How does ATRAC work??

I know this thread is old BUT I pretty much understand ATRAC as explained on this thread.

According to another thread posted on this site, this was my understanding of ATRAC and Auto LSD. I thought ATRAC cut engine power and uses the brakes?? If I hit the Auto LSD button on my 07 2wd 4runner, it only uses brakes and doesn't cut engine power.

Can someone please clarify because now I am confused.
 
ATRAC is used to brake the spinning wheel to act like a limited slip differential, so that power is moved to the non spinning wheel. TRAC is traction control and that is what cuts engine power if you wheels are spinning such as starting from a stop sign on snow/ice. Auto LSD will turn on/off the ATRAC function for your rear wheels if I'm not mistaken. On your 2WD since only the rear wheels will get power, if one tire has traction and the other doesn't ATRAC would likely kick in, if neither of them have traction TRAC would kick in to keep you from spinning your tires (both at the same time).
 
So my 07 2wd t4r has the following safety functions?

ATRAC
Traction control
ABS
VSC
Auto LSD

I always thought ATRAC was what toyota called their traction control. I know with some manufacturers, traction control uses the braking, cuts power, or a combination of both.
 
Not sure about the 2wd but the 4x4s should. But you need to have the center diff lock enabled.

Some of the more recent models like 2006+ might have a VSC and Atrac button. This lets you disable VSC even though you aren't in center diff lock 4x4 mode, or disable Atrac even though you are in 4x4 center diff lock mode.
 
CAN-03runner said:
Not sure about the 2wd but the 4x4s should. But you need to have the center diff lock enabled.

Some of the more recent models like 2006+ might have a VSC and Atrac button. This lets you disable VSC even though you aren't in center diff lock 4x4 mode, or disable Atrac even though you are in 4x4 center diff lock mode.
Click to expand...

thanks!
 
ProspectiveBuyer said:
Sorry for bumping an old thread, that's what you get when you use the search function!

ATRAC does not seem to work all that well, it certainly does not behave like a locked diff, in this video the rear wheels do spin at very different speeds:

https://www.youtube.com/watch?v=85n5Ouz4jRA
Click to expand...

Have you tried it? It does work very well in my experience. I haven't looked at the wheel speeds because I'm driving, but it gets me going. It acts more like a limited slip diff than a locking one. And it pulses the brakes on and off rather than modulating braking force and speed smoothly. It's kind of like ABS, and it's the same system that actuates the brakes for both.

I've found it works best for crawling over obstacles on a trail, rather than going through snow with bad tires. I've been slightly stuck (had to back up a bit) on a snowy trail like that, but a truck with lockers might not have much of an easier time with the same tires.

I did a trail with a friend who had a rear locker and no ATRAC, and I had an easier time on some of the obstacles. He had All Terrain tires, and I just had LTX M/S2 tires which don't have very aggressive tread.

Also, if you rev the engine, it probably won't work as well. It seems to work best for slow and steady driving.
 
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Yeah. It's not a locker. I assume this guy wanted to show how it worked. Not so much to prove its worth, but simply to illustrate the behavior. Generally when traction is pretty consistent among all 4 tires, such as when in the snow, ATRAC is not super valuable. When you have certain wheels with a lot more bite, it is a very valuable tool, such as when offroading on uneven/inconsistent terrain. Compared to a vehicle with an open set of diffs without a similar traction aiding device offroad, the ATRAC equipped vehicle is far superior.
 
poncharello said:
Ignore the music, but found this was a better example of A-trac. Particularly the second half of the video.

https://www.youtube.com/watch?v=fLI0rtbiTEQ
Click to expand...

That's pretty impressive. So to be clear, the SR5 does NOT have a locking rear diff, but ATRAC (by braking the slipping wheel) effectively "locks" both the front and rear differentials.

Can you physically lock the front and rear differentials in the Trail Edition?
 
