[AL]

I have never heard my ABS, but I do know instead of a grumbling noise you are more likely to hear air pulsing.

The way the ABS works on our coaches is the module that is between the relay valve and the brake chamber gets a signal from the ABS control module that one of the wheels is beginning to turn slower than the others. That is a sign to the control module the wheel is about to lock up and skid.

The control module then causes the air from the relay valve to the braking module to be shut off, and the air pressure between the braking module to the brake chamber to be released to atmosphere, in which case the wheel is now rolling free so the braking module goes back to allowing air to the brake chamber. If the imending lockup is sensed again this venting of brake chamber pressure to atmosphere occurs again until all wheels are slowing at the same rate.

I suspect you will hear air escaping as a result but not a grumbling noise. I have no idea what that noise could be.

[Tom]

I REPLACED FRONT WHEEL SEAL I MUST HAVE MOVED SENCER PART OF TIME WHEN I USE BRAKES STARTING OFF I GET THE NOISE YOU ARE HEARING THE ABS LIGHT COMES ON TO CHECK BRAKES I PUMCH BUTTON ON CONTROL PANEL ON LEFT OF DASH LIGHT STAYS ON NOISE STOPS

[Archived]

I was braking hard on a secondary road when I heard the sound. There may have been some gravel on the road. It sounded just like the ABS on car but at a lower frequency (5 Hz or so).

Prevost checked the front disc brakes and suspension and replaced the brake pads and the upper A arms which showed some bushing wear. The bus tracks better with the A arms replaced and I have not heard the “noise” since. Maybe what I heard was he worn A arm bushings as the ABS engaged and released.

Gerald