. The traction control kicked in, did its thing and I didn't break stride. A torsen diff is good in the center because it keeps power going to both axles all the time without it being locked, but I prefer traction control controlling side to side traction especially for snow and ice. The Sequoia had all open diffs until 2005. I had an 03 and an 05, and the 05 with the Torsen center diff made a big difference. Also the Highlander had a Viscous center diff from 01 till 04. In 04 they took the Viscous out of the center and used an open diff with Trac. For 07 they are going back to a Viscous center diff, so it must be better to have a limited slip unit in the center, this way both axles are always getting power.
  • Thanks for the reply 2toyotas. Seems like Toyota does its homework well :-). During the time when I had a vehicle with a viscous slip limiter working in conjunction with the center diff and a viscous slip limiter working in conjunction with the rear, I drove in snow and ice and never got stuck or fish tailed. When I first got it I tried taking off hard on snow and ice in a deserted area (with nothing to hit :-) ) to see what would happen. Absolutely nothing other than the vehicle just went where I wanted it to. Safe to the point it seemed like I was on dry pavement.

    From what I have read, the "Trick" with the Hummer and other vehicles that have Torsen's on front and/or rear that are not "pre-loaded" (a designed in drag to compensate for one of the design anomolies during a zero traction event) is that when you are trying to get up an icy driveway or out of an icy parking spot, you have to two foot the brake and gas simultaneously. The drag of a small amount of braking action while accelerating causes the Torsens to avoid that zero traction anomoly and do their thing. I have never had the pleasure to try this personally with a Torsen diff, but I need to do it on one of my clutch pack diff vehicles and it does seem to work as described.

    Next time your friend gives you a turn at the wheel, give it a try and let us know if the theory from the Hummer instruction manual actually works in practice on the vehicle.

    Incidently in this month's Four Wheeler mag they put Torsens into a project vehicle for mud and dirt and their review was that it was better than a "locker" for those purposes.

    Thanks for all the helpful info.
  • wwestwwest Posts: 10,706
    For the aforementioned reasons NONE of the braking related functions, ABS, VSC, Atrac, Traction, etc, will be enabled with the center differential locked.

    I have now read almost all, if not actually all, owners manuals of related vehicles (4runner, Sequoia, GX470, etc,)and in no place did it relate that these functions would be active with the center diff'l locked.

    Being well aware that doesn't cover the issue well I did find one statement saying that if the traction control's engine dethrottling mode interfered with vehicle manuverablity then the driver could lock the center diff'l to avoid engine dethrottling.
  • 2toyotas2toyotas Posts: 104
    Wwest I don't want to go back and forth with you but I own an 05 4Runner, an 05 Sequoia, and an 05 Tundra and ABS works on all three with the center diff locked. The Tundra does not have Trac and VSC, it only has ABS. It also is only part time 4WD and ABS still worked in 4WD. On the other two VSC does not work, but ATrac and ABS definitely work. Toyota would never leave their SUVs with open diffs when the center is locked, that would be pretty dumb. When the front or rear diffs are locked on an axle then ABS can not operate, but Toyota doesn't offer that.
  • neensawneensaw Posts: 4
    My 1997 Rav4 was accidentally put in C. Diff Lock, while I wasn't driving, (therefore not beeping) Having NO idea what the differential lock actually was, I of course kept driving. (This being my first car, and me being a teenager with no idea what I'm doing.) Now, after trying to take the Differential lock off, it won't stop beeping. Is it unsafe to continue driving while my car beeps? (The beeping is supposed to indicate that the Differential lock is still unlocking, but usually only takes 1 minute at most)What have I done!!!! Please give me some insight! :sick:
  • chiefjojochiefjojo Posts: 39
    I have 4Runner and when I unlock the center diff, I make sure I am in neutral or park first. Then as it blinks, either wait a few seconds for it to unlock or a trick is (while stationary) to switch between neutral and drive until it kicks in and stops blinking. If the center diff lock is still on, you should have noticed a lot of binding in the drivetrain (vibrations and difficulty steering) when driving on pavement, which can cause damage to the vehicle. Do not drive it if at all possible until you can unlock the center diff. I would say if this trick doesn't work, call a mechanic.
  • fkozilfkozil Posts: 65
    I recently acquired a '98 tacoma 4x4. The 4x4 system is not working. I jacked up the rear about 2-3" with a floor jack and engaged the 4x4. No 4x4 light came on and the truck would not drive off of the jack. The only wheel turning was the right rear. I tried the rear differential lock as well but had no luck. The locking diff. light flashes on the dashboard. Then I put the truck into 4 low. The rear diff. lock was then working as both rear wheels were turning and the light for the locking rear diff. stayed on however the truck still did not drive off of the floor jack. The front hubs are automatic and self-engaging. Any suggestions/comments are welcome.
  • I am not knowledgeable in the '98 tacoma 4x4 in particular but I can tell you that it is my understanding that automatic and self-engaging front hubs need to be turning in order to lock in. I realize this sounds stupid because if you are stuck on ice or snow and the front wheels are stationary because the rear has no traction and is spinning wildly you're just stuck looking for someone to push or tow you out. :-(

    On many, but not all vehicles, 4 Lo locks the center diff. If yours has a separate center diff lock, you need to turn it on to complete your test.

