Part-time 4hi : what's won't work? (ABS, VSC, TRAC)

[Arterisk]

Hi,

After reading many pro's and con of the 4WD part-time of the 5-gen runner, I'm trying to understand what won't work when I'm using the 4hi?

Some sites says's nothing will work, so no ABS, no VSC and no TRAC? Is that true?

So let's say I'm on an iced & snowy road, and that I'm driving at 30-40mph, should I enable 4hi or just stay in 2hi? (I have an SR5)

 

[westwind77]

Hi,

After reading many pro's and con of the 4WD part-time of the 5-gen runner, I'm trying to understand what won't work when I'm using the 4hi?

Some sites says's nothing will work, so no ABS, no VSC and no TRAC? Is that true?

So let's say I'm on an iced & snowy road, and that I'm driving at 30-40mph, should I enable 4hi or just stay in 2hi? (I have an SR5)

In 4HI, ALL systems work (ABS, VSC, TRAC). That being said you can manually disable TRAC or VSC & TRAC if you want to. To my knowledge ABS is never deactivated in any setting, 4LO or 4HI.

Also in 4Low, quoted from the manual:
"When the front-wheel drive control lever is shifted to L4
VSC and TRAC (TRC) are automatically turned off."

 

[Arterisk]

thanks for the answer!

About ABS : I've read that ABS can't work in 4wd part-time since the ABS system rely wheels rotation speed to engage the ABS system. But since all wheels are rotating at the same speed in 4hi part-time, it can't work?

edit : here's the article :
http://www.4x4abc.com/4WD101/ABS_parttime.html

 

[scanny]

So let's say I'm on an iced & snowy road, and that I'm driving at 30-40mph, should I enable 4hi or just stay in 2hi? (I have an SR5)

You should use 4hi, as Westwind said VSC & TRAC work in 4hi. Although it might be a good idea to turn off TRAC when you going through deep show. Oh, and if you turn off TRAC alone in 4hi it will be automatically turned back on when you reach 30 mph.

 

[scanny]

thanks for the answer!

About ABS : I've read that ABS can't work in 4wd part-time since the ABS system rely wheels rotation speed to engage the ABS system. But since all wheels are rotating at the same speed in 4hi part-time, it can't work?

Well, when I tried to stop on fresh snow in winter I learned that ABS kicks in pretty fast in 4HI. At least it stats clicking and break pedal pulsates a little bit.

 

[Ryan_S]

I've read that ABS can't work in 4wd part-time since the ABS system rely wheels rotation speed to engage the ABS system. But since all wheels are rotating at the same speed in 4hi part-time, it can't work?

That sort of makes sense, you may lose some ABS effectiveness.... however part time 4WD without locking differentials (axle differentials, not center differential ) basically makes one front and one rear wheel turn at the same time. wheels on the same axle can still turn at different rates, due to the open axle differential.

You can see this in some of the videos where people have one wheel off teh ground. The wheel in the air will spin freely. At that point, ATRAC will kick in, if turned on, which is basically the ABS stopping that wheel to transfer torque over to the wheel sitting on the ground.

here's a good video demonstration: http://www.youtube.com/watch?v=EMXghBOUMMY&feature=related
the front right wheel is spinning independently of the front left.

the same can happen when braking and trying to stop. ABS can brake the left/right wheels independently.

 

[JB.]

So let's say I'm on an iced & snowy road, and that I'm driving at 30-40mph, should I enable 4hi or just stay in 2hi? (I have an SR5)

I'd suggest 2WD until 4WD becomes necessary. Meaning stuck or threat of being stuck.

3 reasons:
1. The one you mentioned; reduced abs function effectiveness.
2. Reduced turning traction due to slight front wheel skid.
3. It's easy to get going too fast for conditions with 4WD.

 

[scanny]

I'd suggest 2WD until 4WD becomes necessary. Meaning stuck or threat of being stuck.

3 reasons:
1. The one you mentioned; reduced abs function effectiveness.
2. Reduced turning traction due to slight front wheel skid.
3. It's easy to get going too fast for conditions with 4WD.

I disagree. First of all you get way better vehicle stabilty in 4WD on showy roads. Second is that sometimes it's too late to switch to 4x4 when you already stuck and you never know what is ahead on snowy road. About going too fast - it's true, but I've seen 2WD cars in the ditch too : )

And since we are talking about SR5 the 4x4 should be engaged for at least 10 miles every month, so slippery road conditions is a good thing to keep transfer case lubricated.