a-trac 101 (2 Viewers)

2000UZJ

Where's My Hammer?
Joined
Oct 7, 2008
Messages
8,871
Location
Earth
100 Series A-TRAC 101

I wrote this mainly to help those who are not familiar with A-TRAC. I have been wheeling for 6 years total. I realize that to some of you this is chump change. I grew up in the years of ABS, traction control, and all that wonderful technology. So what does this mean? I may not be the most experienced wheeler across the board, but wheeling the same vehicle for 6 years, 2 times a month will make you understand every aspect of the vehicle, and how to push it further with control, safety, and keeping all the parts turning nicely. When it comes to wheeling a vehicle equipped with A-TRAC, it's not about the books, not always about the facts. You can watch a 100 wheel anywhere and get a good understanding about A-TRAC. “Information is not knowledge” (Einstein). Being behind the wheel of a 100 with A-TRAC has given me more than knowledge. When I wheel, the 100 becomes a part of me (cheesy, huh?). If you follow and understand my personal brochure I have prepared for the 100 Series guys, you will quickly develop the ability to take the 100 further than you ever thought possible.

DISCLAIMER: I take no responsibility if you damage your vehicle off road.

What is written below is from my brain and a single post I have used for technical data. I did no research on A-TRAC, other than what I already know about the system and my personal experience.
____________________________________________________________________


100 Series Active Traction Control 101
-What is A-TRAC?
Most of us that drive our 100 Series off the paved roadways know that there are two types of 100 Series (UZJ-100 N.A Spec) traction systems, one is mechanical and one is electrical. When the 100 Series was released in 1998 it came with a factory locker in the rear differential, a locking center differential, and a open front differential. Toyota redesigned the 100 Series differential and traction control system in 2000. Starting in 2000 Toyota removed the rear locker, and redesigned the front differential to withstand more stress. They added a system known to us as A-TRAC. From 2000-2007 IFS 100's were equipped with A-TRAC. Despite the revisions the system went through for newer vehicles (FJ, Tacoma, etc) the 100 Series A-TRAC system was never updated. Through the first 7 year run of A-TRAC equipped 100's, all came with first generation software. First generation A-TRAC uses a single speed sensor on each wheel and can only monitor and effect 2 wheels at any given time (within a certain throttle range). The updated versions were equipped with the ability to monitor wheel speed on 3 wheels at a much faster rate, thereby making it smoother, more predictable, and easier to maintain optimal performance.

"If a tire slips while the vehicle is being driven off-road, the function of the differential gear causes a large amount of drive force to be applied to the tire that is slipping. The A-TRAC function helps restrain the slippage by controlling the engine output and brake fluid pressure that is applied to the slipping wheel and distributes the drive force that would have been lost in the slippage, to the remaining wheels. It independently controls the brake hydraulic pressure to all four wheels in accordance with the extent of slippage detected by the skid control (ECU).

Based on the vehicle speed that has been calculated from the speeds of the wheels and the deceleration sensor, the skid control ECU computes the target control speed in accordance with the transfer case range. The ECU compares the target control speed and the speeds of the wheels to determine whether or not a slippage exists. Upon detecting a slippage, the ECU controls the solenoid valve of the brake actuator to control the brake fluid pressure that is applied to the slipping wheel. When the wheel speed becomes lower than the target control speed, the ECU stops controlling the brake fluid pressure. The target control speed and the brake fluid pressure control vary in accordance with the transfer case range:

H = gradual fluid control pressure
L = sudden fluid control pressure
L + first gear = fluid pressure control only on the front wheels (downhill slippage control)"

(Comment about L+first gear-It does monitor rear wheels, the fluid pressure is very high and aggressive a-trac intervention)
(Source: IH8MUD Member "Sandroad", quoting from a Toyota Manual [3-31-2011])





--How do I know if it's working?
The suspension in the 100 Series is limited in front wheel travel and total articulation (as we all know). If the system is working, you will feel it as feed back through the brake pedal. Also, the ABS unit under the hood will be "clicking / clunking" and the A-TRAC light will flash on your instrument panel. The system works the brakes and ABS unit overtime, it DOES have a time limit, it WILL shutoff, and you WILL loose any aids assisting you while off-camber. . A-TRAC is limited to 8-13 seconds of constant operation. After that the system will sound beeps (3 seconds to shutting down) and you will need to wait for the system to cool down.

