Making sense of TRAC, Auto LSD, ATRAC, VSC, & Rear Diff lock. - Page 8 - Toyota FJ Cruiser Forum
Transmissions / Transfer Cases / Traction Aids This area is for discussion, questions and problems with the FJ Cruiser's gear train, including topics on A-TRAC, VSC, locking diffs, gear ratios, manual vs. AT, etc.

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post #71 of 166 (permalink) Old 12-04-2006, 01:22 AM Thread Starter
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Re: Making sense of TRAC, Auto LSD, ATRAC, VSC, & Rear Diff lock.

Wow! I just reread this thread and relearned some things. A BIG thanks to Thai, KLD, and others for helping to clarify these electronic doo-dads we have on our FJ's.

Just a quick review of what was originally posted plus notes from KLD, Thai, CruiserLarry, & Others.

Trac : Traction control. All FJ's have this, both 2WD & 4WD. Works automatically when ignition is started (no push button needed). Works by applying brakes and controls (decreases) engine throttle to give added traction to varying wheels when system detects wheel slippage/spinning ("think spinning your wheels on ice"). Works all the time in 2WD and in 2H & 4H (AT) or HL (MT). This system basically helps to maintain traction in slippery conditions such as wet/icy for forward movement by applying brakes and controlling engine throttle to regain/maintain traction as a safety feature.
TRAC is disabled in 4LO. Again, you don't want this system to control engine power when you are climbing obstacles.

ATRAC : More aggressive form of TRAC & for 4WD OFF ROAD use only. Does the same thing as TRAC except it doesn't cut/control engine throttle. Instead, it transfers torque from slipping/spinning wheel(s) to non slipping wheel. This gives added traction & forward momentum to overcome Off-road obstacles. This can only be engaged while in 4LO (AT) or LL (MT) and by pressing the "ATRAC" switch.
Also, only 4WD models with the Rear Diff Locker have ATRAC capability. Even then, you need the $50 ATRAC switch installed to use this system if you didn't purchase either Upgrade Pkgs with your FJ (UP or UR).
*AT: to go into 4Lo, stop, put into Nuetral, then shift into 4Lo (short knob).
MT: refer to manual, sorry I have the AT.

Auto LSD: found on 2WD models. Similar to ATRAC for 4WD. Must press the Auto LSD button/switch to activate it.

VSC (vehicle stability control) : integrates ABS, TRACtion control, engine control, etc to prevent the vehicle from skidding when cornering. Prevents oversteering or understeering & will save your ass if your car loses control (Thai). Detects angular momentum and tries to control direction of skid. VSC is automatically activated when the FJ reachs 9mph or 15km/h.
*VSC automatically turns itself off (VSC off light on dash comes on) when 4H/HL or 4Lo/LL is activated (AT/MT) or when the Rear Diff is locked. VSC is for preventing rollovers at high speeds thus not used while wheelin' in 4Lo/4H.


Rear Diff Locker
: Not all 4WD models come with this. Switch/button activated. You must be in 4Lo or LL. It locks the rear axle so that it acts as one rod. If one wheel turns, so must the other so that not all power/torque is lost to the spinning wheel. Diff b/t Rear Locker and ATRAC is that with
Rear Diff Locker, both rear wheels spin in unison and steering tends to be rather difficult (so be careful near small ledges, ruts, drop offs). ATRAC, rear wheels are not locked and steering is not comprimised so you have more control of the vehicle. Apparently one works better than the other for certain situations while wheelin or you can do the Atrac-Locker Hack and have the best of Both worlds.

So at relatively high speeds TRAC will slow you down & aid in traction control in slippery situations, while VSC will give your more control during turns, skids, and saving your ass (roll over prevention).

While ATRAC and Rear Diff Locker is specifically for use in 4LO. While either of these are engaged, the TRAC and VSC is turned off. This makes sense, b/c they are safety systems to slow you down when you're going to fast, while ATRAC and RDL will aid to move you forward when you're going too slow or stuck.

Other Recommendations: Not necessary to be in 4H when it's raining or lightly snowing in the city, since this will deactivate VSC. VSC is what will save your ass at high speeds (per Thai). If you stay in 2H, you have TRAC and VSC to make necessary corrections if you slip & slide. If you do choose to put it in 4H for these situations, at least you still have TRAC working for you. But again, Thai says TRAC is turned off after 40+ mph or so. Many here feel you shouldn't be going fast (>40mph) while in 4H. 4H is probably more appropriate if you encounter thick/compacted snow or icey roads as FJJack mentions. You can quickly find out which is better with a test this winter. Try 2H and 4H and make up your own mind.

4H and 4L should generally be reserved for off roading use. 4H for light trails (gravel/dirt roads) and 4Lo for mod-large rutts/rocks. Obviously if a meteorite hits your town and all hell breaks loose then by all means put her in 4H/4Lo as needed.

