Unlocking ABS
110 Commercial Carrier Journal August 2008 A Bendix wintertime test demonstrates how ESP can maintain control even on slick surfaces. M aintaining antilock tech-nology properly can help reduce accidents and improve a fleet's inspection record, both of which will help with insurance rates along with reduc-ing downtime. Further enhancing equipment by retrofitting stability control carries the process further. ABS is designed to be self-diag-nosing, which has been a boon when it comes to inspection and trouble-shooting but it also has opened the door for inspectors when it comes to giving out citations. While active testing of ABS with specialized equipment at roadside is impracti-cal, a lit-up ABS malfunction indica-tor lamp is considered grounds for a citation on any vehicle new enough for ABS to be legally required. Maintaining ABS ABS maintenance is pretty simple because of the system's self-diagnos-tic capability, says Mark Melletat, MeritorWABCO's senior manager of marketing and customer service. There is no preventive maintenance as far as we are concerned except for the wheel speed sensor. The mecha-nism is self-adjusting, he says, and if a technician gently pushes it down until it contacts the wheel, it will adjust itself properly to the proper 0.040-inch gap unless it's frozen in its holding block. Always adjust it this way when servicing the brakes, Melletat says. The holding block is ferrous with a brass fixture inside. A spring clip provides the holding force. However, if a high dose of mag-nesium chloride has corroded the fixture, it may expand and crush the sensor, he says; it no longer will adjust properly on its own, or be possible to adjust it manually. It's thoroughly lubed at the fac-tory and considered to be lubed for life, but tell your technicians to check it, Melletat says. In a few applications, like city transit, it may be advisable to clean it up and relube it periodically. Since ABS valves handle air, clean air will preserve them by prevent-ing corrosion, so servicing the air dryer as required will help reduce failures. Air dryers normally work well and provide reliable service unless the air compressor is worn and passing oil, thus contaminating the desiccant. Check compressor performance with a blot test for the air dryer that's available in the after-market, Melletat says. Fred Andersky, Bendix's director of marketing for controls, says tech-nicians should shut off the vehicle and then turn the ignition back on while listening for the chuff test, which runs the ABS valves through a full operating sequence. There will be an audible change in the sound when there is a problem, Andersky says. If there is a leak, you'll hear air being expelled. Bendix offers a remote diagnostic unit, or RDU, to make it easier for technicians to interpret trouble codes and enable them to do so without using a laptop, Andersky says. Also, air dryer performance depends upon proper spec'ing and brake system maintenance, he says. He also warns against using alcohol, which plays Antilock brakes roll on and offer ways to cut operating costs By John Baxter Unlocking ABS