What is the best approach to an obstacle with A-TRAC?
When you approach something, lock the center differential (flat, uphill obstacles. Leave unlocked/open for downhill obstacles). Always enter a climb you cannot clear with no bumper contact at a slight angle. Turn into the obstacle keeping the wheels within a imaginary 35* boundary. When A-TRAC starts to work and pull you up, straighten out. If you lift a wheel in the front you will feel feedback through the steering wheel, brake panel, and floorboard. Keep the wheel straight until you must turn, making small adjustments with minimal steering input. High range provides a less aggressive A-TRAC operation, use in flat, open, slick areas where lots of wheel spin is necessary, keeping the 100 in high range will not allow A-TRAC to intervene with high pressure, locking the CDL will shut off VSC letting you slide and maneuver with minimal electronic intervention. Low range will boost the fluid pressure in the system making A-TRAC bite quicker. Also, when A-TRAC operates at a high pressure state, it will and can suddenly and violently stop the wheel if you loose traction at a slow speed and the system sends fluid to that wheel. BE cautious as you can damage drive line components. You need to know your vehicles limits, and how A-TRAC will intervenes and reacts to your input.


Here is an example of A-TRAC's (1 generation software) lag time between traction loss, no throttle/brake input. Tip: When you enter a V ditch and the front end rises, left foot brake until you need traction. With no throttle input A-TRAC will not activate, resulting in a "run-away-tire". It will spin at idle speed until it senses you have pressed the gas and want to continue forward, like the video shows. I did not left foot break and let the wheel spin freely, when A-TRAC sensed throttle input it stopped the wheel instantly, this is what will blow your front differential due to deflection on shock loads



Another example the high pressure operation behavior (note how the wheels never turn further than needed). Keep the throttle steady, no sudden throttle changes, straighten up as soon as possible

Another video shows a climb that overheats the system and causes 2 things, a alarm sounding, and a system shutdown. You can hear the alarm towards the end of the climb, it will not stop sounding until the system is ready to go again. When this happens, get off the gas, stop as quickly as possible so prevent rapid wheel spin and forward momentum loss. If you stay on the gas and loose A-TRAC, the 100 will revert to a open/open vehicle, allowing tires to spin freely possibly a blown drive line component when the spinning wheel hits traction again. DO NOT BOUNCE THE FRONT END OF A 100 SERIES. Wheel hop on the front end can be fatal for the CV and/or front differential. This applies for just about any vehicle...


Here is a excellent video of A-TRAC at work, constant throttle, wheel straight, and no adjustments once the system starts working, minimizing the condition changes and allowing A-TRAC to focus on one thing. Getting you up and over.



Tips​

So after 6 years of wheeling in the muddiest part of the southeast, everything from rock gardens, steep climbs, ledges (rock, dirt, whatever), deep mud, ice and snow. I have learned many valuable tips that make my truck go places I take it, I have wheeled with locked Jeeps, 4Runners, FJ's, 80's and anything you can think of, A-TRAC has never let me down. I wheel hard, I wheel safe and smart. To much throttle and you go nowhere but to the repair shop. Not enough throttle and you don't go anywhere and people get mad that you can't figure out your trucks traction system. The right amount of both is required, there is a fine line with A-TRAC. I'll start with the most important part...

