99' Chevy Silverado ABS malfunction

I own a '99 chevy silverado pick up with a 4.8 liter V8, auto trans, 4X4,
standard cab, shortbox with 80k miles on it.
For about a week now the ABS "goes" when stopping. It only occurs at or just
below 5 mph, never at higher speeds and on dry clean roads (Obviously when
it is NOT needed). It seems to occur even under extremely light pedal
pressure (just enough to say. turn on the brake lights but apply minimal
stopping effort).
The rotors and pads are all new within the last 6 months and are wearing
evenly.
I have checked all the electrical connections from the wheel speed sensors
and all look clean and uncontaminated or corroded.
The ABS malfuntion indicator light is NOT lit.
Does anyone have an idea of what to look at next?


--
--
Alan Gallacher
Born to Tinker!

On Sat, 18 Dec 2004 14:16:48 -0500, "Anumber1"
> wrote:

>I own a '99 chevy silverado pick up with a 4.8 liter V8, auto trans, 4X4,
>standard cab, shortbox with 80k miles on it.
>For about a week now the ABS "goes" when stopping. It only occurs at or just
>below 5 mph, never at higher speeds and on dry clean roads (Obviously when
>it is NOT needed). It seems to occur even under extremely light pedal
>pressure (just enough to say. turn on the brake lights but apply minimal
>stopping effort).
>The rotors and pads are all new within the last 6 months and are wearing
>evenly.
>I have checked all the electrical connections from the wheel speed sensors
>and all look clean and uncontaminated or corroded.
>The ABS malfuntion indicator light is NOT lit.
>Does anyone have an idea of what to look at next?
>
>
>--

"goes" is the best description of the issue you can give us? Is it
physically leaving you and the vehicle behind and heading off in to
bad neighborhoods alone after dark? Sorry but I don't understand what
the fault is here.

Steve B

Have it scanned on an abs capable scanner and look for one of the ft wheel
sensors dropping out before the others at low speeds, this may take a
co -pilot to watch the scanner as the truck is being driven, pay attention
at 6 mph down, If one shows premature drop out of wheel speed readings,
many times cleaning the mounting area of the sensor where it fits to the hub
and putting anti corrosive grease at that area will correct this, if not the
sensor is usually bad
"Anumber1" > wrote in message
...
>I own a '99 chevy silverado pick up with a 4.8 liter V8, auto trans, 4X4,
>standard cab, shortbox with 80k miles on it.
> For about a week now the ABS "goes" when stopping. It only occurs at or
> just below 5 mph, never at higher speeds and on dry clean roads (Obviously
> when it is NOT needed). It seems to occur even under extremely light pedal
> pressure (just enough to say. turn on the brake lights but apply minimal
> stopping effort).
> The rotors and pads are all new within the last 6 months and are wearing
> evenly.
> I have checked all the electrical connections from the wheel speed sensors
> and all look clean and uncontaminated or corroded.
> The ABS malfuntion indicator light is NOT lit.
> Does anyone have an idea of what to look at next?
>
>
> --
> --
> Alan Gallacher
> Born to Tinker!
>
>




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"Steve B." > wrote in message
...
> On Sat, 18 Dec 2004 14:16:48 -0500, "Anumber1"
> > wrote:
>
>>I own a '99 chevy silverado pick up with a 4.8 liter V8, auto trans, 4X4,
>>standard cab, shortbox with 80k miles on it.
>>The rotors and pads are all new within the last 6 months and are wearing
>>evenly.
>>I have checked all the electrical connections from the wheel speed sensors
>>and all look clean and uncontaminated or corroded.
>>The ABS malfuntion indicator light is NOT lit.
>>Does anyone have an idea of what to look at next?
>>
>>
>>--
>
> "goes" is the best description of the issue you can give us? Is it
> physically leaving you and the vehicle behind and heading off in to
> bad neighborhoods alone after dark? Sorry but I don't understand what
> the fault is here.
>
> Steve B

