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Toyota 4WD systems explained

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Comments

  • kurtamaxxxguykurtamaxxxguy Member Posts: 1,798
    To recap, 2toyotas, how does the RAV4s' 4WD system work?
    Is it similar to the 4runner?
  • nedzelnedzel Member Posts: 787
    "The new system in the 2008 LC, Sequoia, LX570, 4Runner and LS600h uses a mechanical LSD for the center differential which is not the case in the 4wd systems of Toyota's lower priced vehicles or last year's models.

    This newer system does not exist on most of their older models (I think it was on the older 4Runner models)."

    All of the 4th generation 4Runners (from 2003 on) have a lockable Torsen center differential. The same is true of the GX470. I believe that the previous generation LandCruiser and LX470 also used the same lockable Torsen center diff.
  • nedzelnedzel Member Posts: 787
    No, it is NOT similar at all to the 4Runner. The 4Runner has a lockable Torsen center differential and a low-range. The RAV4 is a FWD vehicle until the rears slip...
  • hdfatboyhdfatboy Member Posts: 324
    2toyotas,
    Exactly what references did I make that were incorrect? I stated that the 4Runner had a Torsen Center differential prior to 2008. According to Toyota's press releases on the '08 Sequoia, the Torsen Center Differential was added to the Sequoia this year. I would welcome any information suggesting the Sequoia had a Torsen Ctr Differential since 2005 as I have been unable to find such information.

    I made no reference to ALSD or TRAC. I simply stated that the Toyota system does not transfer torque across the rear axle upon slippage above 35mph. This is an accurate statement however I would again welcome any resource you have suggesting otherwise.

    The addition of the mechanical center differential to the Sequoia, LX570, Land Cruiser and LS600h are an acknowledgement by Toyota that it is a better system than they used in the previous year's 4wd system. Why do you suppose they added a mechanical center differential when most of Toyota's 4wd systems have had open diffs in the front, center and rear prior to 2008? It clearly is a more expensive design however its also a better design for on-road 4wd operation.

    I'm quite familiar with the system in the Sequoia and I believe the '08 design is a far better system than the previous design. The fact that the new system maintains a variable but minimum amount of torque to the front wheels when in 4wd hi (center diff unlocked) is only possible because they added the Torsen Center Differential which did not exist on any other vehicle in the Toyota lineup prior to 2008 (other than the 4Runner). This "AWD" mode with a minimum amount of torque always going to the front wheels could not have been achieved without a mechanical center differential.

    My point regarding the new Toyota 4wd design was specific to on-road traction and that most of the top-line brands have had a mechanical center differential for years. Toyota's addition to the list is a good thing. For the same reason they added a mechanical center diff to their system, I wish they had also added a mechanical limited slip diff to the rear. As I shared earlier, most if not all of the major brands include a limited slip differential on the rear of their higher end 4wd vehicles. Most engineers consider a liquid viscous diff., mech. LSD and electronically locking rear differentials as all being superior to an open differential with TRAC or any other type of system that utilizes the braking system solely to distribute torque.

    I would much rather have a system that starts with a mechnical LSD and fine-tunes traction with an electronic reverse braking system such as ATRAC. Toyota added a mechanical center differential because with the 5.7 they have added 105hp to the Sequoia/LX570/LC drivetrain that did not exist in prior years. Trying to manage over 400ft/lbs of torque with an electronic system is not practical which explains Toyota's conversion to a system used by most other brands. I just wish they had taken it to the next step and added a second Torsen to the rear differential.

    BTW, I hope your appraisal of the Sequoia's ability to "go farther without getting stuck" is accurate as I just ordered a Black/Red Rock Platinum Sequoia with delivery expected in early Feb.

    Here’s an interesting video on the rear differential and A-LSD in operation on the 2wd Tundra as compared to a 2wd Chevy with a locking rear differential. Its an exaggeration to some degree however it does highlight the limitations of a rear open diff with A-LSD vs a mechanical locking rear diff.
    http://www.youtube.com/watch?v=Z8PpZF77tgk

    Here’s the press release on the new Sequoia drivetrain.
    http://www.pressroom.toyota.com/Releases/View?id=TYT2007110908452
  • hdfatboyhdfatboy Member Posts: 324
    Based on the recent announcements from Toyota, the Torsen center diff has been newly added to the LX570, Land Cruiser, Sequoia and LS400h for 2008. The LX570, LC and Sequoia had (lockable) open center differentials prior to 2008. If anyone can provide a resource suggesting these vehicles had mechanical center LSDs before 2008...please share. (The only Toyota vehicle I have found information on that included a lockable center Torsen LSD prior to 2008 is the 4Runner).

    Prior to 2008 the Sequoia, LC and LX470 had locking center differentials, however when the ctr diff was unlocked it was essentially an open diff. This design is significantly different from the 2008 design which is a locking design that still retains a limited slip capability when it is unlocked.

