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Toyota 4WD systems explained

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Comments

  • wwestwwest Posts: 10,706
    I'm going to stand by my statement, but let me first give you my definition of "tail-happy"...

    Tail-happy is when you are driving STRAIGHT along and step on the gas and the rear tries to get in the lead, very common to RWD. On the other hand, in your case. diff'l locked, if you happen to be turning at the same time then inertia comes into play and the rear end will skid toward the outside of the turn while the front plows to the same "degree".

    So your 4Runner, with the center diff'l locked, and equal tires on all four, will have neutral "happiness", just as the Toyota design engineers intended.

    I'm surprised at ABS, and TC, remaining enabled since BOTH drivelines MUST turn in synchronization and that compromises the functionality of ABS and TC.
  • nedzelnedzel Posts: 787
    wwest: I own a 4Runner. I have driven a 4Runner in the snow, with the center diff locked and unlocked. I have real, live experience with the vehicle. You have, what? Theories and supposition? Go drive one in the snow with the center diff locked and unlocked. Then come back and tell us about it. Until then...
  • wwestwwest Posts: 10,706
    "..go drive one in the snow..."

    How about miles upon miles on mountain passes in WA, OR, ID, and MT, more often packed snow than not. Except for those many early morning drives up the mountain in order to be the first to lay "tracks" in the freshly fallen snow.

    I can't imagine that the 4runner drive system and handling dynamics in various drive configurations would be that much different from my '85 Jeep nor my '92 Jeep, both Cherokee Limited's with RWD/"AWD"/4WD/4X4 modes. Maybe as much as 150,000 miles overall, and quite a few NW winters with Ski trips.

    The '92 is still doing duty in the "family" on a cattle and wheat ranch in north central MT.

    I admit I never found much, if any, use for the AWD mode, 4 wheels driven but center diff'l open, and I probably never found use for the 4-lo mode.

    But I did find lots of use for the 4WD (diff'l LOCKED) mode, often with rear chains installed and sometimes with all four chains.

    Oh, I always removed the ABS fuse during the summer.
  • greengreen Posts: 15
    "But as I said, the center diff'l should NOT remain locked once underway."

    You've repeated that idea, with emphasis, a few times (even branding it unsafe) so I'm curious to know your reason. I don't expect to hear anything I haven't heard, but your position seems to be even more extreme than the standard "NEVER lock on dry pavement" warning which is already over simplified, imo.
  • wwestwwest Posts: 10,706
    Once you're underway the usefulness of the extra "drive" traction is mostly negated by momentum. You may also note that with more modern 4WD systems the ABS & VSC are disabled in 4WD mode. In some cases 4WD mode itself is disabled if you apply the brakes or if VSC activates. Traditional 4WD systems use a spline or dog clutch which cannot be quickly, reliably, disenaged, so these "features" are kept disabled.

    Leaving a 4WD system engaged once underway is a lot like driving a FWD, or F/awd, patently UNSAFE. On an adverse condition roadbed, slippery roadbed, it is highly desireable to dedicate the front tire traction solely to directional control. With a locked center diff'l 50% of the engine drive torque, or ~70-80% of engine compression braking, is applied to the front wheels, leaving not much of the already low front traction coefficient for maintaining directional control.

    IMMHO the best feature of ANY AWD system would be to remove all engine leading or lagging torque from the front tires as soon as the stability control system indicates a yawing condition, the vehicle is NOT following the "line" set by the stearing angle of the front wheels.

    There is as yet, to my knowledge, NO FWD based AWD system that can accomplish that task.

    The best "simulation" is to put your "traditional" 4WD system into RWD mode.
  • greengreen Posts: 15
    Thanks for the reply.
  • nedzelnedzel Posts: 787
    wwest, so, in other words, you haven't driven a 4Runner in the snow. Go drive one and then get back to us.
  • wwestwwest Posts: 10,706
    Assuming 4 good tires in both cases, what makes you think there is something to be learned driving a 4runner vs the years and miles, snow and ice miles included, spent driving the RWD/4WD(AWD)/4X4 Jeeps...??

