ABS, Dirt Roads, and 4 Runners

[jmans]

I am the proud new owner of a 2004 Toyota 4Runner SR5 with 4WD and a V6. As you know the combination of ABS and dirt roads can be dangerous. In addition to this, it is also a proven fact that ABS system will typically not function properly with 4 Wheel Drive and a locked differential (this may not be the case for a center locked differential). I would like to ask the following questions about my vehicle based on these two facts:

1) When is ABS NOT Active? That is to say, is ABS turned off when the 4Runner is in 4WD LOW and the center differential is locked? Or 4WD High with the center differential locked?

2) When VSC is turned off is ABS also turned off?

3) If ABS is not turned off, how do I stop in a reasonable amount of distance on Dirt and Sand (other then crawling along at an unreasonably slow speed, which does not always guarantee safety)?

4) If ABS is turned off, will the car automatically still pump the breaks?

5) Does break assist (activated by quickly pressing down on the break pedal) still use ABS?

I ask these questions to better understand how to safely operate my vehicle under different road surfaces and conditions.

[Darren]

I'm not sure how many 4th Gen owners are here, so in the meantime, I'll take a stab at some of these.

it is also a proven fact that ABS system will typically not function properly with 4 Wheel Drive and a locked differential
I guess I haven't heard about this. What do you mean exactly? Regardless, the (rear) locked differential wouldn't apply to you, as you eluded to.

ABS is never deactivated, only it's sensitivity is greatly reduced when in low range. I'm not sure about high range. Why don't you try it out before you go speeding on your way and answer all questions exactly to your liking in the meantime? Don't take that the wrong way.

3) Don't go at an unsafe speed to begin with (see above)

5) I'm guessing you mean brake assist. Though, I haven't read about that for quite sometime, I would have to believe it would.

For the highest concentration of 4th Gen owners on a message board, go here.

[jmans]

Originally posted by Darren
I'm not sure how many 4th Gen owners are here, so in the meantime, I'll take a stab at some of these.

it is also a proven fact that ABS system will typically not function properly with 4 Wheel Drive and a locked differential
I guess I haven't heard about this. What do you mean exactly? Regardless, the (rear) locked differential wouldn't apply to you, as you eluded to.

ABS is never deactivated, only it's sensitivity is greatly reduced when in low range. I'm not sure about high range. Why don't you try it out before you go speeding on your way and answer all questions exactly to your liking in the meantime? Don't take that the wrong way.

3) Don't go at an unsafe speed to begin with (see above)

5) I'm guessing you mean brake assist. Though, I haven't read about that for quite sometime, I would have to believe it would.

For the highest concentration of 4th Gen owners on a message board, go here.

LOL

I assure you Darren I am not going to go anywhere at an unsafe speed. I am trying to find out what a safe speed is based on the answers to this questions and hoping that does not mean 2-3 MPH.

As for ABS and a locking Diff, I read this a number of times. Since ABS is trying to sense wheel slippage and spin, it supposedly gets confused by locked diffs (which force all wheels to spin at the same rate and slip unless steering absolutely strait). But I am not sure about locked center diffs.

Thank You I will check with this section of the board.

[Darren]

Originally posted by jmans
Since ABS is trying to sense wheel slippage and spin, it supposedly gets confused by locked diffs (which force all wheels to spin at the same rate and slip unless steering absolutely strait). But I am not sure about locked center diffs.

Oh, okay. This scenario you are describing is when power is being applied, rather than attempting to brake. This would be the TRAC system working by utilizing ABS whereby it attempts to brake a slipping wheel and provide power to those with traction. This is also in context in an off-road environment as opposed to a dirt road or what not. With a rear locker (or front for that matter) scenario you describe, there is no wheel slippage, thus this system has no reason to engage. By locking the center diff, there will be less slippage as well, and your traction system won't be working all the time since you have now gone from AWD to conventional 4WD. Lockers (not the center one) take this to a whole new level.

Again, the above is in reference to off-road situations and has nothing to do with your original question. I essentially have the same system as you and I do know that I can skid quite a bit in 4 low and have, in fact, never had the ABS engage during steep and rocky descents. However, I don't recall if the sensitivity is reduced in 4 high like I mentioned previously. I do know that if your center diff is unlocked (AWD), ABS is still very much active. So yes, all this and the original question remains unanswered!