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Toyota 4WD systems explained

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Comments

  • hdfatboyhdfatboy Posts: 324
    "No input is needed/required if you believe the torque biasing is 50/50, we already understand the reasons for your position, understanding."

    And what would you say are the "reasons for my position"? Seems like you are really struggling with Toyota, not me. I don't have a position. To be honest, I really don't care whether a Highlander or RX, does or doesn't have a viscous ctr LSD. I have no interest in either of these vehicles from a personal perspective.

    I'm simply sharing the readily accessible information that Toyota makes available to the public. The readers can decide for themselves based on the sources I shared as to whether Toyota's formal press releases and product information brochures are more or less accurate than the source of the information you're basing your view on.... that's not available to the public (without a fee).

    For my money, I would go with the publicly available information from Toyota because I am very confident that these documents (particularly press releases) go through an extensive copy control process and legal review to avoid lawsuits. I also think that the tech files are likely to be somewhat behind the launch of a new product as all these vehicles are.

    If you're frustrated, and it sounds like you are, its not with me. It must be with Toyota. You seem to keep referring back to documents that concern 7 & 8 year old Toyota vehicles. All of my posts have been about 2008 Toyota and Lexus vehicles.

    Based on the information from Toyota's own publicly accessible website here's the facts as I read them. These facts apply to 2008 vehicles and 2008 only (although they may also be true for previous model years as well).

    08 RX AWD has a mechanical viscous center LSD combined with TRAC that delivers 50/50 fr/rr torque distribution that moves torque from this starting point to wheels with greater traction as needed.

    08 Sequoia, Land Cruiser and LX570 have a mechanical Torsen LSD differential that maintains a minimum of 40fr/60rr torque distribution until slippage occurs at which point power can be moved from the rear wheels to the front "instantaneously" (Toyota's words, not mine). Each of these vehicles also has a mechanically open rear differential.

    Toyota engineers view a mechanical Torsen LSD as superior to a "speed sensing" LSD (ie. e-LSD using electronic engine and brake management to simulate a mechanical LSD).

    These are simply statements of fact from Toyota's own publicly available and highly promoted documents (since much of the same information is in the promotional brochures for these vehicles). To the extent you disagree with these facts you're not disagreeing with me.... but with Toyota.
  • hdfatboyhdfatboy Posts: 324
    "Why would any manufacturer put a Torsen, Torque Sensing Differential, in what is basically a FWD vehicle to begin with?? "

    I'm not aware of any manufacturer that has applied a Torsen mech LSD to an AWD drivetrain for a vehicle that would otherwise have been a FWD vehicle. What manufacturer and vehicle are you talking about?

    "Oh, is there any such thing as a rear locking diff'l for this market segment. Drag racing or maybe other racing venues of maybe even serious off-road, but road going."

    What "segment" are you talking about? SUVs in general? Many of the GM full-size suvs have locking rear differentials standard (including the new Hybrid Tahoe) or offer them as an optional upgrade. If you're talking about smaller suvs, then the Porsche Cayenne is worth noting since it has a auto-locking rear differential.

    If you're referring to lower and mid-level SUVs (both size and cost) I'm not aware of any suvs that would have a locking rear differential since they aren't likely to have the power and torque to need or benefit from such a differential.
  • wwestwwest Posts: 10,706
    Techinfo.toyota.com NCF (New Car Features) documentation for the initial year for the RX350, 2007, indicates the VC was adopted (re-adopted??) in that model year by switching from the MF2A "transfer" used in the previous RX330 series, to the MF2AV for the new RX350. Addition of the "V" apparently meaning the incorporation of a VC.

    That is the SOLE and ONLY reference made to either viscous or MF2AV throughout the ENTIRE documentation set for the 2007, 2008, and 2009 model years of the RX350.

    On the other hand, when I searched for MF2A in the RX350 files for all of these model years, '07, '08, and '09, I had "hits" throughout the documentation sets indicating the continued use of the RX330's MF2A transfer, non-VC transfer system.

    And if you were Lexus, which group would you wish(***1) to "fool", the mechanics and technicians who are called upon to work on these vehicles on a daily basis, and more importantly understand, completely, the operational aspects of same.

    Or customers, apparently like yourself, that unquestioningly, or even not knowing or even being interested otherwise, follow the marketing "line".

    ***1: Over-stepping on my part, at least I like to think so. Just as quite clearly happened during the marketing rollout of the RX330, someone, somehow, mistakenly conveyed the idea that the RX330 had a VC. That was subsequently corrected for the marketing material for the subsequent years of the RX330's market availability.

    Methinks that somehow that same mistake was repeated for the marketing introduction of the RX350 and Japanese "culture" being what it is, no one is willing to step up and take on the responsibility for either admitting the mistake, nor correcting same. Everyone is in "heads down" mode.