    HOWEVER, I WOULD NOT RECOMMEND TRYING TO DRIVE OFF A JACK. YOU'RE RISKING INJURY AND/OR VEHICLE DAMAGE. If your transfer case is not working right, you need someone with a lift and the factory diagnostic steps to safely figure this out.

    Good luck and stay safe.
  • Hi wwest,

    I got a response from Toyota and they said that the Center Differential Lock and the ATRAC system can "both be engaged at the same time."

    I asked them specifically about the 2006 / 2007 V8 Sport 4Runner, so that vehicle is the one they referenced their answer to.

    If you wish to ask them about your vehicle go to Toyota's website. It takes a long time for them to respond, so don't expect an answer for a while.

    Hope this is helpful to you.
  • I have a 3rd generation 4X4. Auto Trans. The smaller of the 2 shift levers has a button on the side which allows me to go into 4 wheel drive at just about any speed up to 60mph. When I am in 2 wheel drive and press this button in, the light flashes on the instrument cluster, until 4 wheel drive "kicks in" at which time there is a muffled clunk noise, and the four green lights come on indicating "You are now in 4 wheel drive". Here's the question. Sometimes it takes 5-10 seconds for this little process to occur, and other times it doesn't seem to want to work at all. Whats going on here? Is there a grease fitting that lubricates this process? Why will it not go into 4X4 or at least takes
    its sweet time. PS. I try to "exercise" this procedure every couple of weeks or so. Should I be doing this more regularly? Thanks for any help. As an aside.....I Love this machine, it is so solid, reliable, good looking, and tough. I will never, ever, ever buy another north american made domestic vehicle, GM, Ford, Chrysler....they are flashy, but underneath and inside, they are all crap. Thanks.
  • Toyodave, you must have a 99 limited model, which has the same 4WD system as my 02 SR5 model (minus ATRAC and VSC). In my experience the process you speak of is normal. When I shift into AWD (ie, 4WD w/ center diff unlocked) the light on the dash usually blinks for a few seconds and then there is a "muffled clunk" as it engages, as you said.

    If you are stationary, and want to shift in AWD, you can (1) press the 4WD button and shift the tranny into neutral and back to drive--this often helps engage and disengage the system quicker. If you are moving, you can either carefully follow step 1 or you can (2) blip the throttle on and off until it engages while driving in a straight line (I believe the manual recommends driving straight). The throttle blip technique has worked for me, but it can take 5-10 sec to engage.

    Just last night, I used step 1 (shifting in to neutral while parked), and it worked like a charm--took about 2-3 sec. I usually try to do that if I know I am going to be driving in the rain or snow, and leave the moving engagement of the system for the more rare occassions when weather conditions change while I am driving.

    Again, this is my own experience over the last 4 years of ownership. I hope it helps.
  • Thanks for your reply. I will try this technique next time I drive my 99 4Runner. I discovered another thing last week that helps it get into 4 wheel drive, and that is if you turn the wheel like your going to turn a corner, either left or right, (while the yellow blip is flashing on the intsrument panel), it also helps the 4 wheel drive to "kick in". I wonder if some gear or spline has to align "just so" before it will engage. If you didn't use your 4 Wheel Drive for a year I wonder if it would ever work again or what? Happy Driving
  • curlewcurlew Posts: 5
    I couldn't find this particular system explained - everthing seems to revolve about the TRAC system...

    I have a 2000 4Runner Limited with the button on the 4WD lever that allows you to engage what I _think_ is an AWD mode. I _think_ this has the 3 open differentials (please correct me if I'm wrong - the manual is completely useless here), but this vehicle doesn't have the TRAC feature installed on LCs of that year and 4Runners starting in 2001. 2WD mode, with an open rear differential (I don't have the locker anyway), in a low traction situation power goes to the wheel that's spinning, and you go nowhere. Now...putting it into this AWD mode, I extend this metaphor so that if either rear wheel slips, all of the power is transferred to the rear - and to the wheel that's slipping by the rear differential - and...well, you still go nowhere.

    If that's true, then it seems like the reverse would be true - if a front wheel were slipping, all the power would go there.

    And that's simply ridiculous - this system would seem to transfer all the power to the wheel that has no traction! Obviously, I'm missing something important here.