Throttle- Don't go about your way like Jeremy Clarkson does... POWAAA!!! is not the answer with A-TRAC. It's the opposite. "POWAAAA" will result in nothing other than broken parts, looking like a complete idiot, and probably flip your truck. If you want to prove me wrong, give it a shot :)
When it comes to throttle input, 1,200RPM-2,200RPM is the sweet spot. You may go above that but make sure your tires with traction are maintaining traction so the system can work properly. When you start spinning tires that are on the ground, you have to much throttle and the system will simply turn off. In low range you should not need to go above 2,200 RPM while climbing something off-camber that requires A-TRAC. Plenty of torque and speed at 2,200RPM. Always lock the center differential, when you climb an obstacle with an A-TRAC equipped 100. Turning sharply while off-road/off-camber will not damage the CDL, but keep it open if you do not need the 50/50 split, or may need VSC. As stated by Lexi4darin, using the 2nd start feature in low range forces the transmission into 2nd gear. You will have a similar throttle response to high range while in this mode. I do not use it mainly due to the amount of torque it reduces while climbing. On slippery climbs, where wheel spin is not needed/wanted, use 2ND start and leave the shifter in "D".

Edit: Also, please make your your center diff lock has fully engaged before you commit to a climb/off camber situation. Attempting to lock the CDL while off-camber or during wheel spin will result in a loud grinding sound, which is the sound of gears tearing themselves apart (don't ask how I found this out). This is not good, if you enter a situation and forgot to lock the center differential and you are in a tight situation and cannot back up or adjust: Press brake pedal firmly, place vehicle in neutral and lock the CDL, let the vehicle roll back very slowly until you hear the actuator motor cycle completely. Do not rely on the dash lights, rely on hearing in this situation. If you are able to back out or adjust your line, begin to adjust your line. When all 4 wheels are on the ground you may press the CDL button. Putting the transmission in neutral relieves any binding between the F/R axles and allows to lock up much quicker.

When you are ready to unlock the center differential don't just push the button. The actuator can sense the amount of pressure that is on it, but that won't necessarily keep it from unlocking the center differential in a tight bind. It won't hurt to drive with the CDL locked on a tight trail, just make sure you are free of binding before unlocking. A nice quite, smooth unlock should occur. If you cannot unlock the CDL, drive in reverse while turning the steering wheel. This will undo any forward binding you have built up.

Example of to much throttle:

Steering- I have found that A-TRAC operates best when the front wheels are straight. Certain situations require you to turn, if you can manage to keep forward momentum try to keep the wheels straight, turn only when needed and return when you are done. Never start with the wheel cranked and give it more gas if you don't start moving up your obstacle. If you MUST turn full lock and you know A-TRAC will kick in. Begin the climb with the front wheels as straight as possible then turn in full lock, getting that forward momentum is key for a full lock climb while using A-TRAC. Remember to straighten out as soon as you can.

Overheating and shutdown- the system shuts down to prevent the brakes and ABS unit from overheating. To keep it from overheating let off the gas and let your forward momentum carry you (if possible). Use the brake as much as possible (some argue it shuts off A-TRAC, which it does). If A-TRAC can get you up and over the initial climb, most likely a little left foot braking can keep momentum going. This will allow the system to cool down for a few seconds. To transfer the power delivery method from "left-foot braking" to A-TRAC let off the gas as you release the brake( reducing wheel speed with reducing throttle, releasing the brake to enable A-TRAC), immediately return on the gas to return to A-TRAC operation (smooth throttle input, sudden input will cause a violent A-TRAC intervention due to a spinning wheel). When the system shuts down I come to a complete stop, put the vehicle in neutral. I cannot find any proof of this... so I am open to comments and opinions. I have found that when A-TRAC shuts down, putting it into N and rolling back 6" tricks the system and allows it to start up with no cooling period. I do not know how hot the system gets, but I have repeated this method on very long climbs with no ill-effects on the system or brakes.

I'd like to finish this with a few clips showing A-TRAC working in some pretty tough spots.


