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

Nice... even better is if someone with access to Toyota tech manuals can provide a chart like we had for the 2009-2011 Tacomas...

 

I tried the sandy spots around here, but they are too wet (making them not soft) or too short in length to really show the systems at work.

So the earliest that I can do the test will be this weekend. I know some real soft sand with long sections that should be perfect for the test. But they are about an hours drive from here.

PaulThePhotographer

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Hmmmm, Maybe a different Test might be better.

Something like this, that I like to do with our FJC.
(I would put the FJC like this in 4LO and shut off everything and tell new people I am taking for a ride, that we are stuck. Because in 4 LO with everything OFF only the two wheels in the air spin.)



Notice TWO opposite tires are off the ground at The same time.

So by the chart above! (Caveat: I realize that this photo the FJC is on a hill that would effect the test. But I have a different spot where the FJC is on level ground and I can do this same trick. So think of my examples being tested on level ground.)

When I am in 4Hi and I have pressed the VCS Button for more than 3 seconds, the Tacoma should NOT be able to move when situated like the FJC in the Photo. The two tires in the air should spin by themselves and the tires on the ground NOT spin! Correct????

But with only a Quick Push of the VSC button the Auto LSD (would still be on) would make BOTH rear tires turn and push the Tacoma forward. But ONLY one Front tire would spin, because Trac would be off. Correct???

And in "Normal" mode all four tires should spin/turn in this situation. Correct?

I might be able to do this test sooner?

PaulThePhotographer

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To answer your questions.

Correct. Completely open diifs; zero traction control or VSC.

Incorrect. In previous years, a quick press would return you to Normal Mode (TRAC on/VSC on). Also, Auto LSD only came on in 2wd. Never in 4wd.

This is where 2012 might be different. Putting your truck in the FJ's position, and running down the list I suggested will tell us the difference.

Correct.

 

Remember that TRAC in H4 was the same as AUTO LSD in H2 (2009-2011), ie. no engine regulation.

AUTO LSD or TRAC are just "limited slip" systems, which means the free tires will still spin, but not 100% (as with open differentials) as the system transfers power to the traction tires by applying brake force against the spinning tire. That may not be enough if the conditions are severe to get you moving. That is where A-TRAC or Lockers come into play. They both match power across the axle, so both tires turn equally. A-TRAC does it with brakes and lockers do it with gears.

 

I have the opinion that hydraulic brake boosted 4 High TRAC (not the vacuum boosted 4 High TRAC that SR5's and Sports have) has the same braking effect as ATRAC, but the difference you feel helping you out of a precarious off-road spot is the extra torque from 4 Low (and ability to use with RR Locker). That's a whole 'nother can of worms, and frankly, there's no documentation saying otherwise, but we can leave that for a future discussion while we test the 2012.

 

While I do agree that the Off Road 4WDs (with a hydraulic brake booster) have perhaps a stronger TRAC limited slip than all other Tacomas, I do believe the A-TRAC is a totally different system than TRAC in H4. TRAC limits spin and A-TRAC stops spin, and only the hydraulic booster has enough force for that. There also are some very 'interesting' sounds made by the A-TRAC you never hear with TRAC (grinding, popping, ticking, weird stuff).

A-TRAC is so much like having front and rear lockers on in the way it crawls the truck over the most difficult, poor tracking conditions... makes the truck feel like a tank or tractor... with only the body height or tire size limiting where the truck can go.

 

Wait for it...wait for it...

 

Right, but I think the extra noise is because the brake system has to apply much more force to combat the added torque of 4 Low. Also, I think the wheels stop because of the low wheel-speed you see in 4 Low.

Have you seen, or is there video, of a hydraulic brake boosted truck in 4 High with TRAC on where TRAC is doing it's job? I'd like to see it. I'd bet that the less-traction wheels do indeed stop if the wheel with traction is slow enough to warrant stopping the less-traction wheel. You just don't always see those low-speed, low-traction scenarios in 4 High.

 

Only Shemp knows.

 

PhotoPaul, the big question on our 2012 is the options for 4H. I read up on different threads like these hoping to learn about the different ways to use these options for an Off Road 4x4. I was under the impression that while in 4H the best option for traction was to go straight from 2WD normal driving mode into 4H and like this I would have TRAC on giving me limited slip front and rear with no engine regulation. Well I tried to pull a car out of a rather light weight stuck situation and found out differently. While I was pulling the car in 4H with no buttons pushed I started getting engine regulation killing my power. I hit the button once while in 4H and seen the "TRAC OFF" light. TRAC (according to what I have read) is NOT supposed to regulate engine power. This is where the BIG question comes in because in previous years there was no engine regulation in 4H with TRAC ON. But Im all but sure that I DID have it.

 

Yep. Using your thread and your findings, I made up a step by step list to test 4 High.

I'm hoping he's going to use it so we can put the 2012 modes to rest. It's the easiest, most systematic way to test it.

 

My new quote! LMAO!!!!!!!!

 

It will never be anywhere as good, but its better than nothing i guess

 

What the hell are you smoking down there..you must be bored and trolling on purpose with your last statement. What a whack job

 

Im gonna go get an 09+ offroad and follow you to the hammers. ok Monkey?

 

I double dog dare you

 

That was set up and supposed to happen with another guy, but never did.

Anyone know why?

 

Would you be referring to me? Still waiting. Monkey and I have ran several Hammers trails with our IFS trucks together. No sweat off my back.

 

That excuse still flies? It's Fall now.

This weekend looks perfect .