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

Christian & David,

Thanks for picking up my spirits guys...I will try to find the thread in which David references on the yellow wire mod (4-Lo Trac Mod) and read some more about it to learn how too. Again, thank you both, it's people like you that share your professional knowledge that makes us all very proud and respect this site.

Gunny

 

You are welcome... and thank you for the nice remarks! Here is the link to the 4low-trac Mod thread (by Isthatahemi): http://www.tacomaworld.com/forum/technical-chat/51946-4low-trac.html

 

Just did some testing on steep (45 degree) slippery dirt paths and found some interesting things about how the TRAC, ATRAC, Locker, and Hill Decent systems work.

Open everything and 2WD I would immedicately get sutck on hills. Limited slip 2WD allowed me to get ON the hill but then it would spin, no matter how hard the LSD would work.

If I let off the brake the Hill Control would pulse my brakes as I went down backwards, stopping me for a brief second then letting go. It did this a few times then my vehicle engine would die and Id roll backward out of control while in drive and with no power. If I did it (go downhill) going forward it would pulse the brakes at about 7mph and then slow me down and pulse each time I started to accelerate and I could go down a mountain and never go too fast but it was jerky as hell, not smooth at all, and quite loud.

4HI and TRAC. This would let me spin and if I maintained throttle it would slowly start pulsing harder on the brakes to transfer more torque. When it first kicked in I would just keep spinning and then gradually it would start pulling me forward more and more till I regain momentum.

With 4LO and ATRAC it just grabs all at once and if you dont move immediately it just is not going to work. It was steep enough that on certain ledges and similar that the initial spin from ATRAC before it engages would kill my momentum and casue me to slip back and I either immediately would move up and over when it kicked in or it would not work. It was not like TRAC where it would transfer more and more torque till I got over the obstacle and it worked MUCH faster and got me over more difficult obstacles.

With the locker and no ATRAC it was always smooth. If I hit a ledge with my front tires and one tire was not getting traction up front, I could be stopped and the rears just spin and Id go straight from movement to no movement, spinning in place. With ATRAC plus locker the rears would never slip and hold me to the ledge, then ATRAC would kick in up front and id move over the ledge right away, or it would just not work at all. It was real obvious if you were going to make progress. If you hear lots of brake pulsing and you are slipping.... you wont be getting past that obstacle and need to try again. Not like TRAC where you just hold the accelerator and wait a couple seconds for the computer to decide it needs to transmit more power to that one brake on each pulse to get you moving. Often, TRAC requires A LONG CONTINUOUS THROTTLE APPLICATION. Otherwise you wont get enough traction to the other tire to move forward. Youd sit spinning, hold throttle, feel pulsing and no forward movement, then feel each pulse cause a larger surge forward (with a slight falling back between pulses) till you finally got enough forward momentum to not be rolling back between pulses and youd keep moving forward.

Its really interesting and enlightening to feel these work over several seconds straight as they normally pulse for less than a second under normal offroad conditions... its got to be 45 degrees or steeper to REALLY see how they work. TRAC seems to ramp up over time tif you keep slipping. ATRAC grabs all at once and seems to slowly "unpulse" the brakes for lack of a better description. It feels like default is the front brakes are locked. If the default of TRAC is spining with more pulses applied that are harder, ATRAC seems to lock up then unpulse to let the wheels move if that makes any sense. To put it another way... TRAC lets you keep spinning then pulses the brakes more and more. ATRAC locks up the brakes at the first sign of spin, hold you in place, then slowly tries to allow movement through releasing the brake more, unless it spins, then it locks up fully and tries to release again.

On steep uphills TRAC gives a slight rocking sensation before movement. ATRAC does not.

Id really like more peoples input on how the systems actually work. I wish I could find the spots where I know I can get them to react a certain way and film the difference in TRAC and ATRAC in action from the outside. I suppose I could be worng and intermpreting what I am feeling incorrectly but thats how it feels like they work.

Anyone else have experiences to share that might shed light on how they operate?

 

Thanks DevL for your observations... I am not sure I understand everything you experienced, but it is great that you took your Taco out and played with it and the various traction options the Off Road 4x4 has.

It is important to know gang, that the term 'brake' used is not to be confused with stopping the vehicle brake, but instead means braking a spinning tire to slow it down so the other tire on that axle gets power (TRAC) or braking a spinning tire to match it with the opposite tire (like a locker makes both tires rotate the same).

A-TRAC does not brake both tires on the same axle, only one of the two, to match rotation... this makes the traction tire the boss. Open differentials without A-TRAC make the non-traction tire the boss... This is why one tire spins and the other does nothing to move you (on trucks without traction control or lockers).

