turn off traction control?

[dcampen]

LOCKING the center differential LOCKS the torque bias, 50% to the front axle, 50% to the rear.

This is what an open differential does - always distributes the torque equally. So what you are saying here is that when I lock the Torsen center differential on my 4Runner I convert it into an open differential. That would be a useless thing to do.

 

[ToolmanJohn]

Here. I'm done.

Either everyone is wrong, or you are right. sigh.... even Toyota says it's so.

http://www.toyota-4runner.org/showthread.php?s=&threadid=12

 

[dcampen]

Either everyone is wrong, or you are right. sigh.... even Toyota says it's so.

Well, you don't seem to understand. Where does Toyota contradict my statements? The link you posted was by Thai and this portion (about the 50/50 power split) is indeed inaccurate or at least very misleading:

"To LOCK the center differential (thus, TRUE 50/50 power split between front and rear axle), you need to push the button to the left of the steering wheel on dash. This should be done only on loose terrain (because of 50/50 split) to prevent binding of the center differential. Again, this will disable the VSC, allowing you to power through mud (which you cannot do effectively if VSC is ON)."

Yes, if none of the wheels are slipping then the locked differential will split the power 50/50 front to back but if, as in the example that I have given twice before, the front wheels were on a frictionless surface then all power would go to the rear wheels.

Perhaps you are getting confused by some of the descriptions of the Torsen differential where they use the term "locking" to describe the mechanical action inside the differential that changes the power distribution ratio when one set of wheels starts to slip. In this vein you will somtimes see the Torsen described as an "automatically locking differential" but this locking is as I just described in this paragraph and is not the locking you get when you push the "lock" button inside the truck.

Again, it is an open differential that produces a 50/50 torque split under all circumstances. A locked differential will send all power to whatever is not slipping.

 

[kglueck]

:dunno:

ever see the Far Side where the kid raises his hand during class and tells the teacher, "May I be excused, my brain's full..."? Right now, I'm that kid... :

 

[dcampen]

Here is a good description of an open differential:
http://auto.howstuffworks.com/differential6.htm
Notice how on this and the next page they repeatedly emphasize:
"Remember that the open differential always applies the same torque to both wheels"

And then they have a good description of a locking differential:
http://auto.howstuffworks.com/differential10.htm
"The locking differential is useful for serious off-road vehicles. This type of differential has the same parts as an open differential, but adds an electric, pneumatic or hydraulic mechanism to lock the two output pinions together. This mechanism is usually activated manually by switch, and when activated, both wheels will spin at the same speed. If one wheel ends up off the ground, the other wheel won't know or care. Both wheels will continue to spin at the same speed as if nothing had changed. "

The center differential in the 4Gen 4Runners is a limited slip differential when it is unlocked but when it is locked it behaves exactly the same as a locked open differential.

 

[Thai]

BOTH of you are right...depending on the traction surface...please read my post again in that link for this one exception...where both wheels on either axle are on ice. If that is the case, then Torsen is at it's weakest...it will send power to the axle with the least traction (up to 100% in theory). However, anything short of complete frictionless surface, Torsen is good. Thus, in off-roading over severe terrain, it is advisable to lock the center diff to prevent this from happening (however rare that may be). Of course, locking this will also shut off VSC. Remember, ATRAC is STILL active on 4wd models, no matter what you do!

 

[Thai]

Here is my attempt to claify

Dcampen, you're getting into an area that not many people (including magazine editors) understand. But, you are right. When you truly lock a differential, you have 100% of power to either end.

For example, on the Mercedes G500 (3 lockers: front, center, & rear), if you lock all of it's lockers, then 100% of power is available to ANY single wheel. Thus, if you have three wheel spinning on ice, then the G500 still can move forward because that single wheel has 100% of power (not 25%). Why?

Well, the power flow from the engine to the center diff. So, the center diff has 100% of power. Now, the center diff sends power to the front and rear axles...but remember, since it is lock, the front and rear axles are locked together...what one end gets, the other end also gets...so, if one end gets 100% of engine power, the other end does also! Now, let's focus on the front axle. The front axle gets 100% of engine power. Now, since the left and right front wheels are lock together, what the left wheel gets, the right also gets because they are locked together. (Think of a simple stick with two wheels superglue together on either end...if you turn the left wheel, then the right wheel will also turn too.) So, so far, each front wheel gets 100% of power. The same explanation applies to the rear axle.

Therefore, because the center diff, front axle, and rear axle are locked together, they behave as one. So, if one end turns, the other end must also too........100% of engine power to each wheel.

