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Toyota 4WD systems explained

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  • Ok, now it is obvious to me why electronic stability control cannot work if you lock differentials. So I am now convinced Active-Trac is the best system for driving at highway speeds in snow. It also seems there is almost no situation where locking the center diff would improve anything so perhaps it is one thing to try if you are stuck, but no need to ever go into that mode in anticipation of being stuck.

    My only remaining question is if it would be better for Toyota to use LSDs rather than open diffs front and rear.
  • wwestwwest Posts: 10,706
    I believe it is only ABS and TC that cannot be operational, fully functional, with the center diff'l locked. Except for A-LSD (brake implemented LSD functionality) the front and rear diff'ls are still mechanically "open" R/L-L/R differential braking can still be used for stability control.
  • buskybusky Posts: 2
    my 07 tachoma top hwy mpg is 15.5 dealer says no check engine light no problems, they suggested putting different tires on the truck,(my wallet), the tailgate was replaced at 1,500 miles because it would not hold the weight of my harley, the plastic compartments in the bed keep falling out, right rear speaker rattles, hood flops from windgusts. FOR SALE only12,000 miles. i bought this truck on the reputation of past toyota trucks, so much for that.
  • I thought this was the "Toyota 4WD systems" forum, but I'll address your post. First, try posting in the Tacoma forum for more responses related to your Tacoma. Second, it's wintertime, when MPG usually takes a dive due to different gasoline formulations and of course cooler weather. Third, Michelin and Dunlop tires give better MPG than Bridgestone's. Fourth, the speaker and hood adjustments can be taken care of under warranty. Fifth, the tailgate shouldn't be expected to support the weight of an 800lb or heavier Harley. Sixth, no vehicle is perfect. My 4Runner had the radio replaced at 1100 miles and the VSC warranted at 11,000 miles. I've had no problems since except for lousy dealer maintenance..

    You won't have any trouble selling your vehicle should it not meet your expectations. Your post makes it appear though you needed a vehicle with a longer bed to begin with so your Harley wasn't riding on the tailgate. My neighbor has the same vehicle as yours in the DC configuration and has had -0- issues. Another neighbor got a DC 4X4 shortly thereafter, and has no complaints either. Both are 2007 models.
  • tidestertidester Posts: 10,109
    You'll want to ask in one of the Toyota Tacoma discussions.

    tidester, host
    SUVs and Smart Shopper
  • Cliffy1: As someone trying to buy either a 2005 or 2006 Toyota HLander, your postings are invaluable. Far more understandable information than any dealer I have talked to. I travel a lot of semi-rural back roads in a variety of weather conditions (snow, sleet, rain) and sometimes in Northern Maine I have to drive logging roads for several miles. Am I right in assuming that I should hold out for a 4WD HLander and not touch anything else (e.g. "all wheel drive") or any system that doesn't specifically have the 4WD designation on the rear of the car body? I am completely confused by the designation 4X4 on some cars I have been shown. Any advice to this vehicularly challenged individual would be most appreciated.
  • wwestwwest Posts: 10,706
    The Highlander is NOT 4WD as defined by most knowing folks.

    The Highlander is F/AWD, and that for marketing purposes only.

    Note that there is a MYRIAD of F/AWD implementation methods out there in the marketplace, all with varying degrees of multi-wheel drive capability. The Acura/Honda SH-AWD system likely being the best of them, but in my opinion still inadequate for the conditions of travel you encounter.

    The Highlander uses three, front/center/rear, fully open differentials and would therefore be a 1WD vehicle were it not for the electronic braking capability provided by the TC, Traction Control, system.

    Many owners are already complaining that the TC system is totally inadequate for getting the vehicle unstuck, or even up and going on a slippery surface initially as long as TC is active.

    As a result some Toyota and Lexus F/AWD vehicles now have a TC disable function so the driver can use at least some level of wheelspin to get unstuck or rock back and forth to get unstuck. But one must keep in mind that with TC disabled you are back to 1WD.

    Toyota is also introducing a new form of TC called A-LSD, so far only installed on RWD or R/AWD vehicles, and apparently only activated if primary TC is disabled. A-LSD stands for Automatic Limited Slip Differential.

    It has always made sense to have LSD for a rear differential but somewhat hazardous, absent some driver familiarization training, for implementing at the front differential.

    IMMHO the vehicle you're really looking for is the Toyota 4runner. The 4runner has RWD mode, AWD mode, and most importantly for those logging roads, TRUE 4WD/4X4 mode, capability.

