ABS functional during 4wd operation?

Post by **HenryJ** » Mon Nov 10, 2003 10:20 pm

Split this topic to keep it alive, and searchable-HJ

MikeyZR5 wrote:Cool...thanks for the info. Once we get some ICE here, i will snap a few pics for you all to enjoy...

Another thing to keep in mind....When you are in 4wd the abs system is disabled.

I feel that it is safest to run in 2wd on slick conditions, using 4wd to get moving, or if left in drive very cautiously since stopping distances are increased.

NTXCrew · Post by **NTXCrew** » Tue Nov 11, 2003 6:52 pm

HenryJ wrote:Another thing to keep in mind....When you are in 4wd the abs system is disabled.

Hmmm....

jeramey_pa · Post by **jeramey_pa** » Thu Nov 27, 2003 11:48 pm

HenryJ wrote:
MikeyZR5 wrote:Cool...thanks for the info. Once we get some ICE here, i will snap a few pics for you all to enjoy...
Another thing to keep in mind....When you are in 4wd the abs system is disabled.

I feel that it is safest to run in 2wd on slick conditions, using 4wd to get moving, or if left in drive very cautiously since stopping distances are increased.

Are you sure? I'm positive I was in 4HI one time and I turned off onto a driveway that was coated with slimy mud and when I hit the brakes it locked and my ABS kicked in and brought me to a safe stop. I could be wrong but I'm positive it happened last winter.

Rusty · Post by **Rusty** » Fri Nov 28, 2003 4:51 am

jeramey_pa wrote:
HenryJ wrote:
MikeyZR5 wrote:Cool...thanks for the info. Once we get some ICE here, i will snap a few pics for you all to enjoy...
Another thing to keep in mind....When you are in 4wd the abs system is disabled.

I feel that it is safest to run in 2wd on slick conditions, using 4wd to get moving, or if left in drive very cautiously since stopping distances are increased.
Are you sure? I'm positive I was in 4HI one time and I turned off onto a driveway that was coated with slimy mud and when I hit the brakes it locked and my ABS kicked in and brought me to a safe stop. I could be wrong but I'm positive it happened last winter.

I've had the same thing happen. I don't think the ABS turns off in 4wd, or at least it doesn't on mine. It probably should though, at least the way I would reason it out anyway.

quickbiker · Post by **quickbiker** » Fri Nov 28, 2003 7:54 am

Some vehicles it does shut off. The Dakota I had had warnings in the manual about it. But our S-10's do not have any warnings about that as far as I can see.

Post by **HenryJ** » Fri Nov 28, 2003 8:23 am

jeramey_pa wrote: Are you sure? I'm positive I was in 4HI one time and I turned off onto a driveway that was coated with slimy mud and when I hit the brakes it locked and my ABS kicked in and brought me to a safe stop. I could be wrong but I'm positive it happened last winter.

There is no way that it CAN work with 4wd engaged.
Think about how the antilock brakes work. Sensors determine that a wheel or wheels are turning at different rates while braking. They pulse the pressure going to the wheel/wheels that are locking allowing them to roll and maintain friction with the surface.
When 4wd is engaged there is no way for the front and rear to turn at different speeds, so if one wheel locks they all do (three out of four , if the G80 is engaged), effectively disabling the ABS.
Just be careful. Plan on increased stopping distances on slick surfaces when 4wd is engaged.

quickbiker · Post by **quickbiker** » Fri Nov 28, 2003 8:59 am

Yea, I mean a bit of common sense had to be involved. I would think they would work a bit if open front/rear. I know I am kinda screwed with my Detroits, cause it sounds like my ABS doesn't like my Detroits much, but they still seem to work. If there is snow on the ground, gotta drive accordingly. That's why some of this auto stuff is dangerous, some people think it will compensate for driving abilities, it only helps driving abilities.

Dragonmaster · Post by **Dragonmaster** » Fri Nov 28, 2003 9:19 am

HenryJ wrote:
jeramey_pa wrote: Are you sure? I'm positive I was in 4HI one time and I turned off onto a driveway that was coated with slimy mud and when I hit the brakes it locked and my ABS kicked in and brought me to a safe stop. I could be wrong but I'm positive it happened last winter.
There is no way that it CAN work with 4wd engaged.
Think about how the antilock brakes work. Sensors determine that a wheel or wheels are turning at different rates while braking. They pulse the pressure going to the wheel/wheels that are locking allowing them to roll and maintain friction with the surface.
When 4wd is engaged there is no way for the front and rear to turn at different speeds, so if one wheel locks they all do (three out of four , if the G80 is engaged), effectively disabling the ABS.
Just be careful. Plan on increased stopping distances on slick surfaces when 4wd is engaged.