 

[Vortec4800]

Re: Here is my attempt to claify

Therefore, because the center diff, front axle, and rear axle are locked together, they behave as one. So, if one end turns, the other end must also too........100% of engine power to each wheel.

Thai is right on the money. Essentially locking our center diff is more of a 100/100 split than a 50/50 split. So, dcampen, while you are correct, 100% of the power DOES go to the front wheels if they are on a frictionless surface, 100% of the power still goes to the real wheels also. Just remember - if your center diff is locked and your front wheels are moving, so are your back. That is exactly the purpose of a locking diff.

Now becuase we only have a locking center diff, if 3 wheels are on a frictionless surface and say the rear right wheel is not, we're not moving without A-TRAC regardless of center diff locking. The limited-slip diffs are sending all the power to the wheels that can move, so while your front and rear diffs are moving at the same speed no matter what, your rear diff is sending all of its 100% power to the wheel on the frictionless surface because it moves the easiest. A-TRAC sees this, applies the brake to the rear left wheel (the one on the frictionless surface) which creates friction, and allows the right wheel to turn however much the brake is applied to the other wheel. A-TRAC basically evens out the friction as best as possible so the wheel with traction can spin.

If we had all 3 locking diffs there would be no need for A-TRAC, at least for off-roading purposes with all the diffs locked. If any wheel has traction, then you will be able to move because 100% of the power is always going to every one of your wheels. How that power is broken up is all about where the traction is.

 

[Thai]

And I can attest the A-TRAC works well. I got crossed up on a rough switch back on Engineer above 550 where my front left and right rear were off the ground. It paused for a split second while we teetered and it grabbed fairly seamlessly and it walked right up. The Jeeps behind me wanted to know if I had a locker.

Yup, that's the beauty of ATRAC. It works really well for such a "simple" design.

 

[dcampen]

Thai is right on the money. Essentially locking our center diff is more of a 100/100 split than a 50/50 split. So, dcampen, while you are correct, 100% of the power DOES go to the front wheels if they are on a frictionless surface, 100% of the power still goes to the real wheels also.

You can't have more than 100% power. In the example I have given where the center diff is locked and the front wheels are on a frictionless surface _no_ power will go to the front wheels and all of the power (100%) will go to the rear wheels. A locked differential means that the 2 output shafts of the differential will always turn at the same speed. If you have the case of 3 locked differentials than all 4 wheels will be turning at the same speed but the engine power and the work done by each wheel could be distributed in any ratio that sums to 100%

With an unlocked, open differential the constant is that the torque is always the same (50/50 split) on the 2 output shafts of the differential. If one output shaft begins slipping (loses torque) then the torque on the other output shaft will also decrease.

With an unlocked Torsen (or other type of limited slip differential) the ratio of the torque on the 2 output shafts is not a constant but can vary over a range of values dependent on the design of the LSD. If one output shaft begins slipping (loses torque) then because of the design of the Torsen the other output shaft will not necessarily lose torque.

Just remember - if your center diff is locked and your front wheels are moving, so are your back.

Just because your front wheels are moving doesn't mean that any power is going to them. In the case with 3 locked differentials and the front wheels on a frictionless surface while the front wheels will be turning at the same speed as the rear wheels no power is going to the front wheels and no work is being done by them; all of the engine power is going to the rear wheels and all of the work is being done by the rear wheels.

 

[dcampen]

However, anything short of complete frictionless surface, Torsen is good. Thus, in off-roading over severe terrain, it is advisable to lock the center diff to prevent this from happening (however rare that may be). Of course, locking this will also shut off VSC. Remember, ATRAC is STILL active on 4wd models, no matter what you do!

Back to the topic of VSC (and Torsen/ATRAC). I have been locking the Torsen as soon as I leave the pavement which has the effect of also disabling VSC. A recent incident has left me wondering if I should not lock the Torsen (because this disables VSC) untill I get into severe terain.

In the recent incident it was my second day traveling out to a location. The first section of the road was a thin layer of sand and gravel over hardpacked dirt with washboards. Since I was familiar with the road from the previous day I was traveling along at about 50 mph (traveling at a significantly higher speed than the average on a road with washboarding helps avoid the worst effects of the washboard) when another truck suddenly appeared over the crest of a hill and traveling towards me. Because of the sudden appearance of the other vehicle I hit the brakes rather hard and the rear end of the truck slid to the right and directing the truck towards the left. I turned the steering wheel to the right to avoid leaving the road, over compensated and was now looking at leaving the road on the right. After a couple of more corrections I got the truck back under control but for a moment I thought I might be ending up off the side of the road. I wonder, if VSC had been enabled if it would have been of any help in controlling the truck.

