4WD and ABS

I read this on a website (http://4x4abc.com). Does this apply to the Xterra? On slick paved roads, should I put it in 2WD or 4WD? If this is true, it seems that I should stay in 2WD when I am worried about stopping, and put it in 4WD when I am worried about starting to move forward.

"ABS does not work with part time 4WD systems.

"ABS would work as long as the vehicle stays in 2WD mode. In 2WD all 4 wheels are able to rotate at different speeds (made possible by the differentials) and more importantly in 2WD both axles are allowed to turn at different speeds because the drive shafts feeding power to the axles are not connected.

"As soon as you would shift into 4WD the two drive shafts become connected inside the transfer case and both axles would be forced to turn at the same speed. More importantly, when braking both axles will be slowed down at the same rate (any brake proportioning will be out of force) and the ABS system would get confused. After all the ABS's job is to detect variation in wheel speeds and act accordingly. ABS would not function properly on part time 4WD systems."

The ABS on the Xterra works in 2WD and 4WD.

It does not work below ~6mph though, unless the system engaged above that speed.

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Regards,
Ian

Once again, Ian is right. I "tested" my anti-lock a whole load of times during the last snow storm and it kicked in while in 4x4. In the process scaring the hell out of me...

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Does this not pertain to the "g-sensor" feature in the X's ABS system? I thought this was supposed to correct some of the confusion problem ABS has with 4WD on slick surfaces, like going downhill on gravel. I don't fully understand the mechanism but I thought this was supposed to solve the sort of problem mentioned in this post.

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Not really. The sensor helps the system determine how much braking is still being effected with some tires locked and take advantage of it. In a non-ABS vehicle, you'll typically get better stopping on loose or granular surfaces when the tires are locked because the material can pile in front of the tire and form a dam of sorts. This is true in gravel, snow, sand, and dirt.
The sensor will determine at the moment of lockup if the brakes are still doing a decent job and will modulate less frequently to let small dams build up and lend their assistance.

Brent

Thank you, Brent. I have never had an adequate explanation of what that feature actually accomplished.

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One thing to also remember, if you have a limited slip differential, then if one wheel does lock up, then the limited slip would allow the others to still rotate. I have yet to see a 4wd vehicle that has problems with ABS in 4wd mode.

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