    Granted, the 4runner's AWD mode, 30/70 F/R torque distribution offers additional capability over the Jeeps, but then I get to throw in my years and miles, again with snow and ice miles, in my '94 AWD Ford Aerostar, 30/70 F/R unless slippage at the rear occurs in which case it goes to 50/50 for the next few minutes.

    And if you happen to be bringing up the TC/VSC capabilities of the 4runner, NOTHING beats the PSM in my 996 C4 in that category.
  • nedzelnedzel Posts: 787
    WWest, in the winter I run snow tires on the 4Runner. I have four Nokian Hakkapeliitta snow tires, all with good tread.

    I've driven the 4Runner in snow, with and without the center diff locked. You haven't. You can speculate and theorize about how you think it should handle in the snow, but you haven't driven it. I have. So please stop telling me about how it handles. I know how it handles. You don't. You haven't driven it.

    I won't speculate about how your Jeeps, with different drivetrains, different suspensions, and different weight balances, handle in different conditions and different 4WD/AWD modes. You've driven them. I haven't.

    Feel free to brag about your 996. I'm sure it is a very lovely car. But I fail to see how that is germane to how a 4Runner handles in the snow with the center diff locked.
  • wwestwwest Posts: 10,706
    The 911 isn't germane to driving the 4runner with the diff'l locked, only unlocked with VSC and ABS enabled.

    "...please stop telling me how it handles..."

    We seem to have off-track pretty much solely on the issue of your 4runner being "tail-happy" with the center diff'l locked. Frankly I think anyone of actual knowledge or long experience will tell you that should NOT happen.

    But again, just what is your definition of "tail-happy"...?

    Mine would be: "f you step on the gas traveling straight down the road the engine torque applied to the rear will often result in the rear trying to lead the front. Pretty much SOP for RWD or R/awd but IMMHO NEVER in 4WD with the center diff'l locked.

    Have you had a mechanic check and certify that your 4runner really does have the center diff'l LOCKED when the indication lights up...??
  • wwestwwest Posts: 10,706
    Maybe I see..

    With the center diff'l locked ABS is disabled and since frictional braking is ALWAYS biased toward the front your 4runner will have a strong tendancy for the rear coming "about", especially when "braking" while traveling downhill. To some extend engine compression braking will have the same effect.

    Your 4runner is not necessarily any more tail-happy with the diff'l locked than any other non-ABS equipped vehicle, RWD/FWD, etc, etc.

    Yet another reason for NOT using the locked mode once underway at a decent speed.

    One of the more common hazards, inadvertent engine "braking" of FWD and/or F/awd vehicles.
  • 2toyotas2toyotas Posts: 104
    Nedzel, You will never win with Wwest. He still does not know that all toyota SUV,s, and trucks keep ABS and traction control active when in 4 locked mode. even in my tundra, which is part time 4wd, Traction control and ABS works when locked in 4WD. On new Tundras you can keep VSC active when in 4 locked. You are wasting your time because Wwest keeps arguing his point whether he is right or not. Just look at some of are previous posts. I gave up.
  • wwestwwest Posts: 10,706
    When the center differential is locked the front and rear drivelines MUST turn at equal rotation. Even if ABS were left enabled, which I do not believe, it could not be fully functional. The same goes for VSC. How could VSC apply differential braking, something it is often required to do, in the rear vs the front vs if the driveline has them locked together, braking the rear would automatically be "reflected" at the front.