    But the key question to ask those salespersons is if the front driveline can be locked, SOLIDLY LOCKED, to the rear driveline for travel on those several miles of logging roads in the wintertime, or MUDDY spring. And I would be sure, CERTAIN sure, that whatever vehicle you purchase also has some form of rear LSD.
  • The Sequoia 2008 seems to be able to fully lock the front to the rear. I saw the button in the Platinum I was in.

    As for the Highlander, I thought it had a viscous fluid unit between front and rear which automatically stiffens if there is a difference in speed. I would call this a form of limited slip and not 'open.'
  • wwestwwest Posts: 10,706
    The early RX300 AWD model did have a VC across the center diff'l but that design was dropped with the introduction of the RX330 series in '04 in favor of only the TC system for AWD capability. I understand it is the same for the HL and Sienna, at least the last I checked with the documentation at techinfo.toyota.com.

    Lexus.com still indicates the RX350 has a VC but the documentation indicates that it does not. I'm in an ongoing argument with Lexus customer service about this at this very moment.
  • It would seem like the auto-wheel-braking traction control combined with a front, rear, and center limited slip would be the single best system. That is what a 1999 and newer Hummer H1 uses. They use three Torsen diffs though I am not sure exactly which model Torsen.
  • nedzelnedzel Posts: 787
    I agree with wwest. The 4Runner has a far more sophisticated and capable AWD/4WD system than the Highlander and will do far better offroad and on bad logging roads than a Highlander.
  • wwestwwest Posts: 10,706
    If you have mechanical front/rear/center LSDs why would you even need auto-wheel-braking traction control..??
  • "If you have mechanical front/rear/center LSDs why would you even need auto-wheel-braking traction control..??"

    Because the LSD is not as good as a locking differential when there is zero traction such as when one tire is in the air.

    But if the car can detect that tire slipping and use the brake just on that wheel, it can force 100% of the torque to other wheels. This comes close to the performance of a fully locked differential.

    A LSD does not redirect all the torque, just some percentage of it.

    My 1997 Hummer H1 had all limited slip differentials and the instruction manual said that if one wheel was in the air, you could force it to not spin by applying the brakes. The Torsen diff would then act as a torque-multiplier and make the other tires overpower the brakes and move. In 1999 they improved this by having a computer just only apply brakes to the wheels actually slipping instead of all of them. They still kept the LSDs. As far as I can tell, it is the ultimate full time system and probably just as good as 3 locking diffs without having to turn them off on pavement.
  • naatz1naatz1 Posts: 187
    Interesting how I got to the RAV4 and this forum, clicking on an ad from Edmunds on a quiet Sat afternoon ...I'd watched this forum a bit last Spring as a current 01 Jeep owner thinking I would try a Toyota RAV or new Highlander to get better mpg. After research into Toyota 4wd last summer, yes the mpg was better but those 2 vehicles did not qualify to tow w/margin a 3000 lb boat (needing $800 tow hitch classII option), nor did their 4wd systems make me feel confident living in Minnesota backroads (where we are having an old fashioned 18" of snow in Dec winter so far). I did not fit in a 4 runner w/low ceiling height and despite me liking the retro FJ, one look of the wife convinced me it was too truckish for her, no Jeep Wranglers either.

    So we bought another new Jeep Grand Cherokee with true 4WD ie lo range & 6500 class4 towing. I'd thought about the new 08 Liberty but the JGC handled night/day better. I also liked the Commander but the 3rd seat was a joke. Yes the Jeep only gets 15 city/20 highway mpg ($300/year for gas than a Highlander or Rav6) but it has a lifetime drivetrain warranty and our 01 was very reliable .

    No debate on it's 4WD system either if you need true 4WD QuadratracII does it.
    See the Edmunds Gr Cherokee forum for info http://townhall-talk.edmunds.com/WebX/.eea4ead/1030 or http://www.wkjeeps.com/wk_4x4.htm
  • Interesting discussion as to how Toyota "AWD" works (I added the quotes because it seems their systems are more reactive than proactive). It does not inspire confidence.

    Does Toyota actually brake spinning wheels to improve traction from the remaining wheels, or do they cut engine power to keep the spinning wheel from spinning?

    But as I am considering a RAV4 "AWD" .vs. Subaru Outback AWD .vs. Subaru Forester "AWD" (that system's more reactive than the Outbacks'), some comments would be welcomed.
  • "Does Toyota actually brake spinning wheels to improve traction from the remaining wheels, or do they cut engine power to keep the spinning wheel from spinning? "

    The car brakes just the spinning wheel. It can also cut some engine power as needed, but the braking is what forces the torque to move through the diff to another wheel.