    The way the material reads, and marketing being what it is(***2), it even seems like there is a possibility that Lexus at one time during the design phase of the RX350 intended to put the VC into the RX350. But undoubtedly some bright young engineer later pointed out that all that would do is add weight and cost to the product since the way TC operated the VC would never be functional.

    ***2: Product marketing materials must be made available for distribution months before the products reach the dealer showrooms. Clearly, even just days prior to actual production began for the RX350, the initial decision to incorporate the Mf2AV in teh design could have been revised to the MF2A. Since both the Highlander and Sienna continue to use the MF2A inventoried parts availability would not have been an insurmountable issue.
  • hdfatboyhdfatboy Posts: 324
    I think you're over-reaching to satisfy your personal belief. Is it possible that the RX manufactured in the US for the US market has a viscous ctr LSD and the RX made in Japan is made without the ctr diff for the ROW market?

    "And if you were Lexus, which group would you wish(***1) to "fool", the mechanics and technicians who are called upon to work on these vehicles on a daily basis, and more importantly understand, completely, the operational aspects of same. "

    I doubt that the website you're accessing is the only reference used by Lexus and Toyota mechanics for making repairs. IMO the site you're accessing is just another nice money making venture for Toyota to tap into a market of overly enthusiastic Toyota fans willing to pay $10/day to access a technical site that they probably only update a couple times a year at best. Do they even give you a "revision date" on the website your paying Toyota to access?

    "Or customers, apparently like yourself, that unquestioningly, or even not knowing or even being interested otherwise, follow the marketing "line". "

    My bet is that the information provided to the public is significantly more accurate then the website you're paying to access. Mechanics can't sue for false technical information. OTOH Consumers and State Attorney Generals are ALWAYS looking for a new deep pocket to go after. Whether its for personal wealth gain or media headlines, attorneys would chase a purposeful false advertising by a large corporation like Toyota like wolves chasing a lone sheep. A false claim on a high $ purchase like a vehicle would have either been addressed by an external attorney for a headline/$ or an internal attorney for a correction.

    You aren't by chance one of those "conspiracy theory" guys that think the US landing on the moon was all a hoax by the gov. ...are you? Sounds to me like an attempt to justify all the money you've spent accessing the Toyota technical site (aka Toyota's little "moneymaker"...I think they probably refer to it internally as their "100% profit margin" product with next to no upkeep or capital cost:))
  • wwestwwest Posts: 10,706
    http://www.4x4abc.com/4WD101/locking.html

    You aren't by chance...

    No, but I am quite quite thoroughly convinced that just as Harrison Ford says, he could do a STELLAR job as US President vs the IDIOT we now have.

    But I really do have to go now...

    This discussion has now become totally useless, even bordering on the nonsensical.
  • wwestwwest Posts: 10,706
    "The '08 Sequoia has a Torsen center differential with the power distributed 40/60."

    You might want to have a more thorough looksee at the 2008 Sequoia "Vehicle Inquiry Report" you posted at Carspace.

    It quite clearly states that your Sequoia has:

    A-TRAC

    Auto Lmtd Slip Diff,...

    Yes, "Auto Lmtd Slip Diff" does leave the door open to the possibility of that being a Torsen diff'l. But certainly that wording is not explicit enough to refute the information I have access to indicating that in H4F mode it is a simple open diff'l using A-TRAC for torque distribution. And if you are in of the firm belief that a simple open diff'l results in 50/50 F/R rear torque distribution how do you get that your Sequoia is 40/60..??

    Obviously in H4L or L4L there will be no "split" as the front and rear drivelines are mechanically "hard" coupled.

    Since you seemingly put more faith in marketing materials than actual facts here's one that supports your description of the '08 Sequoia 4WD but then goes on to say that the '08 also includes A-TRAC.

    http://www.jdpower.com/autos/articles/2008-Toyota-Sequoia-Preview

    Toyota's own definition of A-TRAC, ACTIVE-TRAC:

    http://www.toyota.com/help/glossary.html#a
  • wwestwwest Posts: 10,706
    Strange, now entering the TWILIGHT ZONE.

    The Traction Control documentation, A-TRAC, etc, at techinfo.toyota. com quite clearly indicates that in 2WD mode it is the front wheels that are being driven.

    I have always assumed the Sequoia to be RWD in 2WD mode.

    But.

    Why not FWD..? (I guess)
  • hdfatboyhdfatboy Posts: 324
    "You might want to have a more thorough looksee at the 2008 Sequoia "Vehicle Inquiry Report" you posted at Carspace."

    What on earth on you talking about? I've never made a post in the "Vehicle Inquiry Report".

    "It quite clearly states that your Sequoia has:

    A-TRAC"


    When did I ever say the Sequoia didn't have A-TRAC? It definitely has A-TRAC. As does the LC and LX570. A-TRAC is entirely compatibale and in fact functions better with a Torsen than with an open differential. A-TRAC is nothing more than the Toyota traction control software designed for 4wd vehicles. I'm familiar with the function as it's on my new Sequoia.

