Ask the Car People.SM


Toyota 4WD systems explained

2487 messages,  Last post on Apr 28, 2012 at 12:48 PM

You are in the Toyota Sequoia Forum.

What is this discussion about? Toyota Sequoia, Toyota Highlander, Toyota 4Runner, Toyota Land Cruiser, Toyota RAV4, Toyota Tacoma, Truck, SUV

Messages Page 214 of 250

#2126 of 2487 Re: RAV4 .vs. Subaru AWD [2toyotas] by hdfatboy

Jan 15, 2008 (11:45 am)

Replying to: 2toyotas (Jan 14, 2008 10:59 pm)
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

#2127 of 2487 Re: RAV4 .vs. Subaru AWD [nedzel] by hdfatboy

Jan 15, 2008 (12:57 pm)

Replying to: nedzel (Jan 15, 2008 9:27 am)
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).

#2128 of 2487 e by trebor129

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] by hdfatboy

Jan 15, 2008 (5:30 pm)

Replying to: trebor129 (Jan 15, 2008 3:20 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] by wwest

Jan 15, 2008 (6:06 pm)

Replying to: trebor129 (Jan 15, 2008 3:20 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?
 
Viscous fluid?
 
Torsen?
 
Electronic via brakes?
 
Not talking LOCKING diff'l here, only LIMITED slip.

#2131 of 2487 Re: e [hdfatboy] by wwest

Jan 15, 2008 (6:09 pm)

Replying to: hdfatboy (Jan 15, 2008 5:30 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] by 2toyotas

Jan 15, 2008 (6:38 pm)

Replying to: hdfatboy (Jan 15, 2008 11:45 am)
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.

#2133 of 2487 Re: e [wwest] by hdfatboy

Jan 15, 2008 (8:36 pm)

Replying to: wwest (Jan 15, 2008 6:06 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.

#2134 of 2487 d by trebor129

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.

#2135 of 2487 Re: e [wwest] by hdfatboy

Jan 15, 2008 (8:44 pm)

Replying to: wwest (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..??"
 
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.

Messages Page 214 of 250

To POST a message, please Sign In.

Advertisement

Browse by Category

Browse by Vehicle
   View All Vehicles

Browse by Board
Browse by Topic
View All Topics

Edmunds Community

Advertisement