    2008 LS400h http://pressroom.toyota.com/presstxt/2008lexuskit/2008LS600hL_sf.pdf
    2008 Sequoia http://www.pressroom.toyota.com/Releases/View?id=TYT2007110908452
    2008 LX570 http://jalopnik.com/336324/details-out-for-2008-lexus-lx-570-ndash-the-classy-wa- y-to-overcompensate
    2008 LC http://www.caranddriver.com/previews/14080/first-drive-2008-toyota-land-cruiser-- high-tech-suspension-page3.html

    Here’s a technical paper from Toyota on why they designed LC 4WD transfer case – VF4AM - for 2008 to incorporate a Torsen-C limited slip differential. This is the same transfer case used in the Sequoia, LX570 and LC. I believe the LS400h and the 4Runner use a different center Torsen unit from the 2008 LC, LX570 and Sequoia. As outlined in the article, the previous LC had an open center differential and relied solely on A-TRC for front/rear torque distribution. The article points out that traction is enhanced when A-TRC is used in combination with a Torsen differential. This means that torque transfer has been improved when transferring front to rear with the new design. Unfortunately it also means that the current design with an open rear diff using only A-TRC is not as good at transferring torque from left to right compared to a system that would have combined a Torsen rear diff with A-TRC.
    http://www.cuneoclub4wd.it/fram1/rubriche/toyota/toy2/trasmissione.pdf

    A Torsen rear diff would have added cost but would have resulted in a better 4wd system for on-road use. Namely… 2sp transfer case + lockable Torsen Ctr Diff. + Torsen rear diff. + A-TRC. The Chevy system includes the 2sp transfer case + lockable torsen ctr diff + auto-locking rear diff + electronic traction control. IMO the Chevy design is still a somewhat better 4wd setup for flexibility and road use, however the new Toyota 4WD system is definitely better than the prior year’s models used in the LC, LX470 and Sequoia with open center differentials (as their own technical paper confirms).
  • trebor129trebor129 Member Posts: 176
    The 1997 and newer Hummer H1s have 3 LSDs *and* also have an electronic slippage and wheel braking system. This sounds like the ultimate in design.

    Toyota claims having an open diff front and back is more reliable as LSDs fail more often. Perhaps, or perhaps it was just to save money.

    I would like to have 3 Torsen units. Torsen is a family of systems and you can get them in various designs with different behaviors.

    We had 6 inches of snow yesterday and I tested the new 2008 Sequoia up our driveway. Our 2006 Honda minivan cannot get up it. The Sequoia had a lot of trouble in 2WD mode but I could probably get it up with skill and momentum.

    I could detect no difference in performance between 4WD and 4WD with the center-diff fully locked.

    I also tried to wiz around corners on icy roads and also doing hard braking while turning, and the truck never spun out. I think that was the stability control working. I unfortunately did not try it with it turned off.
  • hdfatboyhdfatboy Member Posts: 324
    I've had 4 vehicles with mechanical rear LSDs. Each of these vehicles were driven between 80K & 120K miles. I've never had a failed mechanical LSD and never had to have any service work to them. There is no scheduled maintenance on any mechanical LSDs in the Chevy line-up for 100K miles. I've also never even met anyone that's had a failed LSD or heard of anyone with a failed mechanical LSD although I'm sure it has happened,

    While I'm confident the failure rate of a LSD is higher than an open diff, I believe failure of any modern differential is nominal when used in normal road conditions (not off-roading, snowing plowing or extreme towing).
  • wwestwwest Member Posts: 10,706
    "....*and* also have an electronic slippage and wheel braking system."

    Does it make any sense to have both? I would think the virtaul (braking) LSD would be so quick acting that a mechanical LSD would NEVER come into play...

    When a manufacturer says a vehicle has LSD but doesn't define the type how do you know which it is?

    Spring-loaded friction clutch pak?

    Viscous fluid?

    Torsen?

    Electronic via brakes?

    Not talking LOCKING diff'l here, only LIMITED slip.
  • wwestwwest Member Posts: 10,706
    For probably 99% of owners a rear LSD could fail and they would never know, notice. Maybe even greater than 99% since you have to have a need for a rear LSD in order to notice it isn't working and just how often does the average owner really NEED a rear LSD..??
  • 2toyotas2toyotas Member Posts: 104
    In 2005 the Sequoia began using the VF4AM transfer case which was already used in the V6 4Runner since 2003. It has a torsen center differential. I get my info from techinfo.toyota.com. It will cost you 10.00 to view, or you can just trust me.

    The traction system transfers power across the axle at any speed, it is TRAC in 2WD, and ATRAC in 4WD. ALSD only operates in 2WD and that turns off at 35mph, and then TRAC operates at any speed.

    I agree the torsen in the center is an improvement.

    The torsen splits power 40% front and 60% rear for normal driving in AWD mode. That is not minimum to the front.

