Last post on Apr 28, 2012 at 12:48 PM
You are in the Toyota Sequoia
What is this discussion about?
Toyota Sequoia, Toyota Highlander, Toyota 4Runner, Toyota Land Cruiser, Toyota RAV4, Toyota Tacoma, Truck, SUV
#2127 of 2487 Re: RAV4 .vs. Subaru AWD [nedzel]
Jan 15, 2008 (12:57 pm)
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.
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).
Jan 15, 2008 (3:20 pm)
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.
#2129 of 2487 Re: e [trebor129]
Jan 15, 2008 (5:30 pm)
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).
#2130 of 2487 Re: e [trebor129]
Jan 15, 2008 (6:06 pm)
"....*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?
Electronic via brakes?
Not talking LOCKING diff'l here, only LIMITED slip.
#2131 of 2487 Re: e [hdfatboy]
Jan 15, 2008 (6:09 pm)
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..??
#2132 of 2487 Re: RAV4 .vs. Subaru AWD [hdfatboy]
Jan 15, 2008 (6:38 pm)
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.
Jan 15, 2008 (8:36 pm)
"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.
Jan 15, 2008 (8:39 pm)
LSD means 'limited' slip. It does not stop all slip. So yes, electronic braking system is a benefit because it can stop all slip.
Jan 15, 2008 (8:44 pm)
"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.
#2136 of 2487 Re: d [trebor129]
Jan 15, 2008 (8:49 pm)
"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.