What's normal behavior for ABS?

I have a 2004 Chevy Colorado 4 X 4 with ABS. Whenever I apply the breaks
on snow/ice/water where the truck even begins to slide at all, the
brake pedal pulses violently and there's a terrible metal-on-metal
grinding sound from underneath the truck.

I understand why the pedal is pulsing, but is it normal for there to be
the grinding noise? I've had other vehicles with ABS and I've never
heard anything like it.

The truck also has a rear locking diff, in case that's useful
information.

Any input appreciated.

Sean

Sean Elkins > writes in article > dated Sun, 05 Feb 2006 20:34:57 -0500:
>I have a 2004 Chevy Colorado 4 X 4 with ABS. Whenever I apply the breaks
>on snow/ice/water where the truck even begins to slide at all, the
>brake pedal pulses violently and there's a terrible metal-on-metal
>grinding sound from underneath the truck.
>
>I understand why the pedal is pulsing, but is it normal for there to be
>the grinding noise? I've had other vehicles with ABS and I've never
>heard anything like it.
>
>The truck also has a rear locking diff, in case that's useful
>information.

There's supposed to be modulation between lock-up and not-quite-locked.
This results in "pulsing" but on the ABS systems I've used it's always well
within human hearing range (maybe 100-200 Hz) so it would be better
described as a "hum".

Metal-on-metal grinding is definitely not normal. I don't know what would
cause it except worn-off pads, and they'd also cause grinding when you brake
on dry pavement.

I assume you don't hear the grinding when you do a quick stop on dry
pavement. Try stopping with the emergency brake (but not hard unless you
want to lock up the wheels). If you get a grinding sound then, you need new
rear brake pads.

-- spud_demon -at- thundermaker.net
The above may not (yet) represent the opinions of my employer.

actually in my experiance a slight metalic sound is mostly normal...and
of course pulsing is normal..its the locking/unlocking brake process ...