    Have you ever driven a Toyota with ATRAC in bad weather or off road? I had an 05 Tundra with a limited slip rear diff, and in 4WD with the center diff locked in the snow the truck was good, I then traded it for an 06 with ATRAC, and it is much better than the 05 in snowy and even wet weather. ATRAC works so fast there is no need for a limited slip diff on the rear.
  • hdfatboyhdfatboy Member Posts: 324
    "When a manufacturer says a vehicle has LSD but doesn't define the type how do you know which it is?"

    In my reading on the subject, when detailed specs are provided, a manufacturer referring to a LSD diff is "generally" referring to a mechanical diff. This could be a viscous liquid, clutch plate type or Torsen. Most articles don't go into details since the vast majority of the public doesn't know the difference or for that matter care.

    No manufacturer I've read refers to their open diff with electronic brake control of slippage as a LSD. Generally they will have some hi-tech branded name by the manufacturer that refers to their reverse ABS software designed to control slippage. The one exception has been Toyota which refers to their system as A-LSD. In reality the name is a misnomer since the differential plays no role in determining how much/little slippage there is in the Toyota design since its an open design. Its my belief, that Toyota has used the term to give their consumers the sense that their electronic approach is equivalent to a true LSD. In my opinion, it is not equivalent and it would appear that Toyota's engineers agree with me based on the Toyota technical paper I provided earlier.

    Conclusion...while I'm sure there may be exceptions, for the most part when a manufacturer refers to their center or rear diff as an LSD, it most likely is a mechanical type. The exception would be Toyota that refers to their electronic approach combined with an open diff as A-LSD.
  • trebor129trebor129 Member Posts: 176
    LSD means 'limited' slip. It does not stop all slip. So yes, electronic braking system is a benefit because it can stop all slip.
  • hdfatboyhdfatboy Member Posts: 324
    "For probably 99% of owners a rear LSD could fail and they would never know, notice. Maybe even greater than 99% since you have to have a need for a rear LSD in order to notice it isn't working and just how often does the average owner really NEED a rear LSD..??"

    You would not want to drive with a failed LSD. It would make quite a racket after it fails.

    As evidenced by the many manufacturers that include a LSD in the rear of their drivetrain, I think its safe to say that it offers a significant benefit to most drivers that experience slippery on-road conditions on a regular basis. Based on Toyota changing the design of the 4wd drivetrain to include a center LSD after years of an open center design, I think Toyota would agree that an LSD is with A-TRC is a superior design to an open diff with A-TRC.
  • hdfatboyhdfatboy Member Posts: 324
    "LSD means 'limited' slip. It does not stop all slip. So yes, electronic braking system is a benefit because it can stop all slip."

    I agree with "Limited". I agree with "Slip". I disagree that their system has anything to do with the "Differential" in LSD. If Toyota had called it "Limited Slip Drive" or "Electonic Limited Slip" or "E-LS", I'd have no issue. It just technically is not a limited slip differential and any reference to the "differential" in their terminology is incorrect at least from a design perspective. I view it as an attempt to mask the fact that the rear differential is a basic open design.
  • hdfatboyhdfatboy Member Posts: 324
    "In 2005 the Sequoia began using the VF4AM transfer case which was already used in the V6 4Runner since 2003. It has a torsen center differential. I get my info from techinfo.toyota.com. It will cost you 10.00 to view, or you can just trust me."

    Actually the VF4AM transfer case with a Torsen-C center differential is new for 2008 in the Sequoia, LC, LX570. The addition of the Torsen-C center differential is what makes it unique from past applications in the Sequoia. The VF4AM has been used in the v6 4Runner since 2003.
    http://www.toyota120.com/GenDocs/2003_4Runner.pdf

    The v8 4Runner used the VF4BM transfer case. More details in the article below.
    http://www.vibratesoftware.com/html_help/html/Toyota/Toyota_Transfer_Units.htm

    Here's additional information on the older style VF4BM transfer case that was used in the previous gen Sequoia and 4Runner.
    http://youronlinemechanic.com/2007/09/28/vf4bm-transfer-with-torque-sensing-type- /
  • 2toyotas2toyotas Member Posts: 104
    You keep giving the wrong info, and I will keep correcting you. The VF4AM is used on the V6 4Runner and 05 - 07 Sequoia. The VF4BM is used on V8 4Runner and FJ Cruiser with a manual transmission. The 08 Sequoia uses the JF3A transfer case, and the Land Cruiser/LX570 uses the JF2A transfer case. All four have a torsen center diff., the difference being that the VF4AM and the JF3A have a 2WD option.

    You keep talking about ALSD as toyotas system. It is just a function of TRAC. You would only use ALSD if you needed rear wheel spin in 2WD when stuck, because TRAC would cut some engine power in addition to braking the spinning wheel. Once you are moving you wouldn't want ALSD on you would want TRAC on to keep stability.
  • hdfatboyhdfatboy Member Posts: 324
    2Toyotas,

    "You keep giving the wrong info, and I will keep correcting you. The VF4AM is used on the V6 4Runner and 05 - 07 Sequoia. The VF4BM is used on V8 4Runner and FJ Cruiser with a manual transmission. The 08 Sequoia uses the JF3A transfer case, and the Land Cruiser/LX570 uses the JF2A transfer case. All four have a torsen center diff., the difference being that the VF4AM and the JF3A have a 2WD option."