My ABS works just fine in 4hi, but is disabled in 4lo. When the wheel speed sensors detect front wheel lockup in 4hi, it disengages the front diff and engages abs and then it works just like your in 2wd.

quickbiker · Post by **quickbiker** » Fri Nov 28, 2003 9:30 am

Oh, you got the Auto 4x4. The crews don't have that, luckily.

Dragonmaster · Post by **Dragonmaster** » Fri Nov 28, 2003 9:32 am

quickbiker wrote:Oh, you got the Auto 4x4. The crews don't have that, luckily.

No I don't have auto 4x4.

Post by **HenryJ** » Fri Nov 28, 2003 9:39 am

Dragonmaster wrote: My ABS works just fine in 4hi, but is disabled in 4lo. When the wheel speed sensors detect front wheel lockup in 4hi, it disengages the front diff and engages abs and then it works just like your in 2wd.

Hmmm, that is interesting, I've never heard that.

So does the transfercase switch blink when it disengages?
Do you then have to re-engage 4wd to continue it's operation?

I can understand how that would work for the AWD autotrac transfercase, but don't understand how it would work for ours.

You did mean the transfercase not the front axle right? (the front axle will not disengage quickly enough , or at all with a load on it)

If you do mean the front axle disengages, I still don't understand how that works either.

Enlighten me

Rusty · Post by **Rusty** » Fri Nov 28, 2003 10:15 am

quickbiker wrote:Oh, you got the Auto 4x4. The crews don't have that, luckily.

Actually, I wish mine did have it.

Dragonmaster · Post by **Dragonmaster** » Fri Nov 28, 2003 1:42 pm

HenryJ wrote:
Dragonmaster wrote: My ABS works just fine in 4hi, but is disabled in 4lo. When the wheel speed sensors detect front wheel lockup in 4hi, it disengages the front diff and engages abs and then it works just like your in 2wd.
Hmmm, that is interesting, I've never heard that.

So does the transfercase switch blink when it disengages?
Do you then have to re-engage 4wd to continue it's operation?

I can understand how that would work for the AWD autotrac transfercase, but don't understand how it would work for ours.

You did mean the transfercase not the front axle right? (the front axle will not disengage quickly enough , or at all with a load on it)

If you do mean the front axle disengages, I still don't understand how that works either.

Enlighten me

Sorry, yes I did mean the transfer case. The switch just cuts the vacuum to the transfer case actuator, and will re-engage once the abs has finished working. Nothing blinks, and you don't have to re-engage the 4wd when it's done. It sometimes takes a few seconds to re-engage if you accelerate right away, but it comes back on its own.

TruStinger · Post by **TruStinger** » Sat Nov 29, 2003 8:14 pm

i dont know about you but i got a 2001 crew cab automatic and abs works in every setup 2wd, 4 hi and 4 lo. then again its hard to get up to speed in 4 lo to really try it out so i could be wrong

Post by **HenryJ** » Mon Dec 29, 2003 9:14 pm

Ok, this is not scientific, but I had a chance to try out the ABS on a nice snowy parking lot at the Wallowa Lake Marina.

The ABS seems to work the same in 4wd-Hi as in 2wd-Hi.
I can't tell for sure if it is actually as effective at preventing wheel lock, but stopping distances and "feel" were much the same.

While I would still advise caution while braking during 4wd operation, the ABS does appear to still be functional, and does aid in reducing stopping distances.

I would like a more definitive answer to this , but will have to settle on the fact that it works and is not for me to understand all the details at this point.

Mr.ZR5 · Post by **Mr.ZR5** » Tue Dec 30, 2003 1:56 am

I know for sure that it works in 4hi or lo. in my post about almost getting stuck in the cornfieldi could feel my abs kicking in when i was working my way back out. I would prefer it didn't work.

quickbiker · Post by **quickbiker** » Tue Dec 30, 2003 3:54 am

I know ABS doesn't like lockers! The two get the argues at times.

Conman · Post by **Conman** » Tue Dec 30, 2003 7:58 am

Mr.ZR5 wrote:I know for sure that it works in 4hi or lo. in my post about almost getting stuck in the cornfieldi could feel my abs kicking in when i was working my way back out. I would prefer it didn't work.

I thought I posted my results but it must have been in another thread. I tried this a few weeks ago and the abs was "active" during both 4hi and 4lo. Does it mean it will help, that's another question......

Mine is an 02 if we are keeping tabs.

