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

Reading this, in 4-HI there is no way to turn VSC off and leave TRAC on correct? Is this a true statement?


For the yellow wire mod, it allows TRAC in 4-LO but does it also keep VSC on or does it turn it off since 4-LO is selected, it just never gets comfirmation that it is in 4-LO.

 

vsc is always on. even when its off it will still step in if you get real sideways unless you are in factory 4lo...

vsc and trac uses the same system so if you disable vsc it wont use the brakes to regain traction thus elliminating trac

in 4hi and 4lo you can do the yellow wire mod, it will beep and buzz but keep skinny pedal down and you will make it through

if you want to play in 4wd without any vsc dont put a switch on the yellow wire mod to disable the mod. 4lo from the factory has no vsc or trac

 

This chart (posted on the first page of this thread) pretty well shows you that VSC and TRAC are tied together in 4WD-HI...

 

such a good thread and write up as well.... such good info alot of sources really good stuff!!!!!!!!! i have an 11 trd offroad and have been fooling around off road reading the manual and playing with all the modes and i have to say the manual isnt too clear on all of the functions and is a little confusing .... anyway got alot of good info and cleared up a couple of things on it ... much easier to understand with other people's write up... good stuff....

 

Glad it helped! Have fun with it all!

 

David, what is the difference between a 2007 4x4 Off Road truck equipped with the optional TRAC/HAC/DAC/AUTO LSD and hydraulic brake booster, compared to a 2009 4x4 Off Road truck equipped with the standard A-TRAC/TRAC/HAC/DAC/AUTO LSD and hydraulic brake booster?

Other than the button and the name A-TRAC, is there a separate A-TRAC ECU or something that was added to the 2009+? All I've read is that there is a hydraulic brake booster. Which some pre-09 trucks have.

I ask because my 2007 4x4 Off Road allows for TRAC in 4L, and in my opinion it is very strong (similar to the way you guys describe A-TRAC in 4L). One difference I've found is that I cannot be in 4L + RR dif lock + TRAC. Luckily there's a mod for that.

I tested the same hill three ways.

4H TRAC OFF / VSC OFF - Could not make it. I sat there spinning.
4L RR Dif Locked / TRAC OFF / VSC OFF - Crawled right up.
4L TRAC ON / VSC OFF - Crawled right up with very little slippage. The brakes grabbed the slipping tire(s) immediately.

Thanks.

 

That is a great question... since A-TRAC has been installed on variouis Toyota products (Land Cruiser, Lexus, FJ Cruiser, etc.) long before the Tacoma Off Road got it in 2009, I don't know why they wouldn't call it A-TRAC if what you have really was that? The A-TRAC system is more advanced then the TRAC system... A-TRAC matches tire rotation across an axle and TRAC only slows down a faster tire of the two on an axle. The hydraulic brake booster seems to slow it down quicker and better. So, an Off Road 4WD TRD TRAC (H4) would appear to be stronger than a Sport or SR5 TRAC for this reason.

You do seem to have TRAC (at least) in L4, and that is what the '09+ non Off Road 4WDs get with the 4-Low trac Mod.

When I was doing my various 'tests' out in Ocotillo Wells, I did find that H4 TRAC was almost as good as L4 A-TRAC... and both of those were a bit better than L4 RR Locker (no A-TRAC). The worst 4WD modes were L4 open diff. and H4 open diff (VSC OFF Mode).

In my research limited slip front and back was superior in traction to open diff.s and the rear locker.

 

Thanks for the response, David. I realize this is more of a 09+ thread, so I appreciate your patience in answering my questions. You seem to be one of the more knowledgeable ones on the subject, so I posted here.

I was excited to see TRAC available in 4L on my 2007 OR, as well as the hydraulic brake booster (HBB), and I want to learn as much as I can. I also noticed there was confusion on TacomaWorld that the HBB was only available on 09+ OR models. I wanted to shed some light on that subject.

Good point. They didn't call HBB 4L TRAC, A-TRAC on Tacomas until 2009, so I understand why A-TRAC sounds like it is a definitively different system. Which is what I'm trying to find out. Is it, or is it a name and an extra button that allows traction control in 4L with the RR Locked? I am not the only one that shares this curiosity (read his definition of A-TRAC). Also, here. It seems to me like this is a question for someone at Toyota USA.

What you explained above have been my findings during testing. Yoytoda has a video of his truck after the yellow wire mod that allows him to run TRAC in 4L, but I noticed on his truck it takes a lot of wheel-spin for TRAC to kick in. My 07 OR with HBB TRAC on in 4L is much much quicker in stopping the spinning wheel. Like I mentioned earlier, it's damn near immediate. The HBB makes a lot of noise as soon as a tire slips. It sounds exactly like when I use the Downhill Assist Control.

Again, I wonder if Toyota would be kind enough to answer what other equipment related to A-TRAC 09+ Off Roads have, that pre-09 HBB TRAC trucks do or don't have.

