If a brake problem is tripping the malfunction indicator lamp (MIL), the first impulse usually is to focus on a vehicle’s active braking systems. However, the source of the problem may well be the pads, rotors, drums and shoes of the vehicle’s mechanical braking system.
“On today’s vehicles, active braking systems are becoming more complicated and rely even more heavily on properly functioning mechanical brake systems,” says Greg Neuenfeldt. He is a trainer for Tenneco Inc., supplier of Monroe Brakes friction products.
Neuenfeldt places active braking systems into two “buckets.” One holds the systems that activate when the brake pedal is depressed. Among the most familiar of these are antilock braking systems (ABS). “We’re using wheel speed sensors to try to keep those tires from locking up by grabbing hold of the brake for that wheel. If that wheel starts to lock up, it will release a bit of pressure and let that wheel get rolling again.”
Emergency brake assist is an example of a newer active system. “This allows the driver to not worry about over applying the brake. The computer will take over and modulate the amount of brake pressure to stop the vehicle safely,” says Neuenfeldt.
Even newer is brake force distribution, which enables the braking system to adapt to the load in the vehicle. For example, if there are passengers in the back seat, the system applies more braking pressure to the rear. “It’s a very smart system where it’s detecting weights in the vehicle in conjunction with ABS to try to make those stopping distances as short as possible.”
Proactive brake systems
Neuenfeldt places systems that are active when the driver is pushing the accelerator into the “proactive” bucket. Traction control is one example. “If the driver is accelerating and the tire is slipping, the computer system cuts back on the throttle a bit, which often helps the tire regain traction with the road.” If reducing engine power doesn’t work, the system will take other steps to help the tire grip the road, up to engaging the brake of the wheel that’s spinning.
Automatic emergency braking is another system that activates when the driver is pressing the accelerator pedal. “The vehicle will apply the brakes on its own, without the driver touching the brake at all,” says Neuenfeldt. “That system is using the brake system on the vehicle without the driver depressing the brake pedal.”
Many new luxury vehicles have sensors in the windshield to detect rain. Along with turning on the wipers, the system keeps the car’s brakes dry. “It will put the pads up close to the rotors, not enough to cause the vehicle to slow down, but just enough to wipe those rotors off and keep them dry,” says Neuenfeldt.
Lane-keep assist, also called lane departure, applies the brakes on the side of the vehicle opposite where a driver is drifting. “If you’re starting to drift off the road towards the shoulder, for instance, usually it will give an alarm or vibrate the steering wheel. In a worst-case scenario it will start to apply the left side brakes on both the driver-side wheels to pull the vehicle back into the lane,” says Neuenfeldt.
Prevent the corrosion
When the MIL illuminates, consumers, technicians and service advisors often assume the fix will involve significant sensor- or computer-related expense. But the source of the problems, says Neuenfeldt, is often corrosion in the mechanical braking components.
“In every state in the country, we get corrosion. A corroded wire or a brake component that is rusted and not operating properly will affect active braking systems as well as stopping distances.”
Neuenfeldt says lubricating the moving components of the mechanical portion of the brake system serves two purposes.
“Lubrication enables the components to slide and move so that when the active braking system makes adjustments, things are moving like they’re supposed to. When you’re doing a brake service such as replacing pads or shoes, all these moving components need to be cleaned properly and lubricated properly. The other point is lubrication prevents corrosion. One of the worst things for brakes is corrosion. And it’s fine if brake components look rusty as long as they have good lubrication at the friction points.” ■