Happy wheeling :beer:
 
Last edited:
Joined
Feb 10, 2005
Messages
4,626
Location
in the nappy dugout
yes wicked nice right up. I use to have a 98 with a center and rear locker and recently moved to a 03 with A-trac. I was always skeptical of the A-trac but when you finally learn how to use it it works awesome.
 

e9999

Gotta get outta here...
Moderator
Joined
Sep 20, 2003
Messages
17,818
Location
US
Interesting thread, thanks for taking the time. Looking forward to a good discussion and may add to FAQ.
 
Joined
Nov 8, 2004
Messages
263
Location
Pittsburgh, PA
Great write-up. I love my atrac equipped 100, and am able to keep up with (and sometimes out perform) the locked jeeps, pickups, etc like you mentioned.

Great vids too.
Cheers.

Sent from my Thunderbonner using IH8MUD
 
Joined
Jul 23, 2010
Messages
2,516
Location
Hampstead, NC
Here is my A-Trac question, and maybe nothing would have helped.

My one stuck that really frustrated me happened on my buddy's farm searching for turkeys. The spot was compact, yet wet, red clay. My MTs spun on top of it like ice, and would not dig in. It was a pretty good up hill left turn that leaned to the right at 10-15 degrees. I hit it at about 15 mph and came to a stop. First, i did the straight line low rpm atrac friendly dive. This slowly slid me closer to a tree on the black right and down the hill. After a few attempts with atrac to no avail, i figured lets just open the throttle and lit the tires clean themselves an hopefully grab. WOT took me about a foot forward and then slipped to a stop. Finally, i threw my maxtrax down and pulled right out. Atrac has been awesome on rocks, pulling wheelies etc, but this was the first time i was pretty frustrated. Yes it was really slick clay, but is there something i could have done better to pull myself out of it.

On a side note, i love A-trac. My previous rig was locked in the reare with a chirpy limited slip up front, and other than mud, the a-trac is far superior.

Bottom line, what should i have don differently to help it work in what looked like not to bad of a situation compared to what i have seen a-trac do before?
 

2000UZJ

Where's My Hammer?
Joined
Oct 7, 2008
Messages
8,871
Location
Earth
Here is my A-Trac question, and maybe nothing would have helped.

My one stuck that really frustrated me happened on my buddy's farm searching for turkeys. The spot was compact, yet wet, red clay. My MTs spun on top of it like ice, and would not dig in. It was a pretty good up hill left turn that leaned to the right at 10-15 degrees. I hit it at about 15 mph and came to a stop. First, i did the straight line low rpm atrac friendly dive. This slowly slid me closer to a tree on the black right and down the hill. After a few attempts with atrac to no avail, i figured lets just open the throttle and lit the tires clean themselves an hopefully grab. WOT took me about a foot forward and then slipped to a stop. Finally, i threw my maxtrax down and pulled right out. Atrac has been awesome on rocks, pulling wheelies etc, but this was the first time i was pretty frustrated. Yes it was really slick clay, but is there something i could have done better to pull myself out of it.

On a side note, i love A-trac. My previous rig was locked in the reare with a chirpy limited slip up front, and other than mud, the a-trac is far superior.

Bottom line, what should i have don differently to help it work in what looked like not to bad of a situation compared to what i have seen a-trac do before?

Since the system can only control two wheels at a time, a slick hill climb can only be conquered if you air down, a-trac can be defeated easily in the right conditions. Mud is one of those conditions, even with all my knowledge about a-trac...mud is the biggest problem this is my approach to a muddy hill climb where a slow and reasonable get thrown out the window...

 
Joined
Jul 23, 2010
Messages
2,516
Location
Hampstead, NC
i gotcha, throttle down, and hope for the best. Momentum goes a long way!! Just didnt know if i were missing a subtlety or a-trac trick.
 
