Statistics have shown that soft brakes constitute a hazard to both you and other road users as they make slowing down your car (and stopping) much harder. So, naturally, if your brake pedal has to reach the floor before your vehicle slows down, then you shouldn’t be driving that car.
Ideally, your brake pedal should be tight and very responsive. However, sometimes they may go soft and become ineffective in getting your car to slow down.
But what causes your brake pedal to sink to the floor of your car when you press it?
Keep reading to find out.
Table of Contents
- Major Reasons Your Brake Pedal May Go Soft
- Diagnosing and Fixing the Problem
- Why Does My Brake Pedal Go to the Floor When I Start My Car?
- How Do You Know If the Master Cylinder is Bad?
- How Do I Know If My Brake Booster or Master Cylinder is Bad?
- Why Does My Brake Pedal go to the floor after bleeding?
Major Reasons Your Brake Pedal May Go Soft
In the following paragraphs, we explore several causes of a spongy brake pedal.
Air in Brake Lines
If there is air in your brake lines, you’d typically not experience a strong, consistent braking feel when stepping on your brake pedal. This is because air is compressible, unlike brake fluid, which is not.
So, if you notice you’re running low on brake fluid, top it off as soon as you can. Then, bleed the lines to be on the safe side.
Otherwise, without brake fluid, you’ll likely not be able to stop your car until you hit something.
Internal Seal Failure in the Master Cylinder
If there is an internal seal failure in your master cylinder, your brake lines will take in air every time you apply your brakes. If this continues, it can eventually cause your brakes to fail, which is not something you want.
Thankfully, you can quickly test the internal seal of your master cylinder by blocking off the ports on the master cylinder while using a pressure gauge to measure the pressure in the system upon brake application.
This usually happens when driving on heavy slopes or after repeated heavy brake applications. In such a scenario, a brake fade may occur when your braking system becomes too hot, which causes your brake fluid to boil or your brake pads to overheat.
When this happens, your brakes become progressively less effective. The only fix is to replace both your brake fluid and pads.
Bad Brake Booster
Does your brake pedal sink to the floor but still manages to stop your car? Then your brake power booster may be the culprit.
Your brake power booster ensures that you don’t have to expend so much energy when applying your brakes to slow down your car. By using a vacuum line to overcome fluid pressure in your brake system, the brake power booster helps to manage energy consumption.
However, when the booster becomes faulty, you will find that your stopping distance increases and your pedal starts sinking to the floor.
Low Brake Fluid Level
The good news with low brake fluid levels is that a warning light will likely appear on your dashboard. So, once you see your brake fluid warning light on, it’s time to check your brake fluid.
However, if your brake fluid gets low enough that air enters your braking system, it may not be enough to top up the fluid. You’d also need to bleed the lines.
Diagnosing and Fixing the Problem
By now, you have some insight into the possible reasons your brake pedal may become soft. But, how do you identify the specific reason your brake pedal is sinking to the floor. Here are tips on how to diagnose vehicle brake problems:
Check Brake Lines and Calipers
The first step is to check your brake fluid level. A full brake fluid means there is no leak in your brake lines. However, if the level has gone down drastically, there is likely a leak.
In this case, you’ll need to examine the brake lines from all your four wheels to identify where the leak is.
Pro Tip? Make sure to check the wheel cylinder seal and caliper.
Bleed the Brakes
Soft or spongy brakes may mean there is some air in your brake lines. In this case, bleeding the brake lines can quickly solve the problem. But, make sure air does not get into the ABS module as this can be very tricky to bleed!
Replace Brake Pads
Heavy braking or large hills can quickly wear out your brake pads, leading to a soft brake pedal. In this case, you’ll need to replace your brake pads.
If you drive at high speeds or on very hilly terrain, investing in brake pads that can withstand higher temperatures may be more appropriate. However, sport brake pads may be less than adequate for emergency stops at low street speeds when the pads are much colder.
Check the Brake Master Cylinder
Wear and tear can cause the seals of your brake master cylinder to become faulty and develop leaks. If this happens, the best solution is to completely replace the brake master cylinder.
Remember, don’t try to drive your vehicle if the brake master cylinder is leaking, as your braking system will not work correctly. Instead, replace the unit or contact a professional to help you resolve the issue.
Check Your Brake Rotors
Your brake rotors may sometimes be the problem, or they can give you a hint about the issue. Thankfully, you can usually examine your brake rotors without having to remove your wheels.
Are there grooves in the rotors? Are your brake pads unevenly distributed along the surface of the rotor? Can you see brake fluid leakage around your wheels?
Finding the answers to these questions may give you a final clue as to why your brake pedal goes to the floor when you press it.
Why Does My Brake Pedal Go to the Floor When I Start My Car?
More often than not, a low brake fluid level, a leaking master brake cylinder, or a faulty brake booster may be why your brake pedal sinks to the floor.
How Do You Know If the Master Cylinder is Bad?
Simply remove the vacuum hose on the brake booster. If the brake pedal still drops to the floor, the master brake cylinder is likely faulty. Otherwise, the brake lines may be leaking. But, of course, you’d have to inspect the gasket visually to know for sure.
How Do I Know If My Brake Booster or Master Cylinder is Bad?
First, disconnect the vacuum hose attached to the brake booster. If your brake is hard when you press it, then the brake booster is likely the culprit. However, if the brake still sinks to the floor, then your master brake cylinder is most likely faulty.
Why Does My Brake Pedal go to the floor after bleeding?
If your brake pedal is still spongy after bleeding, you may not have carried out the procedure correctly. Before releasing the brake pedal, ensure you tighten the air bleed screws. Otherwise, air will enter the braking system before you can close the bleed valve.