Unlocking ABS

A Bendix wintertime test demonstrates how ESP can maintain control even on slick surfaces.

Maintaining antilock technology properly can help reduce accidents and improve a fleet’s inspection record, both of which will help with insurance rates – along with reducing downtime. Further enhancing equipment by retrofitting stability control carries the process further.

ABS is designed to be self-diagnosing, which has been a boon when it comes to inspection and troubleshooting – 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 impractical, a lit-up ABS malfunction indicator 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-diagnostic 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 mechanism 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 magnesium 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 factory 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 preventing 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 aftermarket, Melletat says.

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Fred Andersky, Bendix’s director of marketing for controls, says technicians 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 havoc with the supply side of the air brake system by washing the lube out of the ABS valves.

Duane Stocksdale, Haldex’s product manager of braking controls, recommends making sure the ABS ECU is connected properly and securely to the trailer wiring harness through the industry-standard 5-pin connector. Also, make sure 7-way connectors are maintained adequately to eliminate corrosion at the connector terminals to ensure proper power flow from the tractor, Stocksdale says. “Ensure that wheel speed sensors are installed properly and functioning on installation, replacement, or upon wheel- end maintenance according to ABS service manuals,” he says.

Stocksdale also recommends use of full-length sensors, rather than short sensors plus extensions, to minimize the number of electrical connections; as well as use of dielectric grease on all electrical, sensor and extension connections.

Scoring fleets
How are fleets doing with ABS maintenance? According to Melletat, research has shown that most fleets can address problems on the tractor side – but on the trailer side, some have difficulty. Warning lights on trailers can be caused by a faulty actuator, a sensor out of adjustment, or an open circuit, he says; fortunately, many such problems cause reduced function rather than disabling the entire system.

Andersky believes most fleets can manage most maintenance challenges, and insists that Bendix is doing all it can to help that happen. A technician can go to www.bendix.com and download ACom software to help with troubleshooting, or request a CD for installation on his computer, he says.

All three manufacturers offer retrofittable ABS for older trailers that are without it. Melletat and Stocksdale say their respective MeritorWABCO and Haldex systems can cost as little as $500. Also, reduced tire flat spotting is an immediate benefit that helps pay for the cost of the system even before it has a chance to improve the fleet’s accident record. ABS also serves as a building block that allows easier installation of stability control.

Since ABS has been required on new trailers since 1998, the population of trailers that do not have ABS is in rapid decline, Stocksdale says. “The fleet should certainly look at the projected lifecycle in determining if such an investment is a sound business decision,” he says.

Stability control
The big news in ABS-related technology today is roll stability control. It’s inexpensive for what it does because it uses the ABS actuators and simply adds a processor and various sensors, combined with refined software, to help prevent rollovers. Melletat says MeritorWABCO’s system combines 4-sensor, 4-modulator ABS with an Electronic Control Unit; a lateral accelerometer; a steer axle sensor that measures steering wheel position; and yaw sensors to tell the ECM how far the tractor and trailer actually are leaning.

“Stability technology builds on ABS,” says Rick Conklin, Bendix’s product manager for ESP and stability control. “It adds sensors to figure out what the driver wants and then uses the ABS system to mitigate the situation when stability is threatened.” Conklin says ABS comes in two types – roll stability (“RSP/RSC”), which reacts mainly to lateral acceleration; and full stability (“ESP/ESC”), which helps prevent a loss of control, especially on slick surfaces.

Haldex’s system uses 4-sensor, 2-modulator ABS plus a pneumatic input from the air suspension so the ECM can calculate trailer load changes, and an integral lateral accelerometer so the ECM can recognize changes in the lateral forces on the vehicle. High-end trailer stability systems actually incorporate adaptive learning into the ECM, Stocksdale says.

Melletat says such systems are most useful on shorter wheelbase tractors such as those with set-back axles, and are even more useful on 4×2 single-axle city tractors. Certain other applications, such a fuel hauling, may see extra benefits, he says.

Stocksdale says the Haldex high-end trailer system sends out brake test pulses to determine when the rollover threshold is being compromised. It applies the trailer brakes on the side opposite the liftoff to slow and stabilize the combination, while also illuminating the brake lights to warn following traffic that the vehicle is slowing.