Your braking system is a complex series of components that handles some of the strongest physical forces you can throw at your car on a daily basis. The series of hydraulic, mechanical, and electronic parts that extend from your brake pedal to your lug nuts needs to function perfectly every time you put your foot down to keep you from sliding through the neighborhood stop sign.
Most drivers are familiar with some of the tell-tale signs of a brake system that is starting to show its age. After all, some components in your braking system, such as brake pads, brake rotors, shoes, and drums (even the brake fluid itself) are designed to wear down over time. They are consumable items, and keeping a close eye on their condition will help you maintain your car’s braking performance at its peak. A soft pedal, poor stopping distances, and squeals from the wheel wells are all indications that some part of your brakes need a little attention.
Other parts of the braking system generally are meant to last the lifetime of the vehicle, such as brake master cylinders, brake lines, anti-lock braking (ABS) components, brake boosters, and brake calipers. Among these tougher mechanisms, brake calipers live the hardest life. They are subjected to high temperatures, corrosion from chemicals and road grime, moisture, and rust. While fairly simple and robust in their construction and operation, and usually long-lasting, calipers can succumb to these harsh conditions over time. However, it’s not always crystal clear when you might be on the threshold of caliper failure.
What Does It Do?
A brake caliper transfers the hydraulic force created through the brake fluid via the brake pedal and the master cylinder, into mechanical braking force. The brake fluid pushes the caliper pistons outward from the caliper itself, which then squeeze the brake pads against the rotor, (hopefully!) slowing the vehicle.
In some ways, the brake caliper is the lynchpin of the braking system – where hydraulic pressure that starts at the end of your big toe is finally transformed into braking force. Historically cast from ductile iron, many manufacturers are now moving to aluminum calipers. These save weight and can have higher resistance to corrosion. Nearly all commonly found brake calipers only have one significant moving part – the caliper pistons themselves.
How Do They Go Wrong?
Because of their important role in keeping you on the road, and the heavy forces they must endure stop after stop, brake calipers tend to be over-engineered for their application. But any automotive component with moving parts and fluids can be vulnerable to failure. How can you assess the condition of your calipers?
The best way to get an idea about how your calipers are doing is simply with a visual inspection. Jacking up your vehicle (always remembering to place it on jack stands when you’re working under a car), removing a wheel, and simply getting a good look at the thing will tell you a lot. If you turn the steering wheel in the opposite direction from the brake you’re working on, you can get a more complete view of the caliper.
What you are looking for here are four things: brake fluid leaks, uneven brake pad wear, excessive corrosion, and missing or deteriorated caliper piston seals.
For obvious reasons, any leaking brake fluid will need to be addressed immediately – often leaks will come from the brake lines, but a common source of leaks is also where the brake line threads into the caliper itself. On my older Range Rover, the front calipers each have two brake lines feeding it, and the upper ones always seem to develop leaks. Leaks in this area can indicate a problem with the brake line, but it can also happen due to a cross-threaded fitting in the caliper, or a crack in the cast iron, both of which are pretty rare, but neither of are what you want to see.
If one of your brake pads seems to be wearing down faster than the other, this is an indication that you have either weak or uneven pressure being applied by the caliper to the brake pads. This can be because of fluid leaks, dirt gumming up the pistons, or corrosion.
Regarding corrosion, a lot of cast iron calipers that look pretty crusty on the outside, even completely rusty, will still perform just fine. But, over time, corrosion may allow moisture to penetrate the internals of the caliper, and may affect caliper mounting surfaces and fixtures. Since brake fluid absorbs water, and in doing so loses its effectiveness, any ingress of moisture will negatively affect the entire braking system.
Lastly, the pistons ride on a rubber (or sometimes metal and rubber) seal as they expand and retract from the caliper. These seals can be cracked, crumbling, or even missing entirely – again allowing moisture and contaminants into the caliper body itself. Grit and grime can score the smooth outer surface of the piston, which only exacerbates the problem. Corroded calipers can, in the worst case scenario, stick in place or freeze up altogether.
There are a couple of ways to evaluate your calipers’ performance from the behind the wheel as well. However, before you jump to conclusions about failing calipers from these symptoms, perform that visual inspection, because most of these may indicate a problem with other brake components as well.
Leaky, stuck, or partially frozen calipers can create uneven braking force – locking up the rear brakes prematurely, or pulling to one side or another under braking. This can be due to pad wear as well, so check those pads out first. Scratching or squealing noises can also suggest that you’ve got some contamination or corrosion in the caliper as well, particularly if you hear these sounds when first applying the brake pedal.
Working on your own brakes may seem a little daunting – after all, in concert with your tires, they are the front-line safety system for your vehicle.
But, should you find they need replacing, brake calipers on most vehicles are tied to the wheel hub with only two bolts and a brake line, and they are simple devices internally. So, their removal and installation is straightforward (disregarding any serious rust issues). Old calipers can be cleaned thoroughly and rebuilt with new seals, pistons, and bolts, and maybe even an eye-catching shot of high-temperature paint.
Making the jump to new calipers is a bolt-on affair as well. In either case, you’ll need to flush, fill, and bleed your entire braking system with fresh brake fluid and install new brake pads (always a safe and cost-effective idea when rebuilding or replacing brake calipers).
Have you ever had a brake caliper seize up on you? Questions about refreshing your brake system? Let us know down in the comments.