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Toyota 4WD systems explained

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  • Hi: Just purchased a new Tacoma and while driving home the 4 Wheel Indicator light (the icon in the dash that looks like a set of 4 wheels with the axle/transaxle) kept flashing on and off. The 2/4 wheel drive selector knob was pointing to 2H...so it should have been in 2 wheel drive. I stopped, put the vehichle in park, set the knob to 4H and then (pushed) and put it in 4L and then back to 2H. Still had the flashing light. It also "felt" like it was in 4 wheel drive...but am not 100% sure it was.

    Any way to know whether it is in 4 Wheel drive, other than depending on that "4 Wheel light" indicator on the dash?

    I plan to take it back to Dealer, but just wanted to get some insight from unbiased folks.

    Thanks, Zingaro_Mom!
  • wwestwwest Posts: 10,706
    Sorta just guessing but the flashing icon generally means the drive system is in transition, in the process of shifting from 4WD to 2Wd or vice versa. Sounds as if yours is stuck in between.
  • hdfatboyhdfatboy Posts: 324
    "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."

    I think the Toyota warranty is actually a pretty good deal if you have any intention of keeping the vehicle for 100,000miles. I think it is almost a given that something is going to break on the 08 Sequoia between the 3rd year and the 7th year of ownership or between 36,000miles and 100,000miles. Even more likely given its a new model with a new engine, new rear suspension design, new electric seat design, new 6sp transmission design, new 4wd system design, etc.

    I am equally sure that whatever breaks during that period is likely to cost significantly more than $1000. Combined with the fact that unlimited towing and a rental car is included in the Platinum warranty, it seems a pretty reasonable bet to purchase a 7yr/100,000mile/$0 deductible from Toyota, particularly if you can purchase it for under $1000.
  • hdfatboyhdfatboy Posts: 324
    It really depends which Toyota 4wd system you are referring to. 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). I believe there is still a significant disadvantage that remains in Toyota's A-LSD system.... it does not function above 35mph. This limitation means that for all of these Toyota vehicles with the new 4wd system, when operating above 35 mph, they really only have traction to one wheel on the front end and one on the rear distributed through the mechanical center differential (the rear differential is still open on the new 4wd system). This can make a difference on wet highway ramps and other higher speed situations (above 35mph) where traction at all 4 corners is desirable.

    The power is distributed through the new Torsen Center Differential with a range of 30/70 upto 50/50 when operating in full-time 4wd. The other downside to Toyota's A-LSD is that because it is based on using the brakes to distribute torque when there's slippage (below 35mph), it can have a tendency to wear out brake pads sooner than a system that doesn't use brakes to distribute torque (ie, mechanical LSD or lockable LSD). I don't know how much additional wear there is but it must be something vs a non-brake method for distributing torque during slippage.

    Toyota's new full-time 4wd design is better (for on-road use) than the old system which had 3 open differentials, but its still not as good as AWD systems used by Audi, Subaru, Dodge, GMC and Cadillac that use a LSD for the center and the rear of their FT 4wd drivetrains.
  • wwestwwest Posts: 10,706
    "..when operating above 35MPH...."

    In normal, non-adverse roadbed, conditions none of these engine/transaxle combinations will produce enough torque to induce wheelspin/slip above 35MPH, so above that speed the number of driven wheels is generally not of matter.

    If you have reached 35 MPH and the roadbed is slippery enough that the engine will induce wheelspin/slip and you force it to do so you simply do not belong on the same roads as others with more common sense.

    With A-LSD I suspect the manufacturers have an expectation that over time the drivers will adapt to "learned" road conditions and thereby do their own "feathering" of the throttle to avoid wheelspin/slip. That should avoid most uses of the brakes to implement the A-LSD system.

    The TC, Traction Control, system in my '92 LS400 works very well as a warning, heads up indication, of roadbed conditions for which I may have been unaware, was unaware, but once I get that warning I typically turn it off and drive a bit more cautiously, as conditions warrant.
  • hdfatboyhdfatboy Posts: 324
    "In normal, non-adverse roadbed, conditions none of these engine/transaxle combinations will produce enough torque to induce wheelspin/slip above 35MPH, so above that speed the number of driven wheels is generally not of matter.

    If you have reached 35 MPH and the roadbed is slippery enough that the engine will induce wheelspin/slip and you force it to do so you simply do not belong on the same roads as others with more common sense."

    Your view may be reasonable however there have been enough circumstances where I was on a sloping ramp in snowy or wet conditions that I was glad I had a true AWD/FT 4wd system that incorporated a mechanical LSD in both the center and rear differentials. Obviously Toyota engineers felt it offered enough of a benefit to warrant their change over to a mechanical center differential on their newest high-end 4wd models. I just wish they had done the same on the rear differential for the same reason they elected to incorporate it into the center differential.

