auto LSD- what is the point?

The electronic thing is way over rated, I'm pissed cus the rear differential does really nothing until u use the rear E-locker. I rather have a G80, at least then the non drive tire would hook up and pull too, for a short time.

who knows about that locker from Aulburn gears?

 

I try always to thank this forum for helping me learn the system that the manual or dealership couldn't explain! Thanks Hemi for the info you provide... now, I am all ears Hemi... this will be a good addition over on the Sport vs. Off Road thread, too!

 

Okay. I am crystal clear on when to use TRAC-OFF Mode now. And moreover, I understand exactly how it works.

I am curious about something you wrote. While I would agree that the TRAC software algorithms are essentially the same in 2WD or 4WD(H4), the documentation states that while in 4WD(H4)(with respect to TRAC), that engine output is not regulated.

If that logic holds true, then when I shift into 4WD(H4) and should the TRAC feature be activated would it not then behave exactly as Auto LSD (Aggressive braking of spinning wheels when traction differences are detected between left and right wheels when starting from a stop.)?

Or is the documentation wrong and engine output regulated while TRAC is active in 4WD(H4)?

Sorry to digress but I don't think anyone else in this thread cares.

 

I was thinking that AUTO LSD worked more like A-TRAC using a hydraulic booster... and TRAC uses a vacuum booster ... why it works more when you are moving beyond crawl speed or after start off.

 

That's why I think TRAC and AUTO LSD are powered by different sources.

A-TRAC and AUTO LSD use a hydraulic brake booster for aggressive braking of loose wheels.

TRAC uses a vacuum brake booster for gradual braking of loose wheels and regulated power output. In H4 there is no output power regulation.

 

David, I am inclined to think that there is only one source for all our traction features. And that source is comprised of two distinct systems and depending on the model of truck is either:

1. Vacuum Brake booster and brake control system.
2. Hydraulic Brake booster and brake control system.

Check out this diagram

After looking at the diagram, I think it's safe to say that that those of us with A-TRAC, DAC, HAC, features in our truck have the hydraulic type of booster.

 

YES... my bad with the terminology ... I edited the words 'engine vacuum' to vacuum brake booster. Thank you!

 

I was saying the Auto Lsd is the same as TRAC in 4WD. Different algorithms are used for TRAC with throttle regulation.

Yes

No engine output regulation.

 

And the difference is that the Sport model uses the vacuum brake booster, (which you already know), but this places a peak brake application limit. As well it is not terribly difficult to throttle through the brake intervention with the Non Off Road (NOR) model, especially if the brakes get wet. Combine this with a situation where it is trying to control both axles at the same time, and it is noticeable. This is the biggest drawback. One way to mitigate this effect is to run a lower gear / higher rpm, which generates more manifold vacuum. The OR model has the hydraulic booster, which overcomes both these issues, and allow TRAC to be much more capable.
A-TRAC is most impressive to me, because the Hydraulic brake booster generates enough braking force to arrest nearly and amount of power. And that is my opinion on why there is no TRAC in 4 low on the NOR trucks.

 

Okay, if this is the case: "I was saying the Auto Lsd is the same as TRAC in 4WD. Different algorithms are used for TRAC with throttle regulation"...

Then how is/ or is A-TRAC (in L4) different than TRAC (in H4) and AUTO LSD (in H2)... if all three use the hydraulic brake booster?

I was very impressed with TRAC in H4 in how it took me over deep sand I have driven hundreds of times in my other Tacomas without the need to lower tire pressure (for the first time).

Thank you Hemi!

 

In simple terms, TRAC in 4H limits the torque being sent by incrementally increasing brake system pressure. A-TRAC immediately applies full brake pressure (if required) to match left to right wheel rotational speed.A-TRAC monitors the wheels rotational position, whereas TRAC monitors wheel rpm.
Limited slip vs pseudo Locker.

Also

Toyota Tech Manual - 2009

Auto LSD
(Limited Slip Differential)
Briefly pressing the VSC OFF switch in normal mode enters TRAC-OFF
mode, allowing the Auto LSD to operate. The Auto LSD achieves a
function equivalent to that of an LSD system through the use of the TRAC.
The Auto LSD applies brake hydraulic pressure to a slipping wheel to
reduce the difference in rotation speed between the left and right drive
wheels. This causes driving torque to be transmitted to the wheel opposite​

the slipping wheel.

 

Thanks Hemi... please answer these to make sure I understand fully your data.. I appreciate this!:

Is it correct to say that for us with Off Road TRDs, that AUTO LSD in H2 (TRAC OFF) mode, 4H (TRAC ON), and L4 (A-TRAC ON) all have the SAME hydraulic brake booster action with the only difference being 2WD, 4WD HIGH RANGE, and 4WD LOW RANGE being gearing/ transfer case choice?

That in 2WD, the difference between TRAC ON and AUTO LSD (or TRAC OFF) is that TRAC ON has throttle/ engine output intervention/ regulation?

In other words, TRAC ON in H2 is also conrtrolled by the hydraulic booster...

Is there no vacuum brake booster operating the drive modes in the TRD Off Road Tacomas (2009+)?

Many thanks... I think this should put the mystery to rest.

 

David,

I know your question is directed to Hemi, but I think I can answer the riddle for you too.

Yes. That was my question a few posts ago. It appears that it is indeed the only difference. And to Hemi's credit, he stated it in this thread in post #7 back in November '09. He also reiterated it post #81 as well.