That makes me feel pretty good about how the HBB TRAC in 4L should work with the lower wheel speed and higher torque of 4L. Whether or not A-TRAC and HBB TRAC in 4L are the same, it's a fantastic system. What I need to do now, is do the mod that allows for HBB TRAC 4L with the RR Dif locked. or if it crosses over from the FJ __________________________________________

More info to add to your thread if you are interested, David K:

(I will exclude "VSC OFF MODE" and "TRAC OFF MODE" since I am not sure if that image carries over to the 2007-2008. I will only show what is on or off)

2007-2008 4x4 Off Road equipped with TRAC/HAC/DAC/AUTO-LSD

1) 2WD: VSC and TRAC active, engine regulated ('Limited Slip Lite').

2) 2WD: 'AUTO LSD' ('TRAC OFF'). No engine regulation for 'strong' limited slip.

3) 2WD: 'VSC OFF' and 'TRAC OFF' for 'open differential'.

4) 4WD-Hi: 'VSC OFF' and TRAC active. No engine regulation for 'strong' limited slip front and rear.

5) 4WD-Hi: 'VSC OFF' and 'TRAC OFF' for 'open differentials'.

6) 4WD-Lo: 'VSC OFF' and TRAC active. No engine regulation for 'strong' limited slip front and rear'.

7) 4WD-Lo: 'VSC OFF' and 'TRAC OFF' for 'open differentials'.

8) 4WD-Lo: 'VSC OFF' Rear Differential Locked and open front differential (TRAC off).


(Holy crap that is a wall of text)

 

GP3, where in California are you? I am in Oceanside and we should go out and compare our trucks in 4WD!

One thing I was wondering if you got it figured, was the connection between A-TRAC and the Rear Locker?: Originally (on FJs, etc.) you could not have both on at the same time (A-TRAC I or 1.0 maybe? lol). A-TRAC II or 2.0 which I think is the kind we got in the '09+ Tacomas does allow you to have both the A-TRAC on and the rear differential locked.

The A-TRAC is active up to 3 mph when the rear is locked. I found this mode ideal in the snow last February... Since A-TRAC really only 'works' when you stop moving from tire spin... the 3 mph limit is like no issue... you are always under 3 mph when you stop moving from traction loss! Anyway, I don't use the rear locker typically because the A-TRAC is so much more effective and intellegent (only 'locks' a wheel if it needs to be), but it is good to use all the modes periodically to keep them 'lubed', etc.

The rear locker worked well off road in snow/ mud and a couple times when the drifts got deep, I could hear the A-TRAC go to work... it makes some intersting noises... just briefly.

Now, there may be snow or mud situation that you want a tire to spin as in to grab fresh terrain to bite into... then, turn A-TRAC off and your one low traction tire will spin freely... and you should turn your steering wheel left-right-left to grab for traction. I only recommend this if you can drive no further with A-TRAC (I have yet to find that condition, however!).

 

I will PM you.

Yeah I have noticed that on early FJs. That's a good way to explain it. I have the v1.0 or something very similar. They couldn't enable ATRAC with the locker just like I can't enable TRAC with the locker.

 

To add to this, when VSC is OFF, it will not turn back on when you go over a certain speed. I've noticed some people say it turns back on when you go over 30mph. I tested that this morning up to 50mph. It never turned back on.

 

NO... an open differential transfers power to a tire that spins easy (has less traction)... usually how you get stuck.

4WD adds the front, but with the same open differential... so in a bad stuck, one tire in front and one tire in back spins and you go nowhere.

A-TRAC has spin sensors, and if any tire begins to spin, the computer applies the exact amount of braking to that tire to eqaulize it with the opposite tire that has traction. A locker does this with gears in the differential, but there are no sensors so you need to disengage the locker as soon as you are unstuck in order to steer easily.

What happens with either A-TRAC or a locker is that both tires on an axle rotate at the same speed with equal power (torque)... and that is what moves you up, trough, or over an obsticle.

A limited slip differential or traction control slows down a spinning tire so more power can transfer to the traction tire... It can help but isn't as complete a equalizing of power as a locker or A-TRAC.

 

So, I didn't read all of the posts. I've done most of my off-roading in HMMWVs, and they taught us to use "brake pedal modulation" when we were getting slippage. It sounds to me like ATRAC does the same thing just electronically.

 

Except A-TRAC will apply brake pressure just to the spinning tire only... and at a rate equal to the traction of the other tire... so both get equal power and rotare the same speed... just like a locker does, but automatically... and frees up when you are past the stuck spot so you can steer as needed.

 

The A-TRAC is 'active' only under 3 mph if you lock the rear... It may have been a case you needed some front tire spin to grab fresh snow/ mud if you were easing into the snow. The key to the system is to really give it the throttle... make it know you are the boss... put your pedal to the medal and overcome the stuck.

Try A-TRAC only next time you are in Low Range (don't lock the rear)... Remember it is traction control on all 4 tires, not just the front or just the back. Turn your Tacoma into a tank with A-TRAC!

If you find a condition where it is not working for you... turn it off and lock the rear... The rear diff. locker is for emegency use only per Toyota, afterall... A-TRAC can be used all the time you are in low range, as it is active only when a tire spins away... or wants to spin if we let it!

 

I'm really lookin forward to trying all of this when I graduate from my base to a 2012. Also, I've been trying to explain all of these things to my wife. Her 08 4runner SE has all of the cool stuff. When I start explaining the center diff her eyes glaze over. Oh well