TRAC functions: on and off

[mywife's4runner]

My wife just picked up our(read her) new 2011 limited 4wd. I have been trying to figure out how all the 4wd functions work and have learned alot. my question still is when TRAC is on it reduces engine power and moves torque to other wheel right on both front and back axles?, OK when I turn it off, I keep power and can spin the wheels, but is it now a open differential or do I still get limited slip, and is it on both axles. If so what is the difference between that and A-trac when in 4low?
:rtfm:
I could not seem to find the answer here and I RTFM, and TFM sucks :rtfm:

Thanks

 

[mywife's4runner]

Come On guys no one has an answer. I know I am new and don't know alot abou this new system. But I seache this site and the net and can not find the answer. I am not asking how the system works. I am ask how the diffs preform when the TRAC is off. If it was a mechnical system I would know how it works but this electronic stuff is different .
Also when in 4low why in the world would you want atrac off. If it is off then you would have open diffs right? So why leave it off?
I can see why you would want to turn Trac off b/c if modulates engine power, but it seems like if you do, then you loose your " simulated limited slip". That seems kinda of counter productive.
I just want confirmation this is right and why Toyota would do this? Cost, safety or wear and tear issues? What do y'all think

 

[JB.]

Toyota has 1 way of emulating limited slip diffs in front or rear -- braking the spinning wheel. If that function is disabled, the diffs are open.

Easiest test I know. On snowy ground, put front wheels against tall, dense snow berm. Start spinning the wheels and you'll know right away if it's going to try to brake any of them.

 

[mywife's4runner]

Toyota has 1 way of emulating limited slip diffs in front or rear -- braking the spinning wheel. If that function is disabled, the diffs are open.

Easiest test I know. On snowy ground, put front wheels against tall, dense snow berm. Start spinning the wheels and you'll know right away if it's going to try to brake any of them.

the snow thing is going to be tough? doesn't snow much here west texas, and it gone in a day or two. I am going to have a tough time testing it out anytime soon that why i ask

 

[JasonCz]

Also when in 4low why in the world would you want atrac off. If it is off then you would have open diffs right? So why leave it off?

I can answer this from recent experience. I have a 2010 SR5 4x4. I took a ride out in a national forest where there was 10-12" of fresh snow ontop of a relatively rough dirt trail. The trail was slightly off camber with a steep dropoff at one side.

I had the vehicle in 4L with ATRAC engaged, and the car would every so often start turning to the right toward the dropoff even though I was steering to the left. I about crapped in my pants a few times. I noticed that if I let off the gas when this happened it would straighten up.

When I got out to inspect the conditions, I found that there was ice under the snow only on the right side of the trail. The computer was sensing the wheels on the right slipping so it would brake only that side of the vehicle to transfer power to the wheels that were not slipping which would push me right. Once I turned ATRAC off everything straightened out just fine.

In my opinion ATRAC should only be used when already stuck and one wheel spinning or atleast in locations where sideways movement of the vehicle wouldn't have any serious consequences. Although Toyota markets it as a true replacement for a locking diff, it does not perform similarly in all conditions. If I would have had a true locking diff in the situation above, both rear wheels would spin whether they had traction or not, so I wouldn't be pushed to one side (or not nearly as much).

An ARB rear locker is in my longterm plans.