Q: Brake sinks slowly while at stop

asked by on October 28, 2016

96 Honda Accord EX V6. Brake pedal sinks slowly all the way to floor while at a complete stop. Usually takes about 10-15 seconds for Pedal to be completely at floor, with absolutely no pressure and car starts moving. When this occurs, I can pump brake pedal which takes pedal slightly back up, but once I leave constant pressure again, sinking starts again. There are FEW times I've driven the car WITHOUT this occurring, but cannot conclude what factors were present at the time (i.e.; outside temp, car haven't been driven in a few days). Except that it almost always happens when A/C is on vs off. More info: NO problems with brakes when depressing while driving, no longer than usual stopping distance, not spongy otherwise. Checked brake fluid (normal). And NO brake fluid leaks found undercar at all. Braking power is perfectly fine while normally depressing pedal as you would when coming to a stop. Older car with unusually low mileage. What could this be?

My car has 970000 miles.
My car has an automatic transmission.

The most common cause for the brake pedal to sink slowly to the floor will be the brake master cylinder internal pressure cup failure. The seals may be worn or sludged up from old dirty brake fluid.

I have seen where brake pads were replaced and when the caliper is pushed back with the bleeder valve closed will push dirty brake fluid back into the brake master cylinder and then when the brake pedal is pumped up the debris get into the master cylinder rubber piston cups causing them to not seal any more.

The fix would be to flush out the entire brake system with fresh brake fluid [https://www.yourmechanic.com/services/brake-system-flush] then replace the brake master cylinder with a new one and bleed and flush the system out completely. A certified professional from YourMechanic can come to your car’s location to inspect the sinking brakes so that this gets repaired correctly.

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Fair and transparent pricing


Experienced Mechanic?

Earn up to $70/hr

What others are asking

What is the satellite radio electronic serial number on the SIRIUS Radio and why is it necessary?
Your SIRIUS Radio is equipped with a unique identifying number, called the satellite radio electronic serial number, or ESN. The ESN is used to identify your radio when applying for SIRIUS Radio service. It’s a 12-digit number and you must...
How do I express-open or express-close the power sunroof?
The power sunroof has an express feature that allows you to open or close it without holding down the button. Here’s how. 1. Locate the power sunroof controls, which are on the overhead console. 2. Find the open and close...
Short in car
Without knowing what sort of problems are occurring with your car it will be hard for me to help you. From my experience with this vehicle the most common shorts occur at the fuse box. The other common electrical issues...
My radio has power but is not turning on
Hello there. A few different faults can cause the radio to cut off like this when it is powered up. The most common would be a voltage spike from when it was plugged in. Other potential issues include a shorted...
Engine losing power, gas pedal unresonsive
Hello there, a few common faults can cause these type of symptoms. The most common would be the vehicle going into limp mode, a fuel pump (https://www.yourmechanic.com/services/fuel-pump-replacement) problem, bad spark plugs (https://www.yourmechanic.com/services/spark-plugs-replacement), faulty MAF sensor (https://www.yourmechanic.com/services/mass-airflow-sensor-replacement), a vacuum leak, or...
Regularly maintenanced car has progressive power loss - 1997 Toyota Supra
Check the basics - check compression and engine tune. Check for a dirty air filter (https://www.yourmechanic.com/services/air-filter-is-clogged-inspection), dirty fuel filter (https://www.yourmechanic.com/services/fuel-filter-replacement), proper fuel pressure (https://www.yourmechanic.com/services/fuel-pressure-regulator-replacement), clogged exhaust or catalytic converter (https://www.yourmechanic.com/services/catalytic-converter-replacement). A YourMechanic professional can help with the diagnosis of your...
Low idle when stopped unless the a/c is on or i shift into neutral
Due to the change in load put on the motor when shifting into gear vs neutral and the change in load when the a/c is on vs not on, this may suggest you have a bad MAP sensor. Both of...
I was driving to work in a lot of rain and my windshield wipers just stopped in the middle of my windshield. Any ideas what it ma
The windshield wiper system uses a small electric motor to move the wiper arms that you see on the windshield. That electric motor is controlled through a switch, relay, fuse, and wiring. One, or more, of those electrical components has...
Would a bad or faulty vvt solenoid cause the engine to knock and cause a misfire on the
Hello there. A bad or faulty connected VVT solenoid can and often does cause engine knocking, inconsistent idle and acceleration problems. The issue could be with the solenoid itself or the electrical harness connected to the VVT. The best way...

Related articles

The Best Used Cars to Buy For a Graduation Gift
Your Your little bundle of joy has grown up and on the cusp of entering adulthood. Graduating is a milestone, and you want to reward their hard work and show how proud you are. Buying a used car is a...
Symptoms of a Bad or Failing Brake Hose
If your car's brake pedal feels mushy, the brake hose looks damaged, or if your brakes stop working, you may need to replace the brake hose.
The Top 5 Selling Cars in Georgia in 2012
Georgia Georgia offers drivers a mild climate with very little snow, but rain is a major factor. Previous best-selling cars in the area, such as the Escape, Fusion and Camry, have shown that residents prefer a mix of both SUV...