I was doing some on-site training recently, and one of the armoured vehicles we were using had an intermittent issue with its ABS (Anti-lock Braking System). Sometimes the light was on; most times it went off and stayed off.
This led to a great session on emergency braking and identifying which technique was necessary depending on the status of the light — and understanding that if the incorrect technique was used for that status, it increased the difficulty of responding accurately and safely to the emergency.
Technique-wise it’s very straightforward. Getting target pressure correct as soon as possible is important under any braking condition; to activate the ABS, enough pressure has to be applied to lock up. Speed sensors identify the lock-up and kick in the system to help prevent lock-up again through a modulator (boxy thing under the bonnet with lots of pipes connected to it).
Maintaining pressure to keep the system active is important. Too much pressure, and you can blow the master cylinder (it starts leaking into the servo). Not enough, and the ABS deactivates, increasing braking distance. Let the modulator do the modulation. Avoid pump or lift-off.
Follow the SSSs:
- Squeeze quickly and firmly to identify activation.
- Stay with the pressure to keep active.
- Stop/Steer as necessary.
As technology improves, so has the evolution of ABS. Multi-terrain systems have evolved to allow the ABS to function differently on lower-traction surfaces. This works well as long as the correct surface has been selected with the MTS selector.
So. What to do if that little orange light is on?
Obviously, this is indicating an issue. With all orange lights, we do have the ability to keep on driving — as long as we are aware of the implications. With ABS, it’s indicating that the system is inoperative, and the box with all the pipes is not going to do the modulation.
The driver now becomes the modulator. Being able to correctly identify the correct target pressure and maintain that pressure without using 100% traction (lock-up) is important.
Threshold Braking is the art (yes, it’s an art form) of being able to understand and respond to vehicle language to maintain a pressure just before the lock-up point. This may need very small changes (think coin thickness) in brake pressure as the vehicle slows down. Modulation. That word again. Avoid lift-off and pumping.