    I'd like to recommend that you take the time to read the source information I shared before suggesting I'm wrong in my statements. The Toyota information I provided above and that I will share again clearly states that the Sequoia through 2007 used the same transfer case as the V8 4Runner...namely the VF4BM transfer design. Here's the specific link again. If you believe you are correct and Toyota is wrong, let me suggest you contact them.
    http://www.vibratesoftware.com/html_help/html/Toyota/Toyota_Transfer_Units.htm

    According to all the information available that I have read... the Sequoia, LC and LX570 drivetrains were updated to include the Torsen-C center differential in 2008. Here’s Toyota’s press release for the new LC describing the “newly developed transfer case with a Torsen center differential”. http://www.zercustoms.com/news/2008-Toyota-Land-Cruiser-in-Japan.html

    All information prior to 2008 on the Sequoia describes an open center differential that can be locked by the driver. There is no reference anywhere I’ve searched that would show that the Sequoia had a lockable mechanical center LSD prior to 2008.

    Its interesting how I provide resources for my comments and yet your assertions are based on "trust me because I know more". I welcome the opportunity to learn and if the information and resources I shared are incorrect, it might be best to share a source, any source, that can support your claims.

    Please share any link that shows the Sequoia had a center Torsen LSD (4wd models obviously) prior to the new 2008 models as I've been unable to find any information that would support your claim. I'm confident that the center differential of the Sequoia is not a National Security issue and therefore if prior year models included a mechanical center LSD, it should be readily available on the internet. Perhaps I'm looking in the wrong places. I would welcome a link to any source suggesting the Sequoia had a Torsen center LSD prior to 2008.
  • trebor129trebor129 Member Posts: 176
    "I agree with "Limited". I agree with "Slip". I disagree that their system has anything to do with the "Differential" in LSD. If Toyota had called it "Limited Slip Drive" or "Electonic Limited Slip" or "E-LS", I'd have no issue. It just technically is not a limited slip differential and any reference to the "differential" in their terminology is incorrect at least from a design perspective. I view it as an attempt to mask the fact that the rear differential is a basic open design.

    I disagree because the Toyota system can apply brakes to just the slipping wheel. Since there is a constant amount of torque going to both wheel, braking one wheel has the effect of sending power (power being torque * rpm) through the open diff to the non-slipping wheel. So they are using electronics to make the open diff behave as an LSD. So calling it an electronic LSD "system" is fair.

    That being said, it has disadvantages to a mechanical LSD in that slip has to occur before it goes to action. A mechanical Torsen system can redirect power before slipping occurs. That is why a combined system, like the 1997 and newer H1, is better.
  • 2toyotas2toyotas Member Posts: 104
    http://www.tundrasolutions.com/forums/sequoia/29500-2005-sequoia-first-looks/

    You will clearly see the transfer was changed to the VF4AM which includes the torsen. This info is directly from toyota, your page is not. How can the Sequoia have the same transfer case as the V8 4Runner? The V8 is Full Time 4WD, and the Sequoia has a 2WD option? The VF4BM does also have the torsen in the center diff though. If you spend 10.00 for a day and go on techinfo.toyota.com which is also a toyota site, you can see all the features and how they work. I am not trying to go back and forth with you, but I will make sure you post the correct info. It is not fair to give people the wrong info about a vehicle.
  • 2toyotas2toyotas Member Posts: 104
    1. General
     The ’05 Sequoia uses the multi-mode VF4AM transfer.
     Along with the adoption of the VF4AM transfer, the transfer lever has been discontinued. Thus, in the
    4WD mode, the driver operates the 4Lo switch to switch between Lo and Hi.
     The VF4AM transfer is already in use on the ’04 4Runner with the 1GR-FE engine. For details on the basic
    construction and operation of the VF4AM transfer, see the ’03 4Runner NCF (Pub. NoSpecifications 
    Model ’05 Sequoia ’04 Sequoia
    Engine Type 2UZ-FE 
    Transfer Type VF4AM VF3AM
    Drive Type Multi-mode
    (Part-time & Full time) 
    H2 1.000 
    Gear Ratio H/H4 1.000 
    L/L4 2.566 
    Reduction Gear Type Single Pinion Planetary 
    Center Differential Gear Type TORSEN LSD*2 Double Pinion Planetary
    Oil Capacity
    Liters (US qts, Imp.qts) 1.4 (1.5, 1.3) 1.2 (1.3, 1.1)
    Oil Viscosity SAE 75W-90 
    Oil Grade API GL-5 API GL-4 or GL-5
    Weight (Reference)*1 Kg (lb) 41.2 (90.8) 42.8 (94.4)
    *1: Weight shows the figure with the oil fully filled.
    *2: TORSEN is TOYODA-KOKI-TORSEN’s registered trademark. NCF238U
  • hdfatboyhdfatboy Member Posts: 324
    This discussion is not about fairness. It was about information and sources. I appreciate you sharing the Toyota product brochure for the 2005 Sequoia as that is the first resource of any type that depicts the Sequoia in that year having a VF4AM transfer case. Obviously the other sources were incorrect.