With regards to the brake booster type, I understand that there are two types. Our truck model has one type or the other but not both. It is either hydraulic or vacuum type. Those that have A-TRAC have the hydraulic booster type, those that do not have A-TRAC have the vacuum booster type.

Yes.

Correct. (TRD Off Road Tacomas (2009+)) = It is hydraulic type booster only.


Look at the underlined text below.

From the Toyota Tech Manual - 2009:

• The vacuum brake booster and the brake control system (ABS with EBD, Brake Assist, TRAC, VSC and Auto LSD) are provided as standard on all models.

• The hydraulic brake booster and the brake control system (ABS with EBD, Brake Assist, TRAC, A-TRAC, VSC, Auto LSD, Downhill Assist Control and Hill-start Assist Control) are no longer available as option on all models but provided as an option on 4WD models with the 1GR-FE engine (except the super long wheelbase models).

• A brake master cylinder, whose structure has been optimized, is provided on the vacuum brake booster models to achieve a weight reduction.

• An A-TRAC switch has been added to the hydraulic brake booster models, which allows the A-TRAC to operate according to the road surface condition even if rear diff. lock mode is selected.

Thanks Hemi, David, and others. I have enjoyed this thread a lot. It has helped me understand my trucks traction systems much better than before.

 

Close but no.
In simple terms, TRAC in 4H limits the torque being sent by incrementally increasing brake system pressure. A-TRAC immediately applies full brake pressure (if required) to match left to right wheel rotational speed.A-TRAC monitors the wheels rotational position, whereas TRAC monitors wheel rpm.
Limited slip (TRAC) vs pseudo Locker (A-TRAC)

Yes

Controlled by the VSC computer. The hydraulic booster merely provides the brake fluid pressure to the solenoids, (for all brake related actions) which direct and hold the fluid pressure, which generates braking force.

No Vacuum boost at all on TRD OR's. Boost is provided by a dedicated hydraulic pump.

 

Awesome Crom and Hemi... Thank you... Knowledge is awesome!

Now, let's go four wheeling!

 

^ Yes. (Skid control ECU), it is attached to the brake actuator. Sorry, David I misread that portion of your post.

Time to hit up Anza-Borrego!

 

Yes, Borrego would be good... Baja would be better...

As for this discussion, since the OFF ROAD Tacomas have the hydraulic Brake Booster and the SPORT models only have the vacuum brake booster, this must be why they (the Sports) don't get as big a thrill from their Auto LSD or TRAC system as we do in our Off Road Tacomas... ? Is the hydraulic booster only on the 4WD Off Roads (that have A-TRAC)*? If that's the case, the 4WD Off Road TRDs really are in their own class!

* I just looked at the chart and see it is only on the 4WDs

 

David, I think the short answer is yes.

It is an interesting question, because the technical document seems to suggest that the hydraulic booster was available as an option on previous model (pre 2009) Tacomas. I am curious about that. If I remember I'll try to find an experienced competent Toyota technician who may be able to answer that question for us.

Also, when Hemi proposed his question:

I did not answer him directly because I wasn't sure. I suggested the brake booster type because it was the only fundamental difference I could find. He also caused me to read with greater scrutiny which helped me absorb more and further my understanding. And for that I am grateful.

 

It sure makes a difference reading the owner's manual and the tech sheets when we can test our trucks or get good, complete answers to the parts that are not clear... or that we just don't 'get' the first time around.

I know Hemi has probably answered these questions before, in other threads, maybe in a different way... I hope he understands that we really want to learn, and it might take some of us more than one time around to get it straight!

I made my signature based on tech sheets, Tacoma World posts, and personal trials BECAUSE I wanted a clear 'black & white' explanation of the many drive modes we have (at least those of us with '09 or newer 4WD TRD OFF ROAD Tacomas).

The hydraulic brake booster that the A-TRAC equiped Tacomas have is a big kick in the performance of the traction systems in H4 (TRAC) and H2 (AUTO LSD), as well... I just don't see using AUTO LSD when we so easily can put it in 4WD for traction assit? Maybe Toyota will put the hydraulic brake booster in 2WD and Sport 4WD Tacomas someday to improve their AUTO LSD and TRAC operation?

 

Last Saturday in Borrego, lot's of fun four wheeling and two wheeling as well testing AUTO LSD vs. TRAC in H2.

As I suspected... AUTO LSD is like Posi Traction in the rear end... I got two roosters of sand at suddon acceleration in an arroyo (dry wash)... the same as if the rear was locked.

Like A-TRAC in L4, AUTO LSD in H2 is a strong 'locker-like' rear limited slip differential.

Turning TRAC back on in H2 (AUTO LSD OFF) the same rapid acceleation was regulated to prevent one tire from spinning too much... but one would get torque first before torque was split between both tires (as they both had equal traction conditions).

AUTO LSD is like a rear locker and A-TRAC is like front and rear locker.
TRAC in H4 is also very strong, much more so than TRAC in H2.

On a sand dune climb, I reached the same point in H4 (TRAC on) and L4 with A-TRAC on. When I turned TRAC and VSC OFF in H4 (open differentials) and also in L4 (A-TRAC off/ open diffs.) they both made it only about half as far on the dune.

Fun in the desert sun... with Toyota and AUTO LSD, Traction Control and Active Traction Control!