Regardless of the cause, there's no `acceptable tolerance' for a brake pedal that slowly sinks towards the floor. A braking system in good working order should be able to hold the brake pedal at the same level more or less indefinitely. Any sinking is bad news and is a serious safety issue.
When brakes are not as responsive as what they should be, or if the brake pedal “sinks” down to the floor, this is a possible indication of a braking system leak. It could be a brake fluid leak, or a brake hose air leak.
You should never drive with a brake problem. That “brake pedal goes to floor,” or soft brakes situation can quickly escalate to your brakes failing. If there's been a steady drop in brake pressure or your fluid level with a side of a spongy brake pedal, assess the situation and contact your mechanic.
With power brakes, the pedal should stop 1 to 11⁄2 inches from the floor. (If you don't have power brakes, the pedal should stop more than 3 inches from the floor.) If your vehicle has power brakes and stopping seems to take excessive effort, you may need to have the power booster replaced.
There may be wear on the cylinder bore or the cup seals. Internal leaks or cup seals being bypassed must be taken into account if a car's brake pedal starts to fade toward the floor. One of the most typical signs of a cup seal failure in a master cylinder is a fading pedal without an external leak.
Is It Safe to Drive With a Spongy Brake Pedal? No. If your brake pedal feels spongy, your vehicle is not safe to drive. Identify and repair the underlying issue as quickly as possible.
Brake pedals should always feel firm when you press down. If your pedals ever feel soft and spongy, you should immediately get your vehicle inspected, as a spongy brake pedal is a symptom of failed braking components in the car.
The brake should be pulled all the way up to assure that it is set properly. If the vehicle is not set properly, gravity will force itself and the vehicle will careen down the incline.
There are only two plausible reasons for a low pedal: air in the system; and excessive movement between linings and rotors or drums (due to lack of adjustment, an out-of-round drum, or a wobbly disc that's knocking the pistons back so that there's extra space to take up before braking action begins).
Brake pedals should offer moderate resistance when pressed. If your brake pedal is going to the floor with no resistance, there is a problem. The pedal could be failing, or the problem could be as simple as a lack of brake fluid.
In nearly all cases there is no real-world performance advantage for one position over another, other than clearing the suspension and ensuring the bleed screw orientation is in the 12:00 position at or near the top of the caliper.
The reservoir should have a label that says, “full line.” If the brake liquid falls below that line, it's a sign your need to change your brake fluid or top it off. Low brake fluid can also indicate your brake pads are wearing down and need maintenance.
This can be due to a number of problems: a leak in a brake line, a loss of pressure within the master cylinder itself due to a failed seal, or air being introduced into the braking system. Your first reaction to encountering spongy brakes should be to rapidly pump the brake pedal with your foot.
The classic symptom of a failing master cylinder is a brake pedal that “dives” or sinks slowly to the floor while pedal pressure is being applied. Another sign to look out for is any leaks around the master cylinder. If a seal is worn out, it may leak past the seal and onto the pushrod that attaches to the brake pedal.
If you have an automatic gearbox, apply the handbrake first, then put it in P. This ensures that the car's weight isn't resting on the parking pawl. If you don't use the handbrake, you'll be putting constant pressure on the parking pawl and transmission components which will eventually fail, leading to costly repairs.
The most common reason for a soft brake pedal is simply air still in the system. The easiest way to diagnose this problem is to pump the brake pedal gently a few times. In doing so, the pedal should become firmer with each gentle press of the pedal.
Most brake and clutch pedals should have just a little bit of free play, usually about a centimeter, which is less than half an inch. If you feel that your free play is more generous than this, or that you don't have any at all, you'll need to adjust your pedals.
Though gentle braking is better than heavy braking, more braking is better than less. For up to the first 300 km, every time the brake pads make contact with the discs, it increases the contact surface area between the two, which leads to better braking in the long-term.
A spongy brake pedal has a slightly different feel than a soft brake pedal. Spongy brakes give the sensation that you're pushing against a spring when pressing down on the brake pedal. On the other hand, a soft brake pedal either goes to the floor or goes down too easily.
Brake Pedal Goes To the Floor
The issue may simply be air in the lines a simple fix with a cost of under $200. Or the problem might be a broken brake line, a broken caliper, or a more serious issue. This is one to have the pros handle.
YOU SHOULD REPLACE BRAKE FLUID EVERY FEW YEARS
And the best way to find out how often to change brake fluid is to follow your manufacturer's recommendations. Some manufacturers say you should replace your brake fluid every two years. Others recommend every three years, or every 45,000 miles.