    You seem to be somewhat confused on the difference between the purpose of Traction and stability control software in the 08 4wd SUVs (A-TRAC & VSC) and the purpose of a mechanical LSD such as a viscous unit or a Torsen unit. The software is entirely complimentary to a drivetrain with a mechanical LSD. Have you not read any of the earlier posts? Subaru, GM, Audi, Porsche all use mechanical LSD combined with stability and traction control software.

    Toyota also includes mechanical ctr differentials on their 08 4wd 4Runner, 08 RX AWD, 08 4wd Sequoia, 08 4wd Land Cruiser, 08 LX570, 08 LS600h. Why would you think A-Trac couldn't be used with a mechanical LSD? Many manufacturers have combined the 2 technologies (Braking/engine management software + mech LSDs) for nearly a decade.
  • hdfatboyhdfatboy Posts: 324
    "Strange, now entering the TWILIGHT ZONE.

    The Traction Control documentation, A-TRAC, etc, at techinfo.toyota. com quite clearly indicates that in 2WD mode it is the front wheels that are being driven.

    I have always assumed the Sequoia to be RWD in 2WD mode.

    But.

    Why not FWD..? (I guess)"


    You're kidding ....right? I would definitely cease using the techinfo source as a reputable source if it shows the 2wd mode of a 4wd Sequoia operating as FWD.

    For the record, the 08 Sequoia is undeniably a RWD vehicle when operating in 2wd mode (identical to the LC and LX). Even you couldn't possibly think the Sequoia is a fwd vehicle. Just look at the driveshaft in a 2wd model for crying out loud and the available tow rating.

    If it were me, I would ask for my money back for accessing techinfo.toyota. You're definitely getting ripped off based on the very innacurate information you're posting.
  • wwestwwest Posts: 10,706
    "Why would you think A-Trac couldn't be used with a mechanical LSD...?"

    Maybe just because I'm NOT an IDIOT...??

    Certainly not on the scale of Shrub.

    With a Torsen center diff'l, say 30/70 F/R what additional capabilities would be added by including A-Trac....??

    And think back...

    It was with the introduction of the RX330 in 2004 equipped with "A-Trac" that the realization came, finally, that the VC was now useless, just added weight and was therefore a needless expense.

    And the last documenation I can find that indicates the 4runner, the LX470, and the Sequoia have, had, a Torsen center diff'l, just happens to be the 2003 model year.

    Why continue to purchase Torsen Diff'ls from Zetel, or even pay them a license fee, once you come to the realization that A-Trac will do the job at an acceptable level for the public at large...?

    And are you STILL of the mind that the GMC Denali series has a center mechainical LSD? You haven't had much to say on that front lately.
  • wwestwwest Posts: 10,706
    "..the '08 Sequoia is undeniably a RWD..."

    Are you certain sure..?? How, where does it say..??

    And just what general public owner would EVER notice, know, or care...??

    As you have said yourself, for only 2 wheels driving then FWD is better than RWD.

    If both drivelines are already in place just why would RWD be selected over FWD...??

    I grant you this is a really weird development....

    But...

    From techinfo.toyota.com '08 Sequoia:

    Active Traction Control (4WD)

    While driving in the 4WD mode, the active TRAC system helps control any wheel spinning which may occur when accelerating on a snowy road or during severe off-road driving, by controlling the brake fluid pressure of each wheel. The system distributes the traction which is lost to slipping to the other wheels, which produces a strong LSD effect. When the active TRAC is in use, the ABS and traction actuator assembly sends a signal and the slip Indicator in the instrumental cluster will flash to notify the driver.

    Active Traction Control Operation (2WD)

    The vehicle speed is estimated by taking the rear wheel speed, comparing it with the front, driving wheel speed and then judging the grip condition of the driving wheels. From this estimated vehicle speed, the target speed for the driving speed will be set. When the front, driving wheel speed exceeds the control starting speed, it judges that a tire slip is occurring and enacts the electronic throttle control and brake control and then attempts to make the rear wheel speed become the traction control target speed. The traction control will finish either when the vehicle moves onto a surface where the driving wheels do not slip or when the driver decelerates the vehicle.
  • hdfatboyhdfatboy Posts: 324
    "Why would you think A-Trac couldn't be used with a mechanical LSD...?"

    Maybe just because I'm NOT an IDIOT...??

    Certainly not on the scale of Shrub.

    With a Torsen center diff'l, say 30/70 F/R what additional capabilities would be added by including A-Trac....??

    And think back... "


    WWest...with all due respect....I have absolutely no idea what you're even talking about. Maybe others understand you but you seem to be alittle too off kilter for me to respond since you're not really making much sense. Maybe its just me...but I don't think so. Are you OK?

