Air Brakes System with ABS

imported_John Whelan - October 11, 2015
Air brake abs or antilock brake systems are similar to automotive in principle with wheel sensors, tone wheels and a control module. The difference of course is air brakes compared to hydraulic brakes. On our newer school buses there is an off road switch on the dash to engage the ABS and reduce wheel spin. The results using this system during winter conditions are quite amazing.

We had a driver operating on a back road get stuck a couple of times with one of the International conventional buses requiring a tow truck to pull him out of a ditch. After he was told about the ABS off road switch we never heard from him again. In past years there were differential mechanical locking systems that would not allow wheel spin as well but the steering was effected especially when turning or going around corners.

Another great point about ABS air brakes is there are very few problems that arise. There have been a few air leaks and faulty wheel sensors but nothing really serious causing braking issues. Meritor Wabco is the manufacturer of the ABS air brake system on all of our fleet units and luckily we got our hands on their diagnostic software.

It's really quite easy to use and shows you which wheel has a bad sensor after you hook it up to the diagnostic link on the vehicle. That's the nice thing about manufacturers sharing their harness wiring with other manufacturer components in the chassis so there is just one place to hook the 9 pin connector to .... I have to give them a pat on the back for that. Once you hook up the 9 pin connector to the diagnostic link you're able to read codes from the engine, transmission, body and ABS systems.

Once a vehicle goes off warranty it's very helpful to get into the troubleshooting side of things and feel comfortable doing it. The diagnostic software from each manufacturer is the most important tool of all. Without it you're out of luck trying to find a problem on today's buses, trucks and anything else that runs on the highway.

We have 4 laptops in the shop with software from Cummins, Allison, Wabco, Mercedes and Navistar. Diamond Logic Builder is another amazing software from Navistar that has graphics to enable techs to see the circuits and modules turn on and off for testing and troubleshooting purposes.

ABS is here to stay and it's great technology to help vehicles stay on the road in the winter time. I made a point in the video about the air gap between the sensor and the tone wheel. Sometimes the sensor gets pushed away from it's original position while pulling off the wheel hub. It can be moved easily in the bore that it sits in so it's a good idea to make sure it's pushed snug against the tone wheel after the wheel hub has been installed.

Once the brakes are completed the bus will go for a road test to burnish the shoes and see if there are any problems. The ABS brakes have a separate fault code light on the dash that indicates there is an ABS system fault. Then it's time to take action and hook up the laptop with the ABS diagnostic software.