 

[Thai]

dcampen, glad that you are still here to tell the story. The answer to your question is: yes and no.

VSC shuts off when you apply the brakes. Please see this old thread for more info:

http://www.toyota-4runner.org/showthread.php?s=&threadid=162

So, in your situation, VSC may not help at all........unless.....

VSC is on. VSC is designed to brake for you to regain control of your vehicle. So, if you are quick and experienced with VSC, then you actually want to keep your foot on the GAS pedal and steer (opposite to using ABS where you brake and steer). VSC will then correct the situation for you (hopefully). Remember, VSC will not alter physics...it will not make a miracle, but it may help you in most situation.

So, in your situation, i would keep VSC on. When you get to the slow and muddy stuff, then lock your center diff.

Remember, it is ALWAYS advisable to keep VSC on when you travel at high speed. I only lock the center diff (VSC OFF) over rough terrain where i won't be going any faster than 10-15 mph. I love VSC for everything else.

 

[Vortec4800]

You can't have more than 100% power. In the example I have given where the center diff is locked and the front wheels are on a frictionless surface _no_ power will go to the front wheels and all of the power (100%) will go to the rear wheels. A locked differential means that the 2 output shafts of the differential will always turn at the same speed. If you have the case of 3 locked differentials than all 4 wheels will be turning at the same speed but the engine power and the work done by each wheel could be distributed in any ratio that sums to 100%

With an unlocked, open differential the constant is that the torque is always the same (50/50 split) on the 2 output shafts of the differential. If one output shaft begins slipping (loses torque) then the torque on the other output shaft will also decrease.

With an unlocked Torsen (or other type of limited slip differential) the ratio of the torque on the 2 output shafts is not a constant but can vary over a range of values dependent on the design of the LSD. If one output shaft begins slipping (loses torque) then because of the design of the Torsen the other output shaft will not necessarily lose torque.


Just because your front wheels are moving doesn't mean that any power is going to them. In the case with 3 locked differentials and the front wheels on a frictionless surface while the front wheels will be turning at the same speed as the rear wheels no power is going to the front wheels and no work is being done by them; all of the engine power is going to the rear wheels and all of the work is being done by the rear wheels.

Each wheel is still getting 100% power, it just can't use more than 100% of it. So while none of the power going to a wheel is being used, that allows the other wheels to 'absorb' the unused power. This is why I use the 100/100 analogy. Each wheel is getting 100% power, but the work being done is what is spliting up the torque. Under normal circumstances, if all wheels are locked then every wheel is getting 100% of the power, but only doing 25% of the work. If each wheel only uses 25% of the power it is given, then the leftover power goes to each other wheel equaling up to the 100%. So back to the frictionless surface on 3 wheels, every wheel is getting 100% power still - but because none of the other 3 wheels are doing work the only wheel with traction uses the 'leftover' 100%. In this case the power transfer is done by physics instead of by a mechanical differential. So the locking differential is a 100/100 power distrubution, 50/50 being used. Just because power is going to a wheel, does not mean the wheel is able to use it (ie less/no traction means less/no power put down).

 

[dancojgl]

Each wheel is getting 100% power, but the work being done is what is spliting up the torque. Under normal circumstances, if all wheels are locked then every wheel is getting 100% of the power, but only doing 25% of the work.

Um, no...

Power is the time rate of doing work.

If a wheel is doing 25% of the work, all of the time, it's getting 25% of the power.

All four wheels can't get 100% of the power, or else you're engine is delivering 400% power.

And don't forget that engine, transmission, and drivetrain internal resistance and friction prevent you from getting 100% of the power to the ground in the first place, no matter how wheels are divying it up...

—Dan

 

[Thai]

This is from G500 manual (i borrowed from MB):

"When the center differential is locked, half of the engine's power is automatically distributed to the front wheels and half to the rear wheels. When the rear differential is locked, power going to the rear wheels is equally distributed, so that both rear wheels turn at the same speed and torque. When the front differential is locked, all four wheels now turn with equal power and torque."

I think that this is a very good explanation...and easy to understand.

 

[Vortec4800]

Um, no...

Power is the time rate of doing work.

If a wheel is doing 25% of the work, all of the time, it's getting 25% of the power.

All four wheels can't get 100% of the power, or else you're engine is delivering 400% power.

And don't forget that engine, transmission, and drivetrain internal resistance and friction prevent you from getting 100% of the power to the ground in the first place, no matter how wheels are divying it up...

