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SUVs Toyota Sequoia Toyota 4WD systems explained
2400 messages, Last post on Nov 22, 2009 at 10:30 AM
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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.
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Replying to: trebor129 (Jan 15, 2008 2:20 pm) 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).
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Replying to: trebor129 (Jan 15, 2008 2:20 pm) 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.
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Replying to: hdfatboy (Jan 15, 2008 4:30 pm)
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Replying to: hdfatboy (Jan 15, 2008 10:45 am) 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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Replying to: wwest (Jan 15, 2008 5:06 pm) 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. |
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LSD means 'limited' slip. It does not stop all slip. So yes, electronic braking system is a benefit because it can stop all slip.
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Replying to: wwest (Jan 15, 2008 5:09 pm) 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.
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Replying to: trebor129 (Jan 15, 2008 7:39 pm) 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.
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Replying to: 2toyotas (Jan 15, 2008 5:38 pm) 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- /
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