    The Toyota info you shared does clear the matter up regarding the type of transfer case used in the pre-08 Sequoias. Curious that so many other sources would either be incorrect or would not have referenced that transfer case in the earlier model years.

    Based on your access to the Toyota site can you clarify which model years the Sequoia, LC, LX470 and the 4Runner each transitioned to a Torsen center LSD from an open center differential?
  • wwestwwest Member Posts: 10,706
    "..It would make quite a racket after it fails...."

    No, it wouldn't/doesn't. The spring pre-loaded clutch type, just as would a regular clutch in a stick shift, simply ceases to work once the friction surface has worn off. The VC type might "lock" in failure mode but since it is designed for "failsafe" operation that is rather doubtful.

    So a driver probably wouldn't notice the failure until the moment of need arises.
  • wwestwwest Member Posts: 10,706
    "..Once you are moving you wouldn't want ALSD (A-LSD) you would want TRAC on to keep stability.."

    Someone, please, correct this if you have information otherwise but I think I have read documentation indicating that A-LSD is a sub-mode of TRAC. Whereas TRAC's default, always on, mode will instantly apply braking to a slipping wheel and simultaneously dethrottle the engine, if you put the system in A-LSD mode it will allow a certain level of wheelspin/slip just as one might sometimes want to get unstuck.

    I think, also, A-LSD capability is only to be made available on RWD or R/AWD vehicles.

    For many years now owners have complained about this aspect of TRAC, no ability to use wheelspin, say for rocking the vehicle back and forth to get unstuck, out of a mudhole, and now Toyota is offering A-LSD as a possible solution. Previously the only solution was to somehow disable VSC/TRAC altogether.

    "..want TRAC on to keep stability."

    Methinks you meant to say VSC.
  • wwestwwest Member Posts: 10,706
    "That being said, it has disadvantages to a mechanical LSD in that slip has to occur before it goes into action...."

    Assuming a VC, Viscous Clutch, implemented LSD is considered "mechanical" your statement is wrong, a VC must experience a period of slippage before it will "tighten" the coupling coefficient.

    "A mechanical Torsen system.."

    Doesn't this add to the confusion? I have never considered the Torsen system to be in the LSD "realm", more of a torque control/distribution system rather than an LSD.
  • hdfatboyhdfatboy Member Posts: 324
    I was referring more to a Torsen type which would not operate seemlessly after failure.
  • hdfatboyhdfatboy Member Posts: 324
    Almost all references to the Torsen differential, including the manufacturer's refer to it as a LSD.

    You description of the viscous liquid diff is accurate and one of the reasons its not the best mechanical design for transfer of torque under severe conditions. It can be ineffective when operating in sand for example in transferring torque from the rear to the front of an AWD vehicle. It excels however at providing a very smooth torque transition when operating on slippery road surfaces.
  • wwestwwest Member Posts: 10,706
    "There is no reference anywhere I've searched that the Sequoia had a lockable mechanical center LSD prior to 2008."

    I thought the Sequoia ALWAYS had a lockable mechainical center diff'l for 4WD/4X4 mode...??

    And yes, while that was otherwise an "open" diff''l (or transfer case equivalent) I thought they used TRAC braking in AWD mode to effectively have a center LSD..?

    And isn't that basically the same system used quite effectively on the RX330/350, the HL and the Sienna AWD systems today, the VC version of those systems having been dropped prior to the '04 model year.
  • wwestwwest Member Posts: 10,706
    The way I read all of this is that Toyota has adopted the Torsen "C" center diff'l design so the engine torque to the front would/could be limited to not more that 40%. The "old" system, TRAC braking, could clearly result in 100% of the engine torque to the front driveline therefore quickly converting a reasonably beniegn handing rear torque biased AWD vehicle into a wildly uncontrollable, SCARY, FWD, F/AWD vehicle.
  • josephd05josephd05 Member Posts: 46
    Torsen center diff? Atrac on the front and rear diffs? I'm going from an 06 4runner which has an amazing 4wd system. I don't offroad much, but I want something thats capable in the rough weather. I knwo it wont match my runner, but I don't want to get stuck in the snow. Please advise gurus.
  • hdfatboyhdfatboy Member Posts: 324
    "I thought the Sequoia ALWAYS had a lockable mechainical center diff'l for 4WD/4X4 mode...?? "

    I thought I knew the answer until 2Toyotas shared information from the "Pay for" toyota website. While the Sequoia has always had a Lockable ctr differential, I thought the addition of the Torsen LSD (in place of an open diff) was new for 2008. He shared information describing a Torsen Ctr Diff in the 2005 model. Therefore I do not know when Toyota transitioned from an open diff to the Torsen LSD ctr diff. for the Sequoia.