    I would think MB, Audi, Subaru, GMC, Dodge, Cadillac, BMW, Chevy, Land Rover, Porsche designed their AWD/FT 4WD systems with a mechanical LSD in both the center and rear of their drivetrains for a good reason. IMHO that reason being that it delivers a more sure-footed driving experience without the speed limitations and brake wearing downsides of the Toyota electronic approach.
  • wwestwwest Posts: 10,706
    Are you really sure that all those you named, AWD/FT 4WD systems, truly have a rear mechanical LSD..?? When the primary drive is not at the front a rear mechanical LSD vs a brake implemented LSD might make little difference in actuallity, all conditions.
  • hdfatboyhdfatboy Posts: 324
    wwest,

    Here's an article that might be of interest on the differences between AWD & 4WD.
    http://www.omninerd.com/blogs/4WD_vs_AWD_and_the_Fallacy_of_Snow_Traction

    2008 Audi S4 Quattro http://consumerguideauto.howstuffworks.com/2008-audi-a4-5.htm
    "4.2-liter 340-horsepower V8 engine, 6-speed manual or 6-speed automatic transmission w/manual-shift capability, all-wheel drive, front and rear limited-slip differentials".

    2008 Chevy Tahoe LTZ 4WD http://autos.yahoo.com/chevrolet_tahoe_ltz_4wd-review_article/?source=nctd
    "a limited-slip rear differential"

    2008 Subaru Baja http://www.allautoreviews.com/auto_reviews/subaru/suburu-baja.htm
    "5-speed manual transmission full time 4WD viscous center differential center locking differential rear limited slip differential"

    2008 GMC Denali http://www.motortrend.com/cars/2008/gmc/yukon/denali_sport_utility/553/specifica- - - tions/
    "Rear limited slip differential "

    2008 Cadillac Escalade Same as Denali

    2008 Dodge Dakota 4WD http://www.dessources.com/en/newcars/perfectcar/index.spy?carid=1081500811&ORIGI- - - N=0&DEALERCODE=514DESSOURCESDODGE&lng=en
    "Limited-slip rear differential"

    2008 Mitsubishi Lancer Ralliart http://www.autoblog.com/2008/01/13/detroit-2008-2009-mitsubishi-lancer-ralliart-- - - were-sold/ "4wd Lancer Ralliart is also equipped with front helical limited slip differential and a rear differential mechanical limited slip differential"

    2008 BMW All M series and Z series vehicles have mechanical LSD in the rear. It is unclear what type of differential is used in the rear of the X series. They do use a mechanical LSD for the center but I was unable to find info on the rear. http://www.motortrend.com/cars/2008/bmw/x5/specifications/

    2008 Land Rover LR3 http://www.automobilemag.com/am/99/2008/land_rover/lr3/hse_sport_utility/877/pac- - - kages_options.html
    "Heavy Duty Package - $625 Rear limited slip differential"

    2008 Porsche Cayenne http://www.allautoreviews.com/auto_reviews/porsche/porshe-cayenne.htm
    "6-speed shiftable automatic transmission descent control four wheel drive full time 4WD hi-lo gear selection front, center and rear locking differential"

    2008 MB 4matic http://www.edmunds.com/mercedesbenz/sclass/2008/review.html
    This is a new system for 2008 and appears to have a mechanical LSD for the center and electronically locking front and rear diffs. The S63 does have a rear LSD. "a performance package for the S63 provides a limited-slip rear differential"
  • wwestwwest Posts: 10,706
    "..provides a limited slip rear differential"

    Uisng a viscous clutch, a spring pre-load clutch set, or....

    the brakes...??
  • 2toyotas2toyotas Posts: 104
    You should really know more about Toyotas 4WD Systems before commenting. First, the Torsen Center Differential has been in the 4Runner since 2003, and in the Sequoia since 2005. Second ALSD only operates in 2WD, and is engaged by pressing a button. All other times TRAC is on, and works at any speed. TRAC will brake the slipping wheel and cut engine power for stability, which is what you would want above 35 mph. ALSD will brake the slipping wheel to give equal power to each wheel. When these vehicles are in 4WD ATRAC operates at all speeds on both axles. When the center diff is unlocked the Torsen will split power 40 front and 60 rear in normal driving, and up to 53% of power can go to the front, and 71% can go to the rear. ATRAC will brake spinning wheels and cut engine power for stability. When the Center Diff is locked power is split 50/50 and ATRAC will just brake spinning wheels, it does not cut engine power. When LOW range is engaged ATRAC does not cut engine power, and brakes wheels to keep driveability, instead of stability. This is on both front and rear axles, and is said to be equal to a vehicle with the center and rear diffs locked. A Sequoia, 4Runner, or Land Cruiser/LX570 will go farther without getting stuck than any Cadillac,Denali,Audi, or Subaru.
  • To recap, 2toyotas, how does the RAV4s' 4WD system work?
    Is it similar to the 4runner?
  • nedzelnedzel 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 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 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 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 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 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 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 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 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.
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