    I think my 1999 Mercedes SLK only cut engine power but I am not sure.
  • wwestwwest Posts: 10,706
    Since the front wheels are the primary drive I wouldn't be too sure just a single front slipping wheel would be braked. Differential braking at the front might result in such a great level of torque stear that thumbs and fingers might get bruised and maybe even broken.

    So if a front wheel spins/slips then both front brakes are applied and the engine is simultaneous dethrottled to prevent subsequent brake/rotor overheating and warping.
  • 2toyotas2toyotas Posts: 104
    Wwest if you look on techinfo.com under new features for 2007 RX350 you will see that the VC was added again for 2007. It was not added to the Highlander for 2008, which I do not understand why.
  • wwestwwest Posts: 10,706
    Toyota has renamed VSC/TC/BA/EBD/etc. to VDIM. Supposedly as a result of "tighter, closer system integration but I suspect more of a marketing move.
  • In my understanding Toyota 4WD system on HL, RAV, Siena, etc... never meant for true off road. These vehicles designed for city driving and most never in live drive off the pavement. Toyota 4WD system improves driving in snow or rain, and can get vehicle unstuck from the snow (you might need need to disable VSC in some cases but it will get you out of snow!). These vehicles have improved drive ability in poor weather conditions without sacrificing a lot in fuel efficiency comparing to "real 4WD".
  • Just bought a 2005 4wd Highlander from a dealer with Toyota Certified guarantee--covers drive train and major things for another 75k (Car has 23k) or 2015--whichever comes first. For $1700 I can purchase a warranty on a huge number of other things, including electronics etc (not tires and brake pads) I have to buy before I pick up the car (they are putting in some stuff) Anyone have an opinion as to whether I should purchase this "platinum" warranty? Or is it a scam? Opinions desperately welcomed! Thanks in advance.
  • wwestwwest Posts: 10,706
    Actually it's TC, Traction Control that might need to be disabled, but keep in mine that when you do that you end up with a "1WD" vehicle if on or in a slippery surface. VSC uses the brakes but only to prevent over or under stearing, plowing or skiding.
  • Right, this is TC. It only needs to be disabled on rare occasions when vehicle gets stuck in the deep snow. Enable it back once vehicle is out of it so you'll be safe on "slippery surface". I know that HL 4WD inferior to Jeep (that designed for off road in mind). I'll take HL 4WD gas savings over superior off road handling of a Jeep or a Hummer. I feel that for everyday commuting HL 4WD is overkill and even 2WD will get you safely anywhere.. I got 4WD more like additional safety feature in the family vehicle and it will serve that purpose.
  • wwestwwest Posts: 10,706
    Other than an actual transfer case in order to have a low, granny-grunt, gear range I'm not sure there is enough weight difference between the HL with only a PTO and a 4runner.

    Then there is the BMW X3/5 with REAL AWD, R/AWD.
  • bobwileybobwiley Posts: 241
    Check Crown Toyota in Topeka KS or Greenfield Toyota in MA--they offer "greatly discounted" Toyota Extended Warranty's. I'm not at home, so I can't get you ph #'s. In some of the other Toyota Forums they have the info. You can get a 100K 7 Yr Toyota Bumper to Bumper Warranty for about $990. In case you've already purchased it from the HIGH PIRICED dealer--you can still turn it back to Toyota for I think a $50 admin fee. Yes, it is the SAME warranty--the administrative office is in Cedar Rapids, Iowa. I know, I bought from the dealer and learned about the discounted waranty on this Forum. Very EASY process to get a discounted warranty. Look under the Toyota Avalon Forums--I know the reference is there for the dealers willing to discount. Find out the price and then negotiate with your dealer. The Finance guy is the one who gains on the deal!! Good luck!
    Bob
  • trebor129trebor129 Posts: 176
    Just pay for your own repairs. They obviously take in more money than they pay out. That is how they profit on it. What that means is that -- paying for a warranty is really a bad deal. Worst of all it adds nothing for the first three years so they just invest the money and try to grow it by the time they might have to pay.
  • lucky_777lucky_777 Posts: 205
    I paid $560 for 4WD HL 7y/75k Toyota platinum warranty with $0 deduct from Toyota Midwest superstore in Kansas back in September. Most likely I'll never use it but who knows...
  • "Just pay for your own repairs. They obviously take in more money than they pay out."
    Is a game of volume...like insurance. That's how they make money. If it makes you feel better having the added protection then by all means purchase the warranty. You probably have better than a 50% chance you'll use some or all of it and recoup your cost anyways.
  • harboharbo Posts: 136
    My opinion ...... if you run a 4WD and use it hard buy the extended warranty. If you run a 2WD mostly over the road, no need.
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