    I was hopeful that 2Toyotas could look at his website to determine what model year the upgrade actually took place. (As well as when the upgrade to the Torsen occurred for the LC, LX470 and 4Runner.)

    Most external information sources suggest the Torsen was added to the drivetrain for these vehicles in 2008 with the 4Runner getting it earlier. These sources must be wrong based on his review of the Toyota site.
  • 2toyotas2toyotas Member Posts: 104
    The 4Runner was redesigned in 2003 and began using the VF4AM transfer on the V6 and the VF4BM on the V8. Both have the torsen center diff, with the V6 having a 2WD option.

    The Sequoia used the VF3AM transfer from it's introduction in 2001 until 2004. It has an open center diff. In 2005 the Sequoia started using the VF4AM transfer already in use on the V6 4Runner, which has the torsen. For 2008 the Sequoia is now using the JF3A transfer which also has the torsen.

    The Land Cruiser/LX470 used the HF2A transfer which has an open center diff. from 1998 until 2007. For 2008 the Land Cruiser/LX570 will use the JF2A which has a torsen center diff. One interesting thing is the Land Cruiser/LX used the HF2AV center diff until 1997 which had a Viscous center diff. They dropped it in 1998 for an open center diff.

    ATRAC began in the Land Cruiser/LX in 2000, and the 4Runner and Sequoia in 2001.

    The torsen center diff is definitely an improvement over an open center diff. I had an 03 Sequoia and then traded for an 05, and the big difference is on inclines, with the open diff ATRAC would brake up to 3 wheels at a time and 1 wheel would get power., it was not enough to get the Sequoia up inclines, you would need to lock the center diff. With the torsen both axles always get power, the front up to 53% and the rear up to 71%. ATRAC works side to side on both axles, while the torsen puts it front to back, so it climbs inclines with ease, without the need to lock the center diff.

    In my experience with this system, on snow and ice unlocked with the torsen working, ATRAC brakes spinning wheels and also cuts power when needed, and keeps the truck in full control. In sand or mud it is better to lock the center diff, this way power is split 50/50, and ATRAC only brakes the spinning wheel, but does not cut power, so it keeps you moving.
  • 2toyotas2toyotas Member Posts: 104
    Wwest you are right on. My point was if you are going down a highway at 50 mph you wouldn't want ALSD on you would want the default TRAC on. What I meant by TRAC for stability was ALSD does not really cut power, so if you were driving along in ALSD mode and hit ice on one rear tire your back end could slide out, but in default mode TRAC, it would also cut power to keep you straight, hence stability.
  • hdfatboyhdfatboy Member Posts: 324
    Very helpful summary. Thank you for the timeline info.

    Just to summarize...the Open to Torsen conversion for the center diff of these models took place in the following years:

    4Runner - 2003
    Sequoia - 2005
    LC/LX470 - 2008

    Is there any other Toyota made 4wd vehicle with a torsen ctr diff?

    You also shared that the Sequoia and LC/LX changed transfer cases in 2008. The Sequoia from VF4AM to a JF3A. The LC/LX from an HF2A to JF2A.

    Do you know what the primary difference is between the previous transfer case and the Sequoia's new JF3A? Also do you know what the difference is between the JF2A and the JF3A? Is the primary difference in the transfer cases between the LC/LX and the Sequoia the new "Hill Start Control" and the new "Crawl Control" which are in the LX/LC but not in the Sequoia?
  • nedzelnedzel Member Posts: 787
    The 2008 Highlander will do fine on trips to the mall in the snow. I always advise snow tires (which I have on my 2003 4WD 4Runner), since AWD/4WD systems help you go but don't help you stop. Whether or not you get stuck in the snow is all up to you -- don't drive in snow that is deeper than the ground clearance, use some caution, brake and steer gently and you'll be fine. I never got my 1987 Acura Integra stuck in the snow and it was far less capable than an AWD Highlander.

    The 2008 Highlander is significantly larger and heavier than the previous version, so don't expect to get significantly better mileage than your V6 4Runner.
  • wwestwwest Member Posts: 10,706
    NO torsen in the 4runner after 2003, apparently one year only...!

    Cannot find any documentation that the torsen was used after 2003 but lots of stuff indicating TRAC was used in its place. Same for the Lexus GX & LX series.

    Strange, very.

    Lot of component pictures/diagrams/breakouts of the VF4AM transfer across the years and models but only the 2003 4runner shows a torsen.
  • nedzelnedzel Member Posts: 787
    WWest: that is not correct. Go to: http://www.toyota.com/4runner/specs.html

    Look down at drivetrain: "Multi-Mode 4-wheel drive with Torsen® [1] limited-slip center differential with locking feature" for the V6 and "Full-time 4-wheel drive with Torsen® [1] limited-slip center differential with locking feature"

    The 4Runner drivetrain hasn't changed since 2003.
  • wwestwwest Member Posts: 10,706
    Yes, I know what all the advertising says, hardcopy and on the internet.