    The 2009 4runner owners manual indicates that VSC is disabled when the center diff'l is locked. Could find no reference to ABS one way or another.
  • Beginning with the 2000 model year Land Cruiser, Toyota began using a new 4WD system called ActiveTrac. This same system was incorporated into all 2001 4Runners and the new 2001 Sequoias. The same basic system has also been used in the Mercedes M Class as well as post ‘99 Humvees. :(
  • nedzelnedzel Posts: 787
    "With the center diff'l locked ABS is disabled and since frictional braking is ALWAYS biased toward the front your 4runner will have a strong tendancy for the rear coming "about", especially when "braking" while traveling downhill. To some extend engine compression braking will have the same effect. "
    Actually, I experience it under heavy acceleration, in snow, with the center diff locked.
  • steverstever YooperlandPosts: 40,206
    (cross-posted to 4WD & AWD systems explained)

    "it looks like Toyota has given the Trail Grade 4Runner as much four-wheel-drive capability as anything else sold in the U.S, giving Toyota the widest and deepest range of serious 4x4s (FJ, 4Runner, Land Cruiser) in the industry."

    Is the 2010 4Runner Trail Grade the Best 4x4 Package Sold in the U.S.? (Straightline)

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  • nedzelnedzel Posts: 787
    Unfortunately, there is a very serious error that article. Only the Limited model comes with the Torsen center diff. The SR5 and Trail Editions do not have a center differential. You can see that in the document released by Toyota: http://pressroom.toyota.com/pr/tms/toyota/document/2010_4Runner_Product_Info.pdf- ?ncid=11092

    What this means is that here in the Northeast, when roads go from dry to wet to snow covered and back in just a few hundred yards, you can't use 4WD in the SR5 and Trail Editions. Not good, a big step backwards from the 4th Generation, and a huge disappointment.

    Steve, I hope you will ask the author of that article to contact Toyota to clarify that the Torsen center diff is not available on the SR5 and Trail editions, and then have him clarify the article explaining the implications. As it is, the article is very misleading.
  • steverstever YooperlandPosts: 40,206
    If you got my email, you know that I forwarded your comments to editorial.

    Sometimes manufacturer brochures are wrong and sometimes the "official" information contradicts itself. Press releases are notorious for getting things screwed up too.

    I'm curious to see what the story is here.

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  • i'm a mainer and currently own a 2006 V8 4runner (full-time 4WD) which is indispensable during the winter... i'm VERY interested to know what the reality is with the new 4runners' (lack of?) center differential (SR5 and Trail Edition) and if the 4WD can be used on-road... i've literally been waiting to buy the Trail Edition, but if it's going to be less sure-footed than my current 4Runner from December - April (yeah, that's almost half the year) i don't think i'll getting a new Toyota. :(
  • steverstever YooperlandPosts: 40,206
    Here's another Toyota press release:

    "SR5 and Trail 4x4 models have a two-speed lever-operated, part-time system with neutral position, while the 4Runner Limited is equipped with full-time, four-wheel-drive with a locking center differential and employs a three-mode, center console-mounted switch. The new 4Runner is also equipped with a stronger rear differential over the previous model, thanks to a gear ring that has increased in size from 7.87 to 8.18 inches.

    To enhance grip, the A-TRAC system is now standard equipment on all 4x4 models. The system can distribute driving force to any one wheel in contact with the ground, making terrain irregularities and slippery patches transparent to the driver. An electronic-locking rear differential is standard on the Trail grade. Axles house 3.73 gears, or 4.56:1 with the 2.7-liter engine and the differential housings have improved seals for better resistance to mud and water.

    Toyota’s Crawl Control (CRAWL) feature is standard on the Trail grade. CRAWL is an adjustable electro-mechanical system that can be tuned to match the terrain by selecting any of five speed levels. The system maintains an appropriate speed that keeps the vehicle under control and minimizes the load on drivetrain and suspension components. The CRAWL feature helps make traversing difficult terrain easier and safer. With the transfer case shifted into low range, Crawl Control regulates engine speed and output (along with braking force), to propel the vehicle forward or in reverse at one of the five low-speed settings. This allows the driver to maintain focus while steering over very rough level ground or steep grades, without having to also modulate the throttle, or brake, pedals.

