On any given car ride, you step on the brake pedal dozens, if not hundreds, of times. Every time you do, the force you put on the brakes is instantly boosted and transmitted to the brake calipers or wheel cylinders, slowing or stopping your car. If you have a soft brake pedal (sometimes described as spongy brake pedal), what is it telling you about your brakes? Should you be concerned?
If there are problems with the brake fluid, master cylinder, wheel cylinders, brake calipers, or brake lines and hoses, this could result in a spongy brake pedal and possibly a dangerous situation. Here’s a quick guide to diagnose and repair your soft brake pedal and keep your ride and your loved ones safe.
By far, the most common cause of a soft brake pedal is air in the system. The brake system functions as well as it does because brake fluid is incompressible, so it transmits 100 percent of the force to the four brakes. Air, on the other hand, is compressible, transmitting almost no force to the brakes. When you step on the brakes, your foot compresses the air first, which takes time and results in delayed or reduced braking on one or more wheels.
Fortunately, the fix is simple. Bleeding the brake system will flush out any air bubbles in the system. Make sure the brake fluid lever in the master cylinder reservoir never drops below the “LOW” mark. If air entry recurs, you may have a more serious problem. Air may be pulling in past a caliper piston seal or master cylinder seal.
Slightly less common, but especially dangerous, can be improper repair practices. Replacing a hard brake line with anything but another hard brake line is asking for trouble. Not only will you have a spongy brake pedal, you risk bursting the line and losing all braking capability. Luckily it isn’t too hard to replace a hard brake line, so there’s excuse for not doing it right. Pre-bent brake lines are often available, but there are also options for bending your own complete with pre-formed flares.
Somewhat less common and harder to recognize are brake mechanical problems. Aside from the hydraulic system involving pistons, seals, tubing and hoses, there are a number of mechanical parts in the brake system: brake rotors, drums, calipers, pads, cages and carriers. The most common mechanical failure is seized brake caliper sliders. If one of the sliders seizes up or a brake pad hangs up, the caliper will only apply pressure on one end of the pad. The binding slider or stuck pad springs back, making it feel just like air in the brake lines or any other failure.
The fix for this kind of spongy brake pedal can be a little more complicated. You’ll have to take apart the brakes, making sure that all pads and sliders are moving freely. Heavily-corroded brakes, sliders or cages may require replacement or major repairs to put them back in order.
Pro Tip: Anti-seize is not a lubricant, and petroleum-based grease does not have the temperature resistance needed. Use only heavy silicone grease on the sliders and make sure the dust boots are in place.
A soft brake pedal can increase braking distance, which can make stopping in an emergency situation dangerous. Fortunately, with some time, you can take care of it on your own and get back to driving.
Check out all the brake system products available on NAPA Online or trust one of our 17,000 NAPA AutoCare locations for routine maintenance and repairs. For more information on diagnosing or repairing a soft brake pedal, chat with a knowledgeable expert at your local NAPA AUTO PARTS store.
Photo courtesy of Wikimedia Commons.
Ben has been taking things apart since he was 5, and putting them back together again since he was 8. After dabbling in DIY repairs at home and on the farm, he found his calling in the CGCC Automobile Repair program. After he held his ASE CMAT for 10 years, Ben decided he needed a change. Now, he writes on automotive topics across the web and around the world, including new automotive technology, transportation legislation, emissions, fuel economy and auto repair.