Low-tech precautions keep brakes performing in high-tech systems
Overland Park, Kan.—The industry has come a long way from four-drum, single-reservoir master cylinder braking systems. Today’s braking systems are an integral part of newer technology such as electronic stability control and advanced driver assistance systems (ADAS), correcting for conditions such as oversteer by applying a brake to one wheel or using automatic emergency braking to stop before the driver even realizes traffic is at a standstill.
But the task of keeping the braking system performing its part in sophisticated systems remains simple: keep the brake fluid fresh and pay attention to all components in the braking system when performing a brake job, said Karl Schneider, senior training instructor for Robert Bosch LLC’s automotive aftermarket in North America. Schneider spoke on the evolution of braking technology, antilock brake systems (ABS), traction control, and stability control (such as Bosch’s Electronic Stability Program, or ESP) in his recent “Brake Technology Update” class at the Vision Hi-Tech Training event.
“When they said, ‘Flush your brake fluid’ 15 years ago, the common response was, ‘What are they talking about?’ Manufacturers finally started to catch on — with the advent of ABS systems, traction control systems, and now ESP systems — that now we need really good, clean brake fluid in the systems. If brake fluid has a lower boiling point, or the quality is not up to OEM standards, it can affect the way that ABS unit or that ESP unit works,” Schneider said.
Brake fluid is hygroscopic, which means it absorbs moisture over time that lowers the boiling point, he pointed out. There are several testing methods to test brake fluid for high moisture content, including a brake fluid electrical continuity tester or test strips, while brake flush machines can automate the fluid exchange process.
“At the onset of ABS, it wasn’t designed to get you to stop in a shorter distance; it was designed so you would be able to steer in the direction you wanted to go and hopefully avoid the situation you’re in. Any driver, even a new one, will steer away from danger; it’s just natural for us. But today’s ABS with ESP will stop that vehicle in a very short distance.”
Today’s different braking feel can cause customer concerns
Today’s master cylinders can be more complex, including Bosch’s integrated power brake, which combines brake force boosting and ESP (electronic stability program/ABS/traction control) functions in a single unit, but their design also results in less wear.
“The old master cylinders went bad all the time,” he said, because of a design that included the piston’s rubber seal moving past the reservoir’s passage in the bore, causing seal wear. Today’s units are a central valve design, which means no rubber seal has to slide past a passage. But newer designs have a spongier feel.
“This has raised a problem with some of the customers I’ve had in the past, thinking there was a problem with their brakes. In the past, you would hit the brake pedal, and it would be a solid, hard pedal; it wouldn’t move in older systems. I have one guy who still comes by, and he swears something’s wrong with his brakes, because the pedal drops. I tell him it’s working as designed.”
‘Complete brake job’ is important
The related systems rely on the as-designed performance, so skimping on the quality of brake pads or not installing new hardware can mean the brake system will not perform well now or down the road, Schneider said.
Brake hardware in excellent condition is important to allow calipers and pads to move freely. Rubber seals can start to crack as they age, allowing contaminants into the slides. The bracket, slides, and anti-rattle clips should be checked for wear and replaced as needed.
“For brake pads, you can look for telltale signs of something going wrong: wear at an angle, or grooves in the surface; or pad separation, where the lining separates from the steel backing, usually on low-mileage vehicles that sit a lot.”
Vehicles that sit more than they’re driven do not heat up the pads regularly, which causes rust to form and cause rust to separate the pad from its backing. The first symptom is often a spongy pedal. But many consumers don’t notice the symptom, because it presents gradually.
“They think it’s a normal thing with their vehicle, because it came on slowly. It’s always a good idea to do a road test, even if you’re not planning a brake job, to see what the brakes are like, to see if there is a problem with them and alert the customer.”