    Clearly, I may be wrong but the information at techinfo.toyota.com is pretty detailed, detailed well enough that a good mechanic could use it to overhaul the transfer system.

    The word "torsen" is not used beyond 2003 in any of the documentation and I have no idea why that would be unless it isn't used or there is some legality involved.

    Additionally if you read the document ion for traction control it appears that a torsen diff'l would be of no use since the TRAC system would quickly brake any wheel (and dethrottle the engine simultaneously) that exhibits spin or slip.

    As somewhat of a parallel, I bought a 2001 AWD RX300 because it had HID VSC/TRAC and a viscous clutch across the center diff'l to provide torque to the rear driveline if front slippage occurred.

    I quickly discovered that the VC was probably useless since the TRAC system activated at the first sign, seemingly the very instant, wheelspin developed.

    Apparently Lexus discovered the same thing as the VC was discontinued for the RX330 series as was announced in NCF, New Car Features for the new 2004 RX330.

    But guess what....??

    Lexus continued to advertise, hardcopy sales brochures, on the internet, and in various PR pieces, that the RX330 had a VC, Viscous Clutch when the shop/repair manual indicated otherwise.

    Lexus finally admitted, in writing (email), that the RX330 did not use a VC and apologized for the mis-information.

    And now here I am arguing with Lexus as to whether or not the new(er) RX350 uses the VC. The advertising says yes but the shop/repair manuals say not and the TRAC use indicates it might be useless even if it is installed.

    Sorta of like the issue of a torsen with TRAC in the 4runner.
  • wwestwwest Member Posts: 10,706
    Read the material, however sparse, on TC, Traction Control, on the provided link.

    If you have a torsen diff'l in the 4runner wouldn't you need to disable TC in order to put it to use...??
  • greengreen Member Posts: 15
    A torsen center diff, compared to an open center diff, enhances brake TC by multiplying the effect of a slipping, braked wheel by more than 1:1 across the axle diff to the other wheel. The amount depends on the bias ratio of the torsen.
  • wwestwwest Member Posts: 10,706
    Yes, but doesn't that seem counter-productive...??

    The front wheels are already slipping (abet at a rate limited by TC) an obvious indication of a slippery roadbed surface, and the Torsen will MULTIPLY the torque at the rear wheels (torque sustained via TC braking), or vice versa.

    I would think one would want LESS torque at the opposite wheels, not MORE.
  • wwestwwest Member Posts: 10,706
    The linked YouTube video gives certain evidence that the Highlander AWD system is quite clearly heavily biased to the front, as is probably the RX3X0 and the Sienna.

    But how...??

    http://youtube.com/watch?v=t09ExAUgtyE&feature=related
  • hdfatboyhdfatboy Member Posts: 324
    All 3 of these "4wd" vehicles (Highlander AWD, RX330 and Sienna AWD) are built off a variation of the Toyota Camry drivetrain which is FWD. All 3 of these vehicles have open center and rear differentials (unless someone has any new information on the '08's that they now have a LSD ctr diff)

    In reality these are FWD vehicles that transfer power when there is slippage using the brakes from the front wheels that are slipping to the rear one's that aren't. Generally these systems cannot transfer torque over a certain speed such as 35mph. Once you're over this speed, the brakes can no longer be applied to transfer torque to wheels that are not slipping and you essentially have a FWD vehicle.

    This type of system will generally use up brake pads more than a vehicle with a center LSD or Viscous liquid ctr diff. While Toyota refers to the system as "AWD", it would not meet the definition of AWD by most other manufacturer's that use this term such as Subaru, Audi, MB, Volvo or GM, however it is nice marketing even if its not a very effective 4wd drivetrain.

    Unless Toyota has added a Viscous Liquid center differential or a limted slip differential to these 3 vehicles, they would generally not meet the definition of AWD used by all other manufacturers of AWD vehicles.

    Since there's no operator controls it wouldn't meet the definition of a typical 4wd system either. Best way to think about this system is that its a FWD vehicle with traction control that transfers power to the rear wheels when the front wheels slip, but only at lower speeds and only a small amount of the available torque as shown in the video. Better than FWD alone but not nearly as good as a real AWD system or a 4wd system.
  • wwestwwest Member Posts: 10,706
    But I would think that TRAC could brake the front wheels enough to "force" enough torque to the rear to get the car in motion even with the obstacle blocking the rera wheels.

    Or is it just a matter of poor or inadequate TRAC design?
  • hdfatboyhdfatboy Member Posts: 324
    Using brakes to transfer torque is a very delicate balancing act. Braking too much will stop your momentum before the rear wheels have picked up the torque to keep the vehicle going. Therefore the software has its limitations and will only reduce the front wheel torque to a certain amount and only under a certain speed.