    The Trail grade also features a Multi-Terrain Select system which allows the 4x4 operator to dial in wheel slip control to match the terrain. In loose terrain such as mud and sand, more-than-normal wheel slip is permitted, allowing wheel-spin to work in the vehicle’s favor. On bumpy moguls, or solid rock, wheel slip is minimized and the system acts more like a limited slip. The Mogul setting is for any extremely uneven terrain, such as V-ditches, slopes, and ridges, uphill or down."

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  • nedzelnedzel Posts: 787
    Sometimes manufacturer brochures are wrong and sometimes the "official" information contradicts itself. Press releases are notorious for getting things screwed up too.

    I'm curious to see what the story is here.

    Yup, I understand that. I, too, am curious to see what the story is here. But from what I've seen, in the Canadian market all trim lines get the Torsen center diff, while in the US only the Limited trim gets the Torsen center diff.

    I hope that I'm wrong and your editor is right. But I'd really like to see some clarification from Toyota.
  • steverstever YooperlandPosts: 40,206
    Poutine, Nanaimo bars, standard heated seats and Timmys....

    Canadians get all the good stuff. :-)

    But my guess is that Toyota didn't screw up the specs you listed or the press release though. :(

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  • nedzelnedzel Posts: 787
    That's my guess as well. Darnit. A Trail Edition with heated seats and a lockable Torsen center diff might be right up my alley.
  • nedzelnedzel Posts: 787
    I'm right there with you Steve. Here in New England, I won't buy a car without heated seats.
  • nedzelnedzel Posts: 787
    The 2010 4Runner SR5 and Trail Edition do NOT have a Torsen center differential. They have the VF2A transfer case. In other words, it is a part-time 4WD system that is not suitable for use on the road. Offroad only.

    This is a major step backwards for the 4Runner.
  • wwestwwest Posts: 10,706
    Don't be so quick..!!

    The shop manuals still show a "Torsen" type diff'l, perhaps a "clone" design (patent has run out..??) and not allowed use the "Torsen" name.
  • steverstever YooperlandPosts: 40,206
    Source for your confirmation? Thanks.

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  • wwestwwest Posts: 10,706
    As of 2010 the 4runner can be ordered with a simple transfer case, PART-TIME 4WD, or with the Torsen, FULL-TIME R/AWD or PART-TIME selectable mode.

    "...But..., frankly my dear, I don't give a damn!..."

    Can someone tell me, PLEASE tell me, why full-time AWD/4WD is so all-fired desireable..??

    IMMHO an IDEAL AWD system would be predominantly RWD and only couple drive torque to the front if the rear wheels begine to slip/spin. But in NO case should the front wheels be "driven", leading or lagging, with the brakes applied, in a tight turn, a low speed accelerating turn, or if should VSC activation be required.

    The only full-time AWD that comes even close to that is the Acura SH-AWD system.

    Think about it, if your vehicle has TC/TRAC, Traction Control, of what use is full-time AWD/4WD...?? Unless you have turned it off then the instant wheelspin/slip is detected TC will INSTANTLY moderately brake the slipping wheel(s) and just as INSTANTLY dethrottle the engine.

    Yes, you could now turn TC off, but I would just as soon be in the TRUE 4runner and switch to a LOCKED center diff'l/transfer for teh duration of travel on the slippery surface.
  • wwestwwest Posts: 10,706
    "...not suitable for use on the road.."

    Methinks you overstate slightly.

    The VF2A transfer will be perfectly fine, quite acceptable, for those of us that must content with wintertime adverse ROADBED conditions. And maybe an occassional venture off-road to get around all the FWD and F/awd either wrecked, stuck, or just simply stalled in the roadway.
  • nedzelnedzel Posts: 787
    wwest, I've already explained it quite well, and will not continue any conversations with you as long as you continue with that sort of tone. If you wish to have a civilized conversation and leave behind your all caps and eye-rolling and mocking and sarcasm and arrogance, fine. Until then...
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