4X4 and ABS brakes?

ABS and 4X4?
?03 4X4 Z71 first time I have had it off the pavement.
Took a 80+ miles trip on Forest Service roads, tried some small
hills (no lift), and keeping it sane I was by myself.
I hit a washboard on a gravel road with some good holes.
When I hit the brakes it felt like my front end
was coming off and my brake paddle lost some pressure.
I have just over 1k on new rotor's and pads on all 4. After I change my
shorts and few choice words I checked the AVY out.
It all seemed fine, so on I go. Hitting the brakes often, all
normal. Same thing happen next washboard, no problem
on smother gravel but I could make it happen any time
on washboards or hitting holes. This happened in 4Auto
and 2 wheel. I switched bake and forth. So trying to make
this happen to try and feel what was going on, it seem the
brakes were modulating so that is why I'm hopping it is
the ABS.
So being new to ABS on a 4X4 is this the ABS kicking in,
or do I have something else going on?
Checked it out when I got home all normal.
I drove about another 80 miles later in the day on freeway
and in town no problems.
JV

I have had this happen a Few time (One to many times) off Road and also in rain and Snow conditions.
The ABS engaging feels like the Brake peddle under your foot is ratchiting or Farting. Yea I said Fart

The only solution to eliminate this is to pull the ABS fuse then remote the Fuse through a Switch.
When off road turn the ABS off. However this may throw a ABS Code. So have a Code reader to clear after you get back on pavement.


Just My $0.02

There is an issue with the front ABS sensors on some of the early Av models. I think there was even a recall on it. The front wheel speed sensors rust and give screwy readings to the computer, which thinks the wheel is sliding so it modulates the brakes. I had mine start to go out a couple years ago, and the only time I would notice it was when stopping on gravel while making a turn (like I do when pulling into the driveway.) The brakes start modulating, the pedal moves up and down slowly while rapidly buzzing, and you don't stop anywhere near as quickly as you would hope.

I would suggest both of you (and anyone else who has had this happen) to get your front ABS sensors checked out. I ignored it as a fluke occurrence at first, and it only got worse and more frequent over time. This has important safety consequences, get it checked out.

-- SS

ShapeShifter,SRFNSNO ,
Thanks for the reply. I will have all the
sensors checked out and look into the recall.
Is there any feed back on SRFNSNO suggestion on
disarming the ABS when 4wheeling I have a code reader.
Any feed back about 4wheeling and ABS on a proper working
system would be appreciated.
My first experience with ABS was when my wife had a '91 Safari van.
It had a limited-slip rearend loved it in the snow and ice
once I got the hang of the ABS. This my first in an off-road
4X4 outing.
JV

I have had mine checked a few years back when they issued the Recall.
Also when I replaced the Wheel bearings recently.

I have the issue on Muddy Slope Side hills and Snow Coverd hills. when bracking is need to stop.
as long as the AV is sliding the brakes burp at you. and there is also no control of steering.
Best choice has been no brake and motor out of slide.

Hey JV,
  My brakes do the exact same thing on the washboard logging roads under heavy brake/or heavy brake while turning. I don't know about the recall for your year but I can say that what you described sounded like normal ABS Pump/Grind to me. I've had 2 cars and now this Avy with ABS and they all have done it. Haven't tried it in 4x4 or Auto4 yet though.
Brian

TheArsenal33 said:

but I can say that what you described sounded like normal ABS Pump/Grind to me. I've had 2 cars and now this Avy with ABS and they all have done it.

Click to expand...

Yes, it is exactly like the normal ABS action. The difference is the conditions under which it happens. When you are in a slippery conditions and you get on the brakes too hard, you expect it to happen. But you don't expect it when you are lightly braking under marginally slippery conditions. For example, on the gravel I mentioned before, with heavy braking you would expect the ABS to kick in, but not when you are using less than a quarter of the brake pressure that would normally activate them.

The ABS system works as expected, but the failing wheel speed sensor makes the system very "twitchy" and hypersensitive at random times.

-- SS

Ahhh Good Call SS! 
Attention to detail is the key here.

ShapeShifter said:

The ABS system works as expected, but the failing wheel speed sensor makes the system very "twitchy" and hypersensitive at random times.
-- SS

Click to expand...

If that's what your getting JV, then I apologize for calling it normal.
I can see where you go to do a normal stop and the ABS starts "buzzing" would be quite a shock to the driver.
Even when I do some light wheeling and the ABS activates I don't like the sound of it.

TheArsenal33 said:

I can see where you go to do a normal stop and the ABS starts "buzzing" would be quite a shock to the driver.

Click to expand...

Yes! The few times it did it to me was during a gentle stop on gravel, and when the ABS kicked in it acted like it was on glare ice -- pumping like crazy, and hardly slowing down at all. 

The only saving grace was that I was doing less than 10 miles an hour, with plenty of space in front of me, or else the result could've been quite different! 

-- SS

TheArsenal33, ShapeShifter,
I do not now what normal is with ABS and trying to stop on an
uneven surface. So all your input is so important to us all.
It just made me SO    to think I screwed up on putting my brakes on.
ShapeShifter yes I had not put much pressure on the brake paddle
when this happened the first time. That is what   me the most
But felt better when I could make this happen when I wanted it to.
Checked it all out when I got home all is well.
ShapeShifter so I need a shop to check out my sensors, or can I look on here and find a
thread also can I replace them if needed?
There is one thing that you two brought out was the ABS buzzing I do not remember
that happening.
So I'm hopping some harden 4 wheelers would jump in here on their experiences.   
I would like to do some real 4X4ing, Disarm or learn to deal with it.
JV

JVZL1 said:

There is one thing that you two brought out was the ABS buzzing I do not remember that happening.

Click to expand...

I didn't mean buzzing as in a warning signal or beeper. I meant the distinctive chatter/rattling noise associated with the rapid pulsing of the ABS system.

There very well could be a thread on servicing/replacing the sensors. A bit of searching may turn up some good information. (I'm on a slow connection for the next few days, and anything but the most basic browsing is a painful slow experience.)

-- SS

I have experienced the ABS chatter before. Yes it was the
rattling, violent pullsating, and lack off stopping that made me have to change my pants.
Well thanks again and I hope this thread will help others.
Still would hope some of the more experience off-roaders would chime in
on how they handle ABS and off-roading.
I will search and post any links I find on ABS sensors.
JV

:     
Some links I found on site, ABS Wheel speed sensors.

http://www.automotive.com/2003/12/chevrolet/avalanche/recalls/index.html
Look up recalls and research all vehicles.

http://www.chevyavalanchefanclub.com/cafcna/index.php/topic,38086.0.html
ABS 101

Hub Assembly ABS Sensor Investigation
http://www.ebearing.com/news2005/053101.htm
Good read


http://www.mycarstats.com/safetystation.asp
http://www.internetautoguide.com/auto-recalls/09-int/2002/chevrolet/avalanche/index.html
More on recalls on vehicles

This is a soon to do MOD! 
http://www.chevyavalanchefanclub.com/cafcna/index.php/topic,68819.0.html

Just no easy fix. Time to pull out the service manual and see what I can break.
Will post up date.
JV

JVZL1 said:

Some links I found on site the ABS Wheel speed sensors.

Click to expand...

Good research, thanks for posting your results! 

-- SS