Cheers,
Con

Dragonmaster · Post by **Dragonmaster** » Mon Jan 05, 2004 9:54 am

yep ABS does work in 4hi (not in 4lo on my truck though). I was coming down a very icy hill today and some bozo started coming up. There was only room for one vehicle to fit between the parked cars on either side. The abs kicked in immediately, and kicked the back end sideways just enough to freak me out about hitting the cars that were parked (but I didn't hit them luckily). the front diff or the transfer case didn't disengage (shown by the tech2 monitored by the gm tech that was riding with me to diagnose a transmission slip)

jeremy · Post by **jeremy** » Fri Mar 19, 2004 7:23 pm

i have an 02 cc and i just got back from a road trip in moab utah, and i was going down a sandy hill, and at the bottom around the corner there stood a big fat cow,

, i was going pretty fast and had to stop in a short distance, and i definitely herd and felts my abs engaging, lucky they did or i would have had a cow in my lap

jeremy

marks10cc · Post by **marks10cc** » Sun Mar 21, 2004 8:14 pm

There is a wire that comes from the transfer case control module to the ABS control module. If I had to guess, I'd say the ABS mode while in 4WD is different than 2WD. I know we have 3 channel ABS, the two fronts are independent while the rear is combined. Is it possible that the ABS while in 4WD is one channel? (all four wheels on-off pump synchronized)

Post by **HenryJ** » Fri Nov 05, 2004 3:27 pm

marks10cc wrote:There is a wire that comes from the transfer case control module to the ABS control module. If I had to guess, I'd say the ABS mode while in 4WD is different than 2WD. I know we have 3 channel ABS, the two fronts are independent while the rear is combined. Is it possible that the ABS while in 4WD is one channel? (all four wheels on-off pump synchronized)

Excellent logic!

How did I miss this post for so long

That would be much nicer on the drivetrain if it does indeed pulse all wheels the same while in 4-hi.

I went looking for this topic after reading an article in the current "OFF-Road Adventures" dealing with the ABS woes.

It left me with questions...

What is the threshold speed for our ABS system? What I mean is , below what speed is the ABS system inactive?

We know that the ABS is still active in 4-hi, is it active in 4-lo? or are the speeds usually below the threshold, if it exists?

There are consequences to deactivating the ABS system, but would a switch to deactivate the system be beneficial for offroading? Or would it even be needed?

I know that on loose material skidding the front tires can build a block that slows you faster than the ABS would.
Another ABS concern would be while tricycling. I would not want the ABS thinking that the raised tire was skidding especially on a steep downhill slope. That might make for a faster than planned decent

So just how smart is our ABS system?

kf6kmx · Post by **kf6kmx** » Sat Nov 06, 2004 10:22 am

HenryJ wrote:Ok, this is not scientific, but I had a chance to try out the ABS on a nice snowy parking lot at the Wallowa Lake Marina.

The ABS seems to work the same in 4wd-Hi as in 2wd-Hi.
I can't tell for sure if it is actually as effective at preventing wheel lock, but stopping distances and "feel" were much the same.

While I would still advise caution while braking during 4wd operation, the ABS does appear to still be functional, and does aid in reducing stopping distances.

I would like a more definitive answer to this , but will have to settle on the fact that it works and is not for me to understand all the details at this point.

Since its 4wheel ABS, and completely computerized.. I wonder if its 'guessing' about a lockup in 4wd by the sensors dropping too rapidly and then pules the entire system?? Since in 4wd, theory anyway, if one wheel locks you end up locking them all.. by the same reasoning that it cant sense a single wheel because of them tied together, a single cant slide on its own, so the whole system would go into ABS...
Just a thought...

kf6kmx · Post by **kf6kmx** » Sat Nov 06, 2004 10:32 am

HenryJ wrote:
I went looking for this topic after reading an article in the current "OFF-Road Adventures" dealing with the ABS woes.

It left me with questions...

What is the threshold speed for our ABS system? What I mean is , below what speed is the ABS system inactive?

We know that the ABS is still active in 4-hi, is it active in 4-lo? or are the speeds usually below the threshold, if it exists?

There are consequences to deactivating the ABS system, but would a switch to deactivate the system be beneficial for offroading? Or would it even be needed?

I know that on loose material skidding the front tires can build a block that slows you faster than the ABS would.
Another ABS concern would be while tricycling. I would not want the ABS thinking that the raised tire was skidding especially on a steep downhill slope. That might make for a faster than planned decent

So just how smart is our ABS system?

Well, I dont know a threshold, but I know my '03 goes pretty slow with ABS on.. I had an idiot pull out in front of me when I was making a turn (the typical, your turning right, with signal on and a green light, and they decide to pull out of the parking lot across the street and take that lane instead of you.. after waiting for the huge empty gap in front of you to go by, and no one for a mile behind you

) and ABS definetly came on.. I was doing under 15 at the time..probably around 10.. ABS didnt stay on long, but it definetly kicked on.
The road surface was rough, and pre-shock change, so I think I probably had a rear wheel bouncing up pretty high and loosing traction to the road as I put on the binders..