ProspectiveBuyer said:
That's pretty impressive. So to be clear, the SR5 does NOT have a locking rear diff, but ATRAC (by braking the slipping wheel) effectively "locks" both the front and rear differentials.

Can you physically lock the front and rear differentials in the Trail Edition?
Click to expand...
For the 4th gen, only the 2009 Trail Edition had an electronic locking rear differential, but that model is extremely rare (probably only a few thousand sold in the US). And if the e-locker on the Tacoma is the same part, and it's not known to be the most reliable. Some people add aftermarket locking differentials, such as ARB air lockers. They are very strong, but relatively expensive, so probably not worth it unless you know you need it.

I don't know about the 5th gen. But I know they made the rear differential stronger, so I wouldn't worry about the reliability of an e-locker if it has one as an option.
 
ProspectiveBuyer said:
That's pretty impressive. So to be clear, the SR5 does NOT have a locking rear diff, but ATRAC (by braking the slipping wheel) effectively "locks" both the front and rear differentials.

Can you physically lock the front and rear differentials in the Trail Edition?
Click to expand...

Don't think of it as locking the differential so much as stopping the spinning tire. No mechanical wizardry is within the differential itself. There is no locking taking place. Rather when the brake slows/stops a spinning wheel power is diverted to the opposite wheel to search for traction on that side.

The biggest gripe I have with ATRAC on our 4runners (I understand FJs may be a little more aggressive in engagement) is that you need some wheel spin to engage the functionality. When you're in a precarious position, wheel spin is not something you necessarily want. That combined with the pulsing nature of the system can upset the vehicle's balance (think teetering on 3 wheels). In this case a true locker is advantageous.
 
m85476585 said:
I don't know about the 5th gen. But I know they made the rear differential stronger, so I wouldn't worry about the reliability of an e-locker if it has one as an option.
Click to expand...
The 5th gen elocker is stronger than the one in the 09 TE, 05-15 Tacomas, and <2010 FJC. Downside is a lack of aftermarket gear options. Until a couple years ago, it was only expensive 3.73 or 4.56 Toyota gears (4.56 came in the rare as hen's teeth 4cyl 5th gen that was only available a couple of years), then 4.56 Nitro, and very recently 4.88 Nitro.

The elocker is not as fast to engage as I would like and for that reason alone, I would have replaced it with an ARB when I re-geared, if that were possible. My front ARB locker locks and unlocks almost instantly when it isn't under stress. The elocker can take a hundred feet or rolling back and forth turning the wheel to engage sometimes.
 
ARunner said:
The biggest gripe I have with ATRAC on our 4runners (I understand FJs may be a little more aggressive in engagement) is that you need some wheel spin to engage the functionality. When you're in a precarious position, wheel spin is not something you necessarily want. That combined with the pulsing nature of the system can upset the vehicle's balance (think teetering on 3 wheels). In this case a true locker is advantageous.
Click to expand...

Does any 4Runner model have a locking front diff? I dont think so, and I wonder why not.
 
ProspectiveBuyer said:
Does any 4Runner model have a locking front diff? I dont think so, and I wonder why not.
Click to expand...

Front lockers can often get you in trouble on off camber or slippery (icy) surfaces if you don't know what you are doing. This is why Toyota hasn't offered a factory front locker on any vehicle since the 90's Land Cruiser. ATRAC is also a helluva lot cheaper and being a passive software system is a lot more user friendly to the 99% of owners who have no clue how their system works in the first place. I can say with conviction while there are certainly circumstances where a front locker is superior to ATRAC, a rear locker combined with ATRAC like that found in my truck / FJ's / Tacoma's is a formidable combination especially for a daily driver. Keep in mind also that even the venerable Wrangler is pretty worthless in any trim package other than the Rubicon because it has open diffs front and rear with no traction control help at all.
 
In addition to the reasons above, it is easy to break IFS parts with a locker, if you don't know what you are doing.
 
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