    Assuming someone can explain what my AWD system does (I think I've got a handle on the part-time 4WD part), I then have a followon question ...if one wheel is slipping (in snow, for example), what would be the effect of lightly applying the brake _and_ the accelerator? A light brake would stop that spinning wheel, right? Effectively a manual TRAC system?
  • I think what you're missing is this. With 4WD engaged, the rear wheels are not linked together so they will spin. However, I beleive during this time the fronts are locked together, that is to say, left or right front can't just spin away without the other on the same axle, turning also. Where it starts to get really good is if you have rear "diff lock". Your press that button (usually on the dash) and it locks the two rear wheels together, and now you have drive to both front and back wheels, and the wheels on the same axle are locked together, and therefore, no wheel spin, and it will be mighty hard to get stuck. Does this answer it?
  • curlewcurlew Posts: 5
    Well, it answers it if that were true. But you're saying that the front is "locked" in AWD? That just can't be true either - locking the front would make it impossible to turn since the outer wheel would travel farther (same issue as locking the center differential on pavement and then turning). Unless the front were a LSD rather than an open differential, or there were some other spin sensing mechanism like the brake thing. And we're talking normal everyday driving here, not loose conditions - so there should be (and as far as I can tell there is) no detectable difference in "normal" conditions.
  • You may be right about the front wheels not being "locked", and perhaps this is to enable you to steer......but, I know for a fact the rear wheels are "locked" because the manual says max 5mph, and not on dry pavement, and of course you can feel it. If as you say the front wheels cannot be locked together can you prevent the fronts from spinning on ice mud or snow? I still contend they are locked together, perhaps with an LSD. My original query to this discussion board was "why does it sometimes take so long for the 4WD to kick in when selected via the electronic push button on the 4WD stick?" Do you know the answer to that one? Thanks.
  • wwestwwest Posts: 10,706
    "..why does....."

    Because a "dog-clutch", spline type, coupling is used to lock the center diff'l. The splines must first line up perfectly in order for the shaft to slide into the lock position.

    SOP, nature of the beast.

    A slow creep will generally rsult in a quicker lock-up, and I sometimes had to put my Jeep in reverse.
  • Oh Ok. You know more than you let on. That's the first decent explanation I have had of that question....Thanks !!!!
  • harboharbo Posts: 136
    So what is the easiest way to "switch off" the TCS to avoid having engine power cut back when in soft sand, mud etc, that effectively guarantees you will sink? 35 / 40 MPH in shot sand conditions allows you to stay on top and keep moving nicely with a bit of slippage, but not much. When the engine power cuts off the vehicle sinks and now you have a real mess. "Computer intelligence" is an oximoron when you know how to drive.

    THX for your advice.
  • curlewcurlew Posts: 5
    The manual cautions against the dry pavement only when the center differential is engaged (4HI and 4LOW), not when the AWD mode is engaged.

    I see you got a reasonable answer to your delay question, but I hope someone can pipe up with a reasonable explanation of ho this AWD mode operates in pre-1991 4Runners. And whether my question about lightly riding the brake would be somewhat analogous to what the TRAC system does.
  • wwestwwest Posts: 10,706
    TCS disable.

    Simply unplug the ABS pumpmotor, or remove the fuse.
  • Egads - no response? Nobody knows how this AWD system works? I see I said "pre-1991 4Runner" in the previous message, but that actually should have been "pre-2001". Clearly that makes a difference...
  • harboharbo Posts: 136
    Anything else that gets cut off?
  • wwestwwest Posts: 10,706
    Yes, ALL the functions that require that the ABS pumpmotor be operational....
  • So what is the easiest way to "switch off" the TCS to avoid having engine power cut back when in soft sand, mud etc, that effectively guarantees you will sink?

    Lock the center diff and the system will still allow some wheelspin (by wheels that have traction) in sand and mud... no need to pull any fuses. I have an '02 model with ATRAC and it gets through sand and mud just fine. A lot of FJ owners actually PREFER ATRAC to using their rear locker. :surprise:
  • harboharbo Posts: 136
    My 02 2WD Sequoia has the nuisance power cut back as soon as wheel spin is detected, causing the vehicle to sink in soft sand, mud, snow etc., just when you need to maintain momentum. What is the easiest way to "switch off" this idiot computer control?
  • wwestwwest Posts: 10,706
    Unplug the connector to the MAF/IAT module while the engine is running, plug it back in, restart the engine and now you will have a CEL and VSC/Trac failure indication that will extinguish after a few drive cycles. In the meantime VSC/Trac will remain disabled.
  • 2000 4Runner, 4WD but no buttons, just H2, H4, L4 on transfer case. This afternoon got stuck in deep snow, shifted to H4 ... right front wheel spun and rear wheels did nothing nor did the left front. I don't know what's going on here but it seems pretty useless to send all the power to one spinning wheel, leaving the other three with no power. For reference, the only "button" on my shifter is the overdrive switch on the main (auto) transmission shift lever. What am I missing?
  • dreasdaddreasdad Posts: 276
    Did you shfit down to L4? Thats what you would need in that type of road. Right front tire was proably higher than all the others so had less wieght on them.

    Can't rember if the 200 had a center diff loack or rear diff lock but button woul dbe on the dash not on the gear shift.
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