Again, A great big thanks to KLD, Thai, CruiserLarry, RoverGGM, Alex, and countless others for their technical expertise on this forum.

Even a blind squirrel finds a nut every now and then.

Last edited by Tranman; 12-04-2006 at 10:57 PM.
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post #72 of 166 (permalink) Old 12-07-2006, 08:31 AM
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Re: Making sense of TRAC, Auto LSD, ATRAC, VSC, & Rear Diff lock.

WAIT, Tranman, don't go yet! KLD has stated twice now that TRAC does not control the engine throttle in 4h on the AT. This is the single most important point for me. Since AT transmission folks do not have the "AWD" of the MT, 4h is all we got for low traction, but faster-than-4wheel-offroad travel.

As I see it now, if you are driving around in 2wd when it is slippery out and you accelerate into a turn you might fishtail a bit but the VSC will correct it for you. (What if you also instinctively try to counter steer - will it correct for your correction?) If you did the same thing in 4h, you'd be less likely to skid in the first place and the TRAC system would actively distribute traction if you (the wheels) did slip by using the brakes but nixes the down toggling of the throttle that vsc uses. Which drive system is easier to control may depend on whether folks have had experience driving with cars that were typically rear wheel drive with no ABS or anything else electronic - in that case they may feel safer in a vehicle that they can "feel" the limits of traction. I use to think this until I drove around in a ford van in the snow. Would have killed for traction controls of any kind.

Anyway, one thing I use to like my jeep laredo for was that i could put it into 4 wd full time and if i had to pull out into traffic quickly I could always count on the jeep to pull me out quickly with no wheel slippage. It actually couldn't accelerate fast enough to slip both the front and the back wheel. In the FJ, 2 wd with all the electronic du dads makes me feel a bit nervous when I do this because TRAC is cutting the engine speed and not just sending torque to another wheel. It actually feels like my fj is crippled. It usually figures it out and gets me going but I shake my head every time thinking "there has to be another way". And yes, I should probably drive my fj not like a sports car but hey I really like going when and where and as fast from the line as I want - whatever i drive (my financee hates it).

Alright so if i am understanding KLD correctly if I accelerate from a dead stop and it happens to be slippery, I would not experience the throttle drop only a brake to the slipping wheel that would tend to transfer torque elsewhere - to the wheels that have grip. Net result, I would accelerate faster than when in 2wd. This would also be quite useful if going up hill in the snow. All the torque would be available at one wheel or another and the engine would not be cut off. I keep having visions of my FJ refusing to go forward because each wheel slips too much thereby cutting all engine power and me.. stranded... alone...

But now that I know TRAC doesn't cut power to the engine in 4 h AT - I'll never be stranded on a hill in the snow.

Many thanks to all those contributing to this thread.

Last edited by FJconvert?; 12-07-2006 at 08:36 AM.
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post #73 of 166 (permalink) Old 12-07-2006, 08:51 AM
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Re: Making sense of TRAC, Auto LSD, ATRAC, VSC, & Rear Diff lock.

Ow! My brain is full!

"Wild" Bill Wheeler



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post #74 of 166 (permalink) Old 01-04-2007, 11:28 AM
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Re: Making sense of TRAC, Auto LSD, ATRAC, VSC, & Rear Diff lock.

Nice review. Question. I have to get the automatic, it servews as the Wife's second car. I am not thrilled with part time 4wd and am waiting for full time 4wd to be maited to the automatic. Any thoughts or reasons why they dod this? Thanks, Jack Stein jstein@sunocoinc.com
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post #75 of 166 (permalink) Old 01-05-2007, 12:43 PM
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Smile Re: Making sense of TRAC, Auto LSD, ATRAC, VSC, & Rear Diff lock.

Quote:
HUDsFJ previously said: View Post
Toyota.com : Vehicles : FJ Cruiser : Bulletin

Check out this link to the FJ bulletin. I think this will answer everyone's questions. It says in Section 1: Engineering. Traction tools. that the ATRAC not only applies brake to the slipping wheel, but transfers the power through "the open differentials to the wheels getting traction." This is more than just a brake to the wheel that is not getting traction but gives added power to the wheels getting traction.
MO
Stupid question??? If you stop one wheel from moving were is the power going to go but to the other wheels. It seem like this aspect of the system is not an added "feature" but just a fact of power distribution. In a generic system the power goes to the wheel with least resistance. Braking one wheel just takes advantage of this (Traction Control). Only locking diff will give you even distribution.

Of course I may be totay wrong on this, it has happened before.
Tomas
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post #76 of 166 (permalink) Old 01-05-2007, 12:50 PM
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Re: Making sense of TRAC, Auto LSD, ATRAC, VSC, & Rear Diff lock.