Joined
Dec 26, 2009
Messages
862
Location
Bay Area, CA
Bottom line, what should i have don differently to help it work in what looked like not to bad of a situation compared to what i have seen a-trac do before?

Yukon, sometimes slow and steady is the best route. I might have tried a 2nd gear start to "maybe" gain a few feet of travel at a lower torque. With the 2nd gear start, maybe the tires would have been less likely to slip since there's less torque available at lower speeds.

Interesting marketing factoid: the 2nd gear start in the LX/LC is called "Snow" in the sedan line of Lexus models. The idea is, once engaged, the driver can go from a stop to a rolling start in snow. It's supposed to help tremendously in snow/icy conditions even on a hill start by preventing the slippage to begin with.
 

2000UZJ

Where's My Hammer?
Joined
Oct 7, 2008
Messages
8,871
Location
Earth
Yukon, sometimes slow and steady is the best route. I might have tried a 2nd gear start to "maybe" gain a few feet of travel at a lower torque. With the 2nd gear start, maybe the tires would have been less likely to slip since there's less torque available at lower speeds.

Interesting marketing factoid: the 2nd gear start in the LX/LC is called "Snow" in the sedan line of Lexus models. The idea is, once engaged, the driver can go from a stop to a rolling start in snow. It's supposed to help tremendously in snow/icy conditions even on a hill start by preventing the slippage to begin with.

Added that to my post. I didn't even think about the 2nd start in low range. However it would probably reduce the effectiveness of a-trac, since you will have to apply quite a bit more throttle to pull yourself over. I will have to play with this next time I go out.

In a situation where you need minimal a-trac I think 2nd start would be much smoother. Especially for passengers and keeping the jumpy-ness to a minimal.
 

Copenhagen1

1000+ Club
SILVER Star
Joined
Feb 9, 2006
Messages
1,273
Location
East Texas
Damn nice thread! I have owned my 2001 for over a year now and never knew it had that kind of prowess:cool:.

I always thought atrac was some sort of electronic babysitter system to bail soccer moms out of power slides:eek:

I have to give a big thanks to you for writing this thread. It will change my whole approach if I ever do take mine down more than ranch roads.
 
Joined
Dec 26, 2009
Messages
862
Location
Bay Area, CA
Added that to my post. I didn't even think about the 2nd start in low range. However it would probably reduce the effectiveness of a-trac, since you will have to apply quite a bit more throttle to pull yourself over. I will have to play with this next time I go out.

I imagine it would reduce the a-trac intervention but that could be a good thing too. I think of A-trac as intervening when the vehicle is slipping. I think of a 2nd gear start as a way to maybe prolong traction or delay when slipping will occur. Going up a snowy, er, e-hem a muddy hill, 2nd start could have enough power to carry the vehicle but not enough torque to slip the tires. Depending on the situation.
 
Joined
Nov 20, 2008
Messages
561
Location
Reno, NV
I always thought atrac was some sort of electronic babysitter system to bail soccer moms out of power slides:eek:

No thats what VSC is. For soccer moms, ATRAC is what gets them up onto the mall sidewalk.

Great write up, the vids help alot, I actually learned the most about ATRAC initially when you posted a few vids about 2 years ago, worth a million words :cheers:
 

Nottajeep

Enemies of the State
SILVER Star
Joined
Aug 17, 2008
Messages
3,342
Location
BFE
So it seems Atrac is better than open diff, but not as good as front and rear lockers? Probably a can of worms, but that is my take after watching your vids. Excellent thread, btw.
 

2000UZJ

Where's My Hammer?
Joined
Oct 7, 2008
Messages
8,871
Location
Earth
So it seems Atrac is better than open diff, but not as good as front and rear lockers? Probably a can of worms, but that is my take after watching your vids. Excellent thread, btw.

Lockers are always better in off-camber situations. a-trac is better in a tight, narrow trails. There is a place for both when the time comes.
 

Users who are viewing this thread

Top Bottom