A-TRAC/TRAC/AUTO LSD Explained (Easy to understand, I hope!)

Chris4x4, I think your observation is correct and on the money.

jandrews, that might be true if you have a mechanical breakdown. The system seems to just not allow one to get stuck, it's that good.... although tires and air pressure will make a big difference along with driver skill!

kodiakisland, I would save your money for other equipment that your truck doesn't have... since it has 'limited slip' already. A rear locker would be the first choice if you didn't get the Off Road TRD.

 

Will adding a locker affect how the auto LSD and ATRAC/TRAC system works?

 

You don't have ATRAC unless you have an '09+ TRD Offroad 4x4

 

I was not asking what I have.

 

My bad

Let me rephrase that then , adding a locker to your truck won't affect your ATRAC because you don't have ATRAC

 

In H4 with TRAC on, do you get LSD in the front diff as well as the rear? Also, if you do the mod that gives TRAC in L4, does it void the warranty?

 

That still doesn't answer my question. My truck may not have it but my FJ does.

Let me ask again. Will adding a locker affect how any of the toyota auto LSD, ATRAC, or TRAC work?

 

What I was trying to ask is, in H4, does TRAC act on both front and rear diffs with a limited slip action or does TRAC only provide limited slip to the rear?

 

That's what I'd like to know. I've heard that TRAC would interfere with a Detroit Trutrac lsd because the braking action on a slipping wheel would prevent the Trutrac from sending torque to the other wheel, making it worthless unless you turn off TRAC in H4 mode. In L4 with open diffs, that wouldn't be a problem.

 

Curious who came up with that? Truetrac is gear driven LSD and when one wheel is completely i nthe air it will not send power to other wheel. So its common for people to apply brakes to force Truetrac to engage wheel on the ground.
ATRAC does the same thing except it does that better by applying brake to "ONLY" wheel in the air (aka slipping)
I dotn think you going have problems with truetrac and ATRAC when offroading.

 

I'm talking about TRAC applying the brake on the slipping wheel, not the driver, and with both wheels of that axle on the ground. Yes, Trutrac is gear driven, and when both wheels are on the ground and one is slipping, Trutrac transfers torque to the other wheel, however, if that diff has TRAC, it will use the brake on the slipping wheel to transfer torque to the other wheel, and so prevent Trutrac from actuating, or so the story goes.

 

Hi Kodiak, perhaps it would be helpful if you read the first page(s) of this thread, now many years old... However, I don't mind repeating myself, only that it seems to irritate the others here... LOL!

TRAC (in H4) works the FRONT and REAR tires, and will limit slip so power can be utilized by the tire(s) with more traction. I have discovered TRAC in H4 gives the truck more traction than when in L4 with no traction control (A-TRAC or Rear Locker) on.

The mod (4-low-trac mod) for non A-TRAC equipped Tacomas fools the system into thinking it is still in high range, when you are in L4, giving you TRAC in low range... It has been reported to be a night and day difference in off roading by those who have performed it.

The A-TRAC (and TRAC to a lesser degree) uses wheel spin sensors and the ABS brake system to stop wheel spin when there are other tires with traction. The rotation speed of a non-traction tire is matched to the other tire on that axle, so they both rotate the same with equal power... as does a locker.

The difference between A-TRAC and a locker is that it will not keep the tires locked together when there is no need for it, so steering is not affected. It comes with the 4WD Off Road Tacoma package and I have used it many a times at slow, crawling speed... well every time I am in low range... and who drives anything but slow while the transfer case is in L4?

On the other side of the A-TRAC comparison, is that the system makes some odd noises when it is working, like when you have wheel spin. Because it doesn't stay in a locked mode there is some more wheel spin than if you have lockers front and rear. A locked rig will climb a grade quicker and quieter, without excess spin, but an A-TRAC rig will get you to the same place, with a bit of spin as it rechecks if it is needed and a bit of noise... and it is included with the truck price.

The A-TRAC gets me to ALL the same places my older Tacomas with the rear locker used to get me to, and perhaps better with no fear of getting stuck anymore. The truck still has a rear locker, but I have only activated it when pulling other trucks up mountains or experimenting with how the various drive modes work. I did like using the rear locker and A-TRAC together in snow, since the locker being on allows wheel spin as the A-TRAC is disabled (on the front tires) at any speed above 3 MPH.

I hope this helps, and sorry but I cannot answer the warranty question about performing the mod, as I don't need it.

 

Maybe!??

In H4 we 2009-2011 have 'TRAC', but it is without engine regulation (same as AUTO LSD is in H2). We also can hold down the button in H4 for VSC OFF for no traction control or stability control.

The 2012+ might have two traction on choices, as well as VSC OFF, and that is TRAC (has engine regulation, like in 2WD) and now AUTO LSD in H4 (was called TRAC before)... only Toyota calls it 'TRAC OFF' (instead of AUTO LSD).

So, (maybe) there is an extra choice for the 2012+ Tacomas...

In H4:
TRAC (traction control with engine regulation)
TRAC OFF (traction control without regulation)*
VSC OFF (no traction control or stability control)

* this was called 'TRAC' until 2012, and the same function as AUTO LSD in H2, but on all 4.

 

David K, thank you for dumbing this down. I read the manual and it was Greek to me. Here I feel like I learned something. Mostly not to mess up my Tacoma.