    The video shows the significant limitations of using braking to transfer torque across an open differential. As the video shows, a system such as Toyota's that is solely based on braking to transfer torque is a poor substitute for a mechanical LSD or viscous liquid CTR diff.. That's why the RX330/350 can't climb a slippery incline even when the front wheels slip and the rear has traction.

    If the vehicle was moving at speed, the system wouldn't even attempt to transfer torque in order to avoid causing an unstable driving situation, not to mention how much additional wear and tear would be place on the front brakes if the system attempted to use front wheel braking to transfer torque at higher speeds such as a highway ramp or even a high speed curve in a major highway.

    This type of system is simply Toyota's way of keeping drivetrain costs down and giving the marketing department a "claim" that most consumer's will never understand or see the difference with real AWD and 4wd drivetrains. Their approach allows for higher prices with lower costs and a better margin on their "AWD" vehicles. Smart buyers will know the difference and see this drivetrain as nothing more than a glorified traction system for limited road situations.

    Toyota loyalists will undoubtedly have a different perspective however the videos tell the real world story. Here's another example showing the difference between the Tundra's rear open diff with "electronic torque transfer via the brakes" vs the mechanical auto-locking rear differential in a Chevy pickup. A rear LSD would perform somewhere between the 2wd Tundra and the 2wd Chevy in this video. http://www.youtube.com/watch?v=Z8PpZF77tgk The video was filmed at the Eaton proving grounds which makes the Eaton auto-locking differential used in the 2wd Silverado pickup.
  • greengreen Member Posts: 15
    You may or may not want more depending on conditions, but the torsen-C center will require less frequent TC engagement and less brake pressure when it does engage, compared to an open center.
  • newdavidqnewdavidq Member Posts: 146
    I have an 07 4R V6 4x4 and want to say that the last two paragraphs of your post include absolutely the clearest and simplest description of my 4 wheel drive system I have read and that includes the owners manual!
    Thanks, DQ
  • 2toyotas2toyotas Member Posts: 104
    I did a little research on this whole topic. First the Tundra, if you go on Eaton's site they compare the GM's to a Ford F150 and a Dodge Ram. On the rollers, both the Ford and the Dodge slide back, with a mechanical limited slip rear differential, in 2WD and in 4WD. They can not make it up the rollers. The Tundra in ALSD mode did make it. They also state on their site that most trucks in 4WD can not get through the twisted ditch. It is funny that they only tested the Tundra in 2WD in ALSD mode. ALSD mode is mainly when you need some wheel spin in sand or loose conditions. They never showed it in 2WD normal mode, which is with TRAC on. Same thing on the ramp. TRAC would have slowed the spinning wheel and cut power to send power to the other wheel, I don't know if it would have worked, but it was never mentioned. One other thing is the Eaton locking rear diff. works in 2WD and 4WD in high and low range, but only up to 20 mph, after that it acts like an open diff. If it were me I would take the Tundra with a Traction system that always is on, and put it in 4WD when needed, you now have ATRAC working on the front and rear axles, and they didn't dare show that, because it would have ate up that whole test track!!

    As far as the Highlander, I would think it would do a better job than that, it looked like the TRAC system was disabled, but i can not prove that. I do agree, I would like to see the Viscous Coupling back in the center diff. My first Sequoia was an 03 which had a lockable open center diff. On steep inclines ATRAC would have to kick in to much and it would stop momentum. I would have to lock it, and it would be fine. I then bought an 05 which had the Torsen center diff, which corrected that problem.
  • lpackheiserlpackheiser Member Posts: 1
    HELP, HELP !! - I keep seeing "unlock center diff" - but how do you do that???? I am stuck in C Diff Lock, and will have to have my car towed - there does not seem to be any toggle/switch to turn it off. THANK YOU !
  • nedzelnedzel Member Posts: 787
    Have you read the owner's manual?

    In the 4Runner, the center diff is locked and unlocked by a push-button on the dash, low and to the left of the steering wheel. In the 2008 Sequoia, I believe it is to the right of the steering wheel. Look at this picture: http://www.autoblog.com/photos/2008-toyota-sequioa-limited-4x4/686920/

    See the button in the middle that has a little drawing that shows 4 wheels and an x in the middle? That locks and unlocks the center diff. You might have to put the car in neutral to unlock the center diff.
  • mike805mike805 Member Posts: 33
    Your article by Toyota on the Torsen ctr diff. is very good but requires a lot of study to understand. This would answer a lot of question if people took the time to understand this article. I'll have to give some thought to just how the gear angles provide the friction for limited slip and don't just wear out.
    I had thought mechanical limited slip was generally done with friction disks as was the case in my '60s GTO and Corvette. In that case I'm not sure but what using the brakes isn't a better solution. It is sure easier to replace brake pads and in those cases the limited slip did wear out.
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