I found on steep climbs (like One Tri Hill where I was video'd using A-TRAC) that I just put my foot into it (giving it gas) and the A-TRAC becomes a tractor...

Just don't give up if you are climbing and come to a stop either from steepness or from a rock in the way... Just mash the accelerator and let the A-TRAC become the automatic locker and crawl over and up!

 

WOW David!!

Awesome thread. Toyota should hire you as a sales manager, so SOMEONE at the dealerships could actually explain the 4wd functions of Tacomas/Tundras.

-TV

 

Thank you... I do need some extra work so I can continue to go four wheeling! (Wet weather and bad economy suck in my business... landscape irrigation systems!)

 

This is great! I use my junk all the time but it can get confusing what is on and what is off. Gonna take your info and make a little laminated reference card to keep in the center console.

Awsome info!

Thanks

 

You're very welcome!

BGrutter made this up, it is a few pages back in this thread:

 

Hell yahyuh! Awsome....I was making mine at work this morning and had all kinds of pretty highlights and junk......couldnt get the printer to connect to the network

Thanks again man!

 

wow if I get one of these trucks (debating between a Frontier, Tacoma, and pre-A-track Tacoma) I'll be printing out a cheat sheet...

 

It helps, but only if you want to 'play' with the trucks MANY choices for traction control.

If it helps, you really don't need to do anything other than press the A-TRAC button once (the first time you are in L4). The other standard drive modes work fine!

1) H2 (TRAC with engine regulation is the standard mode, AUTO LSD [TRAC without engine regulation] is mostly beneficial to non-4WD owners, because they don't have 4WD... which is what we would use if the back tires lose traction)

2) H4 (TRAC without engine regulation is the standard mode)

3) L4 (here it makes no sense to leave the differentials open, as low range is only used for the most severe traction needs... so push the A-TRAC button).

If for any reason you don't want improved traction in H2 or H4, then you can have open differentials like the pre-'09 Off Road Tacomas by holding down the VSC button for a few seconds, while stopped.

Choices... we have 9 drive modes, but the 3 I listed above will do the most for you!

 

I was driving on a sandy trail that had sharp turns and the terrain was at an angle. I was in H4, Drive.

Twice the truck would slide sideways and bug down into the sand during these turns. I had to go into Reverse and then build up momentum to get me thru.

I then tried H4 in 2nd Gear. I noticed I hade beter success as it felt the truck had more power to get me through those sandy turns.

Is that the correct gear to use on sand? I was thinking of using L4 but I thought that make the truck sink down faster.

 

The correct gear is the one that works for you! I have an automatic, so it finds the right gear automatically.

There are so many different kinds of sand and then temperature and humidity affect sand driving, as well. I just got home last night from 3 days in Baja, on the beach with the deepest/ most difficult to drive-on sand... and the trick there for most is lowering the air pressure to 10-15 psi on all 4 tires, then use H4 and keep momentum up... Avoid spinning tires at all cost. TRAC does excellent in sand as tire spin (that only gets you stuck) is avoided. Should you get stuck, then L4 with A-TRAC can be tried... but be very light on the gas pedal... feather the truck out. In the end, it really is all about air pressure and floatation. Less is best, in sand!

 

Word. Sub'd.

 

Thanks for starting this easy to understand thread Can you explain more about open differential mode and when you would use it? Thanks.

 

I personally have no use for the 'old style' differential option... but it is there because Toyota gives us everything to have fun in our Tacomas!

Seriously, if you are in 4WD-Hi, and zipping around in arroyos (dry washes) or across the desert... the VSC beeper goes off a lot... and if you don't need the limited slip then going to VSC OFF MODE (Open Differentials) will silence the beeper (up to a point it thinks you are about to roll the truck).

 

FYI, (not gonna read thru the whole thread to figure out if you figured it out My 07 does not have the auto LSD through braking. Its full posi, and its very evident everytime I pull out onto the street in the morning.

 

Hi Brian, FYI: the title of this thread is "A-TRAC/TRAC/AUTO LSD Explained", so you didn't need to even open the thread unless you wanted to read about THOSE systems that use the brakes (and not clutches inside a differential) to slow a useless, spinning tire(s) so that the other(s) can move the truck. The three named drive systems have been standard on all 4WD Off Road Tacomas since the 2009 model. Have a nice day!

 

That statement is incorrect.
Factory LSD "speeds up" tire with less spin. Thats why it wastes no fuel. Dont believe me grab Toyota Eng and ask them.