 

2012 I thinkums it's all the same as 2009-2011. I'm not including A-TRAC since I don't have it, but I think it is the same for 2012-2013. The owners manual states this - and I've verified by actual use:

2WD (either 2WD models or 4WD models) default mode: VSC on, TRAC on.
2WD (either 2WD models or 4WD models) briefly pressing the "VSC OFF" switch: VSC off, Auto-LSD on.
2WD (either 2WD models or 4WD models) HOLDING "VSC OFF" switch down: VSC off, TRAC off, Auto-LSD off. Open differential.
4HI default mode: VSC on and TRAC on.
4HI briefly pressing "VSC OFF" switch: VSC on, TRAC off.
4HI holding "VSC OFF" switch down: VSC off, TRAC off. Open differentials.
4LO default mode: VSC off, TRAC off.

Does that differ at all for the 2012? Seems the same to me.

 

Yes, as our (2009-2011) trucks do not have a quick touch mode in H4 (nothing changes, comes on or goes off).

The quick touch only works in 2WD, and it activates AUTO LSD. TRAC in H4 (2009-2011) hasn't any engine regulation like it does in H2.

So, the $20,000 question: Is TRAC OFF in H4 the same as the TRAC in H4 used to be, which was the same as AUTO LSD in H2, but on all 4.

 

No worries Dave, I want to clear it up rather than dumb it down. If I only had a 2012 to play with a little while...

IMO: Toyota should have used the term AUTO LSD in both H2 and H4. Instead they used the word TRAC but it was different systems in H2 and H4!

Now, I think they added a third term to mean the same, and that is 'TRAC OFF'??? In 2WD they do say TRAC OFF MODE is AUTO LSD ON MODE. So why not call it AUTO LSD in H4 like they do in H2???

2WD: TRAC (regulated limited slip), AUTO LSD (unregulated limited slip), VSC OFF (no limited slip)

4WD-HI (2012+): TRAC (regulated limited slip), TRAC OFF (unregulated limited slip), VSC OFF (no limited slip).

 

Hmmm, yes, I see, I see (not really, but maybe I'll figure it all out eventually). More likely YOU'LL figure it out. Perhaps the difference is on this 2012 in 4HI, VSC is still enabled (but TRAC off) with the one-touch???? You'll have to tell me cause I'm having a hard time sorting through all this.

Maybe an explanation of my terminology will help you figure it out. I'm going by the instrument panel lights. On this 2012 SR5 there's three of them that light up to indicate what is going on - "Auto-LSD", "TRAC OFF", and "squiggly symbol OFF".

SO - when I post this breakdown below I'm going by what panel lights are either lit, or not lit. Here's an explanation of my terminology:

VSC on - "squiggly OFF" is not lit.
VSC off - "squiggly OFF" is lit.
TRAC on - "TRAC OFF" is not lit.
TRAC off - "TRAC OFF" is lit.
Auto-LSD on - "Auto-LSD" is lit.
Open differential(s) - Both "squiggly OFF" and "VSC OFF" are lit, "Auto-LSD" unlit.

2WD (either 2WD models or 4WD models) default mode: VSC on, TRAC on.
2WD (either 2WD models or 4WD models) briefly pressing the "VSC OFF" switch: VSC off, Auto-LSD on.
2WD (either 2WD models or 4WD models) HOLDING "VSC OFF" switch down: VSC off, TRAC off, Auto-LSD off. Open differential.
4HI default mode: VSC on and TRAC on.
4HI briefly pressing "VSC OFF" switch: VSC on, TRAC off.
4HI holding "VSC OFF" switch down: VSC off, TRAC off. Open differentials.
4LO default mode: VSC off, TRAC off.

So - perhaps the one difference is VSC on in 4HI with TRAC off. Or, as you said no difference really just a change in terminology???

I can say from experience in snow that in 4HI default mode the truck acts like both differentials are "locked" or at least semi-locked. I can back up my steep and canted concrete driveway in deep snow with these Dunlops and both the front and rear ends will move sideways, indicating all four wheels have some gription.

I haven't one-touched the "VSC OFF" switch in 4HI to see the difference. Too bad, that might have helped you figure it out. Nor have I held down the "VSC OFF" switch in 4HI. Too bad, now I'm curious how the truck will behave doing so. It never occurred to me to use the switch since the truck did fine in snow and some mild mud even with the Dunlops.

 

Funny Anthony! LOL

monkeyface: There is no TRAC OFF light in the pre-2012 Tacoma. There is no quick push of the VSC button in H4 (nothing happens).

In the 2009-2011 Tacoma in H4 we only have TWO modes:
TRAC (but without the engine regulation, so it is like AUTO LSD)
VSC OFF (both TRAC and VSC are off, but there is no 'TRAC OFF' light, only the VSC OFF light.)

So, the million dollar question is what is happening with the 2012+ Tacomas in 'TRAC OFF' mode vs. the normal (TRAC ON) mode?

I am thinking it is just another name for AUTO LSD but on 4 wheels, ie. strong limited slip without engine output regulation. It was called TRAC on 2009-2011 4WDs, but not the same as TRAC is in 2WD (where engine output is regulated)?

 

Well I am sure that on my 2012, the default 4wd mode has Trac AND engine regulation. I was driving slow across a field not too long ago and hit an unexpected soft spot. Switched to 4H and proceeded to spin my way out then the engine kinda shut down on me. I let off and gassed it again it spun for a few secs then the engine cut out again. I started to worry I might be stuck at this point so I didn't think to hit any buttons or anything. So I let off and gassed it once more and then my truck started moving more and the engine did NOT cut out. It seemed like the truck detects forward movement and bypassed the regulator, cause when the truck was barely inching forward it cut the power really quick.