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SequoiaGeneral discussion forum for the second generation 2008 and later Toyota Sequoia.
This is a discussion thread titled "Atrac/trac", within the Sequoia forum, part of the SUV Forums category.
The difference between A-Trac and TRAC is that A-Trac is for 4WD and TRAC is for 2WD.
Here's a definition of each that I found on the Toyota Canada site:
A-TRAC
Benefit: Helps prevent drive wheel spin on slippery surfaces and in off-road. This system applies brake fluid pressure to the slipping wheel, distributing the drive force that would have been lost, to the remaining wheels. At the same time, engine power is reduced through the Electronic Throttle Control System (ETCS-i). This system applies to all 4 wheels and eliminates the need for front, centre or rear differential control (Locking or Limited Slip) in most cases. A-TRAC functions as 4-Wheel Traction Control.
TRAC
Benefit: Helps prevent drive wheel spin on slippery surfaces. When sensors detect that one of the driving wheels is about to spin, TRAC applies its particular brake and - if necessary - also reduces engine output until the spinning stops and the wheel regains traction. By applying the brake, the torque is sent to the opposite wheel, thus acting like LSD.
In Canada, the 2008 Sequoia is NOT available in 2WD so the brochure only talks about A-TRAC. There's no mention of TRAC, so I would assume that a vehicle would have one or the other, but not both.
I'm going in to take another look at the Platinum tomorrow so I'll check to see if there's any way to disable it (but I kinda doubt it).
Edit:
I just re-read the other thread you started and saw that eddeeeee had answered your question already. It's good that it can be disabled because it gives more control to the driver. My old Sequoia could disable the VSC while off-roading, but not the traction control.
One more thing, even though Toyota says that A-TRAC "eliminates the need for front, centre or rear differential control (Locking or Limited Slip)" my brochure does say that the Sequoia has a Torsen limited-slip differential.
One more thing, even though Toyota says that A-TRAC "eliminates the need for front, centre or rear differential control (Locking or Limited Slip)" my brochure does say that the Sequoia has a Torsen limited-slip differential.
The center torsen LSD on the 08 Sequoia, LC and LX570 were an absolute necessity. There's no way that a brake-enduced approach to transferring torque would work effectively with an engine producing over 400ft/lbs of torque. The A-Trac system is nothing more than software that optimizes the ABS system to focus on torque transfer during slippage instead of just stopping power.
Without the mechnical Torsen center LSD, the Sequoia/LC/LX would be chewing through brakes faster than a 13 yr old in front of a bowl of cheerios in an attempt to manage the 5.7's torque output to avoid wheel slippage. Now if only Toyota would apply the logic they used to incorporate the mechanical LS center differential and add a mech LSD to the rear, we could really maximize the 5.7's torque capabilities to the fullest.
So far, I haven't noticed much of a chatter from the operation, but it hasn't kicked in much. My 06 Sequoia kicked in many times on a drive ( we have a lot of gravel on the roads in Denver ) and almost everytime pulling into my neighborhood where we have a drainage pan that I drive through. The new design is much less intrusive, much less sensitive, and while not silent, it is not really noticeable.
Wouldn't the chattering simply be a characteristic of the way that ABS works? I know when I activate ABS on different vehicles, each has a slightly different sound/feel--but that vibration/noise is normal.
I do agree though that traction control/VSC on the 1st gen Sequoia was too intrusive.
The rear diff on the Sequioa has a very 'weak' LSD feature. The diff is an all new 10 incher, and one of the side gears has a conical spring that applies pressure and a bit of friction between that side gear and the case... it gives a slight LSD action. More than anything it probably smooths the TRAC/ATRAC functioning.
Some of the older watercooled VW's had this feature(?) and folks would shim the spring to get a little more action out of it.
The rear diff on the Sequioa has a very 'weak' LSD feature. The diff is an all new 10 incher, and one of the side gears has a conical spring that applies pressure and a bit of friction between that side gear and the case... it gives a slight LSD action. More than anything it probably smooths the TRAC/ATRAC functioning.
Some of the older watercooled VW's had this feature(?) and folks would shim the spring to get a little more action out of it.
The rear differential of the 08 Sequoia, LX570, Land Cruiser, 4Runner, Tundra, in fact all 2008 Toyota rear differentials are mechanically "open differentials". There is no mechanical design in these differentials that limits the slip in the rear from left to right. The Atrac and Trac systems do transfer torque by limiting the slip at the wheels but use the ABS braking system to stop (slow) one wheel from slipping using the brake in order to transfer torque through the open diff to the non-slipping wheel. Inherent design limitation is that this approach is not designed to limit slip above 35 mphs as it would cause unnecessary wear and tear on the brakes. Both Atrac and Trac are deactivated by the ABS system above 35 mphs.
Unfortunately Toyota continues to market their vehicles as having rear LSDs (which is really Atrac in 4wd and Trac in 2wd). Quite misleading to most consumers as almost all manufacturers use the term "rear LSD" to mean their vehicle has a rear "mechanical" LSD, not merely electronic slippage control.
....There is no mechanical design in these differentials that limits the slip in the rear from left to right...
...Really, there is in the 10"Sequoia diff, I'm not making this stuff up, but it would be fun . It is an open diff with spring pushing between one side gear and the housing. It is no where near a true mechanical LSD. Toyota calls it a pretorque mechanism or something like that.
...Really, there is in the 10"Sequoia diff, I'm not making this stuff up, but it would be fun . It is an open diff with spring pushing between one side gear and the housing. It is no where near a true mechanical LSD. Toyota calls it a pretorque mechanism or something like that.
Without clutch plates or a viscous liquid design, a rear differential would not meet the typical definition of a mechanical LSD as the term has been used by vehicle manufacturers for over 50 years. I would be interested in any link that has more information on the design of the 08 Sequoia and Tundra rear diff that describes it as anything other than an open diff.
Please note I said "...very 'weak' LSD feature..." and "...slight LSD action..." I don't really consider it a LSD, but it does provide a smidge bit of LSD type workings through mechanical means. Low power on slippery surfaces are the intended place of gain. I'm not looking to argue about it... it's in there and it creates slight torque transfer. The new Lexus IS-F also has one in the rear differential. The Tundra, Land Cruiser, and LX570 do not have it. The only place I have seen any info about it is under the NCF (new car features) on the Toyota TIS webpage.
Please note I said "...very 'weak' LSD feature..." and "...slight LSD action..." I don't really consider it a LSD, but it does provide a smidge bit of LSD type workings through mechanical means. Low power on slippery surfaces are the intended place of gain. I'm not looking to argue about it... it's in there and it creates slight torque transfer. The new Lexus IS-F also has one in the rear differential. The Tundra, Land Cruiser, and LX570 do not have it. The only place I have seen any info about it is under the NCF (new car features) on the Toyota TIS webpage.
Is there any other info on the 08 Sequoia rear diff. on the TIS webpage? There is nothing available on the internet beyond the marketing claim of A-LSD and it being an open diif. I'd be interested in reading about how they are generating slight or very weak friction across the rear transaxles upon slippage (other than the application of brakes through A-LSD/A-Trac,Trac).
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Atrac/trac
. It is an open diff with spring pushing between one side gear and the housing. It is no where near a true mechanical LSD. Toyota calls it a pretorque mechanism or something like that.
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