The anti-lock system activates, (the anti-lock pump operates, runs, pulses
the hydraulic pressure etcetera) when I am braking for a stop.
The system "goes off" every stop on clean (not sand, dirt, leaves or gravel
covered), dry pavement. It only activates at or below 5 mph. It has never
falsely activated above 5 mph.
It is not sensitive to pedal pressure or braking effort. I can feel and hear
the anti-lock pump running with minimal pedal pressure (I.E. not enough
pressure to slow the truck but enough to set the anti-lock system "off") as
the vehicle speed drops below 5 mph.
I think the problem has to be related to the wheel speed sensors giving a
false or uneven reading to the ABS computer.
I checked the resistance of all the wiring between the wheel speed sensors
and the ABS control module to rule out broken wires. I visually inspected
every connection to verify good, corrosion free connectors. No corrosion was
found and all of the wiring shows very minimal to no resistance with my
Fluke multi-meter.
I am hoping someone can steer me towards anything I may have missed.
I suspect I will have to take it to a shop with the means to read the wheel
speed data to point me toward the wheel speed sensor that is bad. I really
don't want to replace sensors or the control module randomly.
Thanks for your interest, I hope I have explained the symptoms with enough
detail for someone to understand what is going on.
Thanks

--
--
Alan Gallacher
Born to Tinker!

In article >,
"Anumber1" > wrote:

> "Steve B." > wrote in message
> ...
> > On Sat, 18 Dec 2004 14:16:48 -0500, "Anumber1"
> > > wrote:
> >
> >>I own a '99 chevy silverado pick up with a 4.8 liter V8, auto trans, 4X4,
> >>standard cab, shortbox with 80k miles on it.
> >>The rotors and pads are all new within the last 6 months and are wearing
> >>evenly.
> >>I have checked all the electrical connections from the wheel speed sensors
> >>and all look clean and uncontaminated or corroded.
> >>The ABS malfuntion indicator light is NOT lit.
> >>Does anyone have an idea of what to look at next?
> >>
> >>
> >>--
> >
> > "goes" is the best description of the issue you can give us? Is it
> > physically leaving you and the vehicle behind and heading off in to
> > bad neighborhoods alone after dark? Sorry but I don't understand what
> > the fault is here.
> >
> > Steve B
>
> The anti-lock system activates, (the anti-lock pump operates, runs, pulses
> the hydraulic pressure etcetera) when I am braking for a stop.
> The system "goes off" every stop on clean (not sand, dirt, leaves or gravel
> covered), dry pavement. It only activates at or below 5 mph. It has never
> falsely activated above 5 mph.
> It is not sensitive to pedal pressure or braking effort. I can feel and hear
> the anti-lock pump running with minimal pedal pressure (I.E. not enough
> pressure to slow the truck but enough to set the anti-lock system "off") as
> the vehicle speed drops below 5 mph.
> I think the problem has to be related to the wheel speed sensors giving a
> false or uneven reading to the ABS computer.
> I checked the resistance of all the wiring between the wheel speed sensors
> and the ABS control module to rule out broken wires. I visually inspected
> every connection to verify good, corrosion free connectors. No corrosion was
> found and all of the wiring shows very minimal to no resistance with my
> Fluke multi-meter.
> I am hoping someone can steer me towards anything I may have missed.
> I suspect I will have to take it to a shop with the means to read the wheel
> speed data to point me toward the wheel speed sensor that is bad. I really
> don't want to replace sensors or the control module randomly.
> Thanks for your interest, I hope I have explained the symptoms with enough
> detail for someone to understand what is going on.
> Thanks

Jack up each front wheel and check the wheel bearings for any
play, replace any that are loose. If the wheel bearings are still
serviceable you need to remove the wheel speed sensors and clean
the area where they mount down to bare metal. Once clean, apply a
coating of waterproof grease to the mounting area and re-install
the wheel speed sensor.

Common problem. Rust causes the wheel speed sensor to heave away
from the mount, the sensor will still register the correct
frequency, but the amplitude of the signal will be weaker, the
ABS computer reads both frequency and amplitude of the signal at
speeds below 7 MPH for increased accuracy.

"aarcuda69062" > wrote in message news:nonelson->
Common problem. Rust causes the wheel speed sensor to heave away
> from the mount, the sensor will still register the correct
> frequency, but the amplitude of the signal will be weaker, the
> ABS computer reads both frequency and amplitude of the signal at
> speeds below 7 MPH for increased accuracy.

Thanks!
That was it.
I removed the front wheelspeed sensors, cleaned 'em, hit the mounting
surfaces with some emery cloth, applied a bit of sil-glide, reassembled
and... TA-DA!
No more unwanted ABS applications.


--
--
Alan Gallacher
Born to Tinker!