    "Why continue to purchase Torsen Diff'ls from Zetel, or even pay them a license fee, once you come to the realization that A-Trac will do the job at an acceptable level for the public at large...? "

    Clearly the engineers at some pretty reputable manufacturers like Audi, Subaru, GM and Toyota disagree with your POV, since they have combined mechanical LSDs with electronic traction systems. For me, its a great combination of technologies that puts more power on the road and still protects consumer from themselves. Sounds like you might consider a Highlander since you've already stated that it combines an open ctr differential with traction control software.

    By getting a Highlander you save money on buying a vehicle with a Torsen CTR and can use the savings for more access to Techinfo.toyota.

    "And are you STILL of the mind that the GMC Denali series has a center mechainical LSD? You haven't had much to say on that front lately."

    I think your memory is struggling abit as I referenced a number of times that the 2001 Denali XL sitting in my driveway has a mechanical ctr LSD (viscous) combined with a mech rear LSD.

    Here's Edmunds summary of the 2008 Denali XL which includes a "mechanical center differential " and a "rear locking differential". http://www.edmunds.com/new/2008/gmc/yukonxl/100894098/standard.html

    Here's Edmunds summary of a 2001 Denali XL (which matches the information in my manual and all the literature I have on the vehicle, but no...I'm not going to disassemble the differental in my driveway and take pictures so that you'll "believe"): "Limited Slip Differential (Center)" and a "Locking Differential (Rear)". http://www.edmunds.com/used/2001/gmc/yukonxl/100001202/standard.html

    Trust me....the US government really did really put a man on the moon.
  • wwestwwest Posts: 10,706
    " I have absolutely no idea what you're even talking about.."

    Yeah, I have noticed that.

    I'm in Seattle, you are...??
  • hdfatboyhdfatboy Posts: 324
    ""..the '09 Sienna is undeniably a RWD..."

    Are you certain sure..?? How, where does it say..??"

    Why are you posting false quotes? I did not make make the quote above. The Sienna is a FWD minivan. You either have me confused with someone else or you are purposefully fabricating false quotes.

    I'll leave it to the moderator to address if appropriate, however you are losing what little credibility you might have had with your inaccurate information and now fabricating quotes of others
    .
  • 2toyotas2toyotas Posts: 104
    hdfatboy

    If I were you I would stop answering him, for your own sanity. Believe me, Techinfo.toyota has all the right info, and it is nothing like what Wwest is posting. I think he is trying to egg you on. Good Luck!!
  • wwestwwest Posts: 10,706
    I just finished a brief review of the Edmunds threads, posts, concerning the GMC Denali 4WD implemenation. By about July of '03 the number of posts discussing the pros and cons of the OLD Denali LSD 4WD system vs the NEWER open center diff'l Traction Controlled 4WD systems are clearly available.

    Some of those posts are expressing concern about the rear mechanical LSD not being available as an option with the new braking implemented 4WD system.

    July of '03, now why does that seem to ring a bell...??

    Sorry about the '09 Sienna slip-up, I have corrected it.
  • wwestwwest Posts: 10,706
    Would you be so kind as to tell me, advise me, as to where I have quoted from techinfo.toyota.com something that is not there or is not true...??
  • 2toyotas2toyotas Posts: 104
    4WD SYSTEM
    1. General
     The 4WD model of the ’04 Highlander has discontinued the viscous coupling in the center differential.
     This system, which has adopted front and center differentials with bevel gears, employs TRAC control
    in order to ensure the proper drive when a wheel slips, without the use of an LSD (Limited Slip
    Differential) mechanism in the center differential. Thus, a lightweight system that offers high levels of
    driving stability and drivability has been realized

    This is the real 2004 Highlander New Car Features.
  • 2toyotas2toyotas Posts: 104
    4WD SYSTEM
    DESCRIPTION
     The 4WD model of the ’04 RX330 has adopted a full-time 4WD system that constantly distributes torque
    at a ratio of 50:50 to the front and rear axles.
     This system, which has adopted front and center differentials with bevel gears, employs TRAC control
    in order to ensure the proper drive when a wheel slips, without the use of an LSD (Limited Slip
    Differential) mechanism in the center differential. Thus, a lightweight system that offers high levels of
    driving stability and drivability has been realized

    This is the real 2004 RX330
  • 2toyotas2toyotas Posts: 104
    4. Transfer
    The engine type is changed from 3MZ-FE to 2GR-FE. Because of this change, an MF2AV transfer is adopted.
    The MF2AV transfer is similar to the conventional MF2A transfer, however, the MF2AV transfer contains
    a viscous coupling type LSD (Limited Slip Differential).
     The MF2AV transfer uses a viscous coupling to achieve the slip limiting effect for the center differential.

    This is for the 2007 RX350
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