Is the brake pedal sinking to the floor?
It can indicate critical issues, such as a brake fluid leak or a faulty master cylinder.
Ignoring it? Not an option — your vehicle won’t be safe to drive until you resolve the problem.
We’ll break down why your brake pedal goes to the floor, uncovering the root causes. More importantly, we’ll reveal how to fix the issue for a safe driving experience.
This Article Contains:
- 7 Reasons Your Brake Pedal Goes to the Floor
- How to Diagnose a Brake Pedal that Goes to the Floor
- How Do You Fix a Brake Pad that Goes to the Floor?
- 3 FAQs on Brakes
7 Reasons Your Brake Pedal Goes to the Floor
Here are the culprits behind your brake pedal issue:
1. Fluid Leaks
Pressing the brake pedal compresses the brake fluid, creating hydraulic pressure in the brake lines. This hydraulic pressure transmits force to the front and rear calipers or each wheel cylinder, which engages the brake pads or shoes, respectively.
However, a fluid leak (often from a damaged bleeder valve, brake line, or brake hose) will reduce the hydraulic pressure necessary to engage the brakes. This results in your pedal going to the floor.
2. Air in the Brake Lines
If air enters the brake lines, it compromises the hydraulic system’s ability to effectively transmit pedal pressure into hydraulic force. As air compresses more than brake fluid, you may experience a spongy pedal or more extended pedal travel (the distance the brake pedal moves when pressed.)
3. Overheated Brake Fluid
Brake fluid typically overheats from repetitive braking when you drive too aggressively or downhill. Overheated brake fluid vaporizes, causing the formation of air bubbles. When the air bubbles compress, you’ll experience extended pedal travel when braking.
4. Faulty Master Cylinder
The master cylinder is crucial for generating hydraulic pressure. When you press the brake pedal, it forces brake fluid through the master cylinder to the front and rear calipers. If the rubber seal on the master cylinder wears out, it may fail to maintain brake pressure, causing your pedal to sink.
5. Misaligned Brake Shoes or Pads
Misaligned brake shoes and pads don’t make proper contact with the brake drum or rotor. This results in uneven brake pressure when you press the pedal.
If there’s insufficient braking force on one side, the pedal will sink to the floor as the hydraulic system struggles to compensate for the imbalance.
6. Debris in the Hydraulic System
Dirt can enter the hydraulic system during the installation of new brake pads or due to a damaged brake hose. If this happens, a blockage can occur in the brake lines, inhibiting brake fluid flow. This leads to a loss of pressure and a spongy pedal.
7. Bad Brake Booster
The brake booster amplifies the force applied to the brake pedal to more effectively engage the front and rear brakes.
If its components, like the diaphragm, fail (often due to vacuum leaks as the brake boost uses engine vacuum to operate), it may not provide sufficient pressure. This results in a pedal that sinks when pressed.
Now that you know the causes of a brake pedal sinking to the floor, let’s find out which problem is responsible for your brake issue.
How to Diagnose a Brake Pedal that Goes to the Floor?
Your safety on the road depends on well-functioning brakes, so let a skilled mechanic diagnose and fix any issues.
To diagnose the root cause, your mechanic will:
- Check for warning lights: The brake warning light usually illuminates if there’s a fluid leak. For some vehicles, brake system issues can also trigger the check engine light.
- Use an OBD-II scanner: Codes like C0129 mean a low brake fluid level, which could point to a leak. DTC codes from P0555 to P0559 indicate a brake booster issue.
- Assess the brake fluid: An insufficient brake fluid level and air or dirt in the brake fluid could indicate a leak.
- Inspect the brake system: Damage to the brake lines, master cylinder, wheel cylinder, or ABS unit (ABS module) may result in brake fluid leaks. The mechanic will also check the brake shoes or pads to see if they’re in alignment.
Once the mechanic diagnoses the issue, they’ll begin fixing it.
How Do You Fix a Brake Pad that Goes to the Floor?
The mechanic will fix your brake pedal in different ways, depending on the underlying problem:
- Brake fluid leaks: They’ll replace any damaged brake lines, brake caliper seal, and in severe cases, a bad brake master cylinder.
- Air in the brake lines: The mechanic will bleed the brakes, which involves removing the old brake fluid (and air inside). They’ll open the bleeder valve and replace it with new fluid.
- Bad brake master cylinder: If the damage is minor, it might be possible to rebuild the master cylinder by replacing any damaged rubber seal and other components inside. If it’s severe, the mechanic might replace the entire master cylinder assembly.
- Misaligned brake shoes or pads: They’ll realign the brake shoes by tightening the star wheel adjuster with a brake spoon until the shoes lightly touch the drum. For brake pads, they’ll turn the adjustment screw on the caliper to push the pads closer to the rotor.
- Damaged brake booster: The mechanic may use a brake booster repair kit, but it’s more common to replace the unit.
Got more questions about your brakes?
Find the answers below.
3 FAQs on Brakes
Here’s everything else you need to know about your brakes:
1. How Do Brakes Work?
When you apply pedal pressure, it activates a piston in the brake master cylinder which creates hydraulic pressure in the brake fluid.
The pressurized brake fluid travels through each brake line to the wheel’s braking system:
- In disc brake systems, the hydraulic pressure forces the caliper piston within the brake caliper to move. The caliper piston pushes the brake pads against the spinning rotor, generating friction that slows down or stops the wheel.
- In drum brake systems, the wheel cylinder forces the brake shoes against the inner surface of the rotating drum, creating friction.
2. How Much Does It Cost to Repair Brake Issues?
The cost of repairing braking system issues varies depending on your vehicle and the specific problem.
Here are some estimates to consider:
- Bleeding brakes: $80 and $110
- Brake fluid leaks: $150 to $700
- Brake booster replacement: $200 to $1250
- Brake master cylinder replacement: $400 to $550
3. How to Prevent a Sinking Brake Pedal
To ensure a functioning brake system, you should:
- Avoid aggressive braking to prevent the brake fluid from overheating.
- Change your brake fluid every 30,000 miles.
- Tighten the brake fluid reservoir cap to prevent contamination from debris or air.
- Regularly inspect the master cylinder and brake line assembly for damage or leaks.
Brake Away from Pedal Problems with AutoNation Mobile Service
A soft brake pedal that goes to the floor is just the beginning — faulty brakes drastically increase your stopping distance, turning your car into a safety hazard. Don’t take chances; have a mechanic fix the problem ASAP and get back to driving safely.
Can’t drive to the mechanic because your brakes don’t work?
AutoNation Mobile Service will fix your brake pedal issue right from your driveway. We’re available seven days a week and provide a 12-month|12,000-mile warranty on all repairs.
Contact us for all your vehicle maintenance needs — from braking issues to engine problems and beyond.