—Dan

I know that's not the correct usage of the word power, but its the only word I could think of to describe how its working. Maybe I should change it to read that each wheel is receiving 100% of the torque available from the transmission, not power. The wheel is then taking that torque and using it to do work, and the traction the wheel has is what says how much work that particular wheel is able to do with the torque given to it. Either way each wheel receives the same amount of torque as any other wheel if the differentials are locked.

Does that work better?

 

[epinephrine4R]

2010 4Runner Trail VSC problems

Same here, when turning assertively (not aggressively) on dry pavement, often the truck will automatically selectively activate what it feels is a safer arc. Problem is that it will occassionally pull me into oncoming traffic and of course, it scares me when I am just driving and all of a sudden I lose the ability to control my direction. I spoke extensively with Toyota and the feeling is that it is normal. One tech thought that the larger Trail tires might be at fault. I also think that Toyota purposefully activated the VSC early to mitigate lawsuits if the vehicle under/oversteers particularly after Lexus had an "issue". Besides just deactivation it (remember that the computer remembers that you did this in case there is an accident later) I found that giving a small amount of gas in the corner reduces the activation limit. So, is this a problem just to mine or Trail editions or 2010 4runners?

 

[[email protected]]

traction control

I have 2WD and when I try to get a running start down and then up my driveway in the snow, as soon as the rear wheels begin to slip the traction control takes over and slows the engine and thus the truck. I can only get half way up as all momentum is lost. Would love to shut this feature off. Have also had it slip a little pulling out at red lights when wet and it does the same thing-slows the engine down. Not a good thing when you are trying to move into traffic. Is there an easy fix? Thanks,
Tom

 

[Fred Ritchie]

My '04 SR5, rear wheel drive shows same issue and it can be very dangerous. If I must pull out into traffic (ie:from driveway or side street requiring 90 degree turn while accelerating) the control kicks in and the truck feels like it is suffering a stall. It takes a few seconds, after straightening out, before I can accelerate. In my semi-rural area there are many such 90 degree entries from side streets and driveways on roads w/45, even 55 mph limits. A few seconds delay can get you t-boned and killed if you are not aware of this hesitation.
If, while stopped, before starting the turn I push Trac switch to off, I can make rapid turn into traffic without hesitation/trac control action, as soon as I let the wheel come back to straight forward, the Trac control light turns off and it re-engages. You must remember to turn light off every time you need to pull into traffic if you want to assure no hesitation when it is most dangerous.
I bought mine used in excellent shape but without manual so I assumed this was not working correctly (if I turn it off, I felt it would stay off until I
re- engaged it). Wrong and potentially deadly if you are unaware of this little foible. I too was sincerely hoping for a way that I might control on or off but I gather this is the way it is supposed to be. Now my greatest worry is when my wife might need to use the truck rather than her car since this important point is not embedded in her mind from regular use.
I really am surprised to learn this is intended design/operation. PLEASE let me know if this is something I am causing or if something needs inspection?

 

[AuSeeker]

My '04 SR5, rear wheel drive shows same issue and it can be very dangerous. If I must pull out into traffic (ie:from driveway or side street requiring 90 degree turn while accelerating) the control kicks in and the truck feels like it is suffering a stall. It takes a few seconds, after straightening out, before I can accelerate. In my semi-rural area there are many such 90 degree entries from side streets and driveways on roads w/45, even 55 mph limits. A few seconds delay can get you t-boned and killed if you are not aware of this hesitation.
If, while stopped, before starting the turn I push Trac switch to off, I can make rapid turn into traffic without hesitation/trac control action, as soon as I let the wheel come back to straight forward, the Trac control light turns off and it re-engages. You must remember to turn light off every time you need to pull into traffic if you want to assure no hesitation when it is most dangerous.
I bought mine used in excellent shape but without manual so I assumed this was not working correctly (if I turn it off, I felt it would stay off until I
re- engaged it). Wrong and potentially deadly if you are unaware of this little foible. I too was sincerely hoping for a way that I might control on or off but I gather this is the way it is supposed to be. Now my greatest worry is when my wife might need to use the truck rather than her car since this important point is not embedded in her mind from regular use.
I really am surprised to learn this is intended design/operation. PLEASE let me know if this is something I am causing or if something needs inspection?

I have the same year model, but it's a Limited V8 2WD, I have never experienced what you are describing, unless my Trac Control is just not working, I'm not sure what the issue is you're having but I would say it's not normal and you should have it checked out by a qualified mechanic that's familiar with 4th Gens T4Rs.