Quote:
tdawson previously said: View Post
Stupid question??? If you stop one wheel from moving were is the power going to go but to the other wheels. It seem like this aspect of the system is not an added "feature" but just a fact of power distribution. In a generic system the power goes to the wheel with least resistance. Braking one wheel just takes advantage of this (Traction Control). Only locking diff will give you even distribution.

Of course I may be totay wrong on this, it has happened before.
Tomas
You are correct, that is the mechanism by which it accomplishes the power transfer to the wheel that has better grip.
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post #77 of 166 (permalink) Old 01-14-2007, 12:06 PM
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Re: Making sense of TRAC, Auto LSD, ATRAC, VSC, & Rear Diff lock.

Awesome review,very informative,better than the owner's manual.
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post #78 of 166 (permalink) Old 01-18-2007, 08:36 PM
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Re: Making sense of TRAC, Auto LSD, ATRAC, VSC, & Rear Diff lock.

Quote:
wadecc04fj previously said: View Post
Awesome review,very informative,better than the owner's manual.
X2

Mike
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post #79 of 166 (permalink) Old 01-18-2007, 08:58 PM
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Re: Making sense of TRAC, Auto LSD, ATRAC, VSC, & Rear Diff lock.

Quote:
tdawson previously said: View Post
Stupid question??? If you stop one wheel from moving were is the power going to go but to the other wheels. It seem like this aspect of the system is not an added "feature" but just a fact of power distribution. In a generic system the power goes to the wheel with least resistance. Braking one wheel just takes advantage of this (Traction Control). Only locking diff will give you even distribution.

Of course I may be totay wrong on this, it has happened before.
Tomas
You're right. Here is a post i wrote a while ago on this very topic: Toyota - 4Runner . org Forum - How does ATRAC work??

Hope this helps.
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post #80 of 166 (permalink) Old 01-18-2007, 09:20 PM
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Re: Making sense of TRAC, Auto LSD, ATRAC, VSC, & Rear Diff lock.

Quote:
FJconvert? previously said: View Post
As I see it now, if you are driving around in 2wd when it is slippery out and you accelerate into a turn you might fishtail a bit but the VSC will correct it for you. (What if you also instinctively try to counter steer - will it correct for your correction?)

If you did the same thing in 4h, you'd be less likely to skid in the first place and the TRAC system would actively distribute traction if you (the wheels) did slip by using the brakes but nixes the down toggling of the throttle that vsc uses.

In the FJ, 2 wd with all the electronic du dads makes me feel a bit nervous when I do this because TRAC is cutting the engine speed and not just sending torque to another wheel. It actually feels like my fj is crippled.

Alright so if i am understanding KLD correctly if I accelerate from a dead stop and it happens to be slippery, I would not experience the throttle drop only a brake to the slipping wheel that would tend to transfer torque elsewhere - to the wheels that have grip. Net result, I would accelerate faster than when in 2wd.

I keep having visions of my FJ refusing to go forward because each wheel slips too much thereby cutting all engine power and me.. stranded... alone...
I will try and answer some questions according to the paragraph in the above quote.

When driving a vehicle with VSC, you should NOT try to countersteer or do any wheelsawing to correct your mishap. Like driving with ABS, we all need to retrain the way we drive. With VSC, you must ALWAYS point your steering wheel in the direction that YOU WANT TO GO. Keep pointing it...don't countersteer out of a fishtail. If you do countersteer a bit (out of habit), then it will still be OK because VSC is pretty aggressive when you're in trouble. If you guys have experience VSC at full tilt (when you're in deep trouble), then you will know that VSC cuts throttle aggressively, thus slowing you down immediately to help you get under control while braking (simultaneously) the appropriate wheel(s) to avoid spinning. Here is a good video of how VSC works: Toyota - 4Runner . org Forum - Vsc

Although the old 4x4 boys will tell you to put your FJ in 4-HI (in AT models) when raining, this is not a good idea. For one, you can still bind if you turn sharp on a rainy street (not enough slippage)...puts more stress on your transfer case (not much, but why risk it, right?). Another reason is that you will forget that you're in 4HI down the road when you get off the highway and turn a corner. Stick with VSC...it works much better at highway speed than 4HI. And in snow or ice, stick with VSC (all-speed) and TRAC (at low speed).

Yes, VSC (and TRAC) does have a weakness...like the one you described when you try to merge onto on-coming traffic from a stop. But, like ABS, this is something you need to learn and adapt to. Nothing in life is perfect.

I do believe that VSC and TRAC are very closely related and interconnected at the chip level. Therefore, if the road is really wet/slick and you accelerate aggressively from a stop and spin your rear tires a lot, then you WILL experience DE-throttling. Therefore, you may get stuck in snow, which has happen to plenty of 4runners. If you are anticipating a severe snow storm overnight, then you may want to put your FJ into 4HI before going to sleep. This will allow you to power out of being buried under snow without VSC/TRAC interfering.
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