Skip the auto shop - Our mechanics make house calls

Q: Brake sinks slowly while at stop

asked by on

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.

A: The most common cause for the brake pedal t...

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.

Was this answer helpful?

Need advice from certified mechanic? Get help now!

Over 1000 mechanics are ready to answer your question.
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Ask a Mechanic
(100% Free)

Have a car question? Get free advice from our top-rated mechanics.

Ask A Mechanic
Over 10,000 questions answered!

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Save up to 30%

Get a quote

What others are asking

Q: Water in the break fluid.

Hello! The quick answer is yes we can get the water out. If you did not push on your brakes yet, then the water may not of made it past the brake master cylinder. The master cylinder would need to...

Q: VTC activator rattle on a 2006 Honda Civic Sport

Basically, those systems get full of crud a lot of times. First, take all the parts off the outside. Clean out the valve assembly and the filter screen. Sometimes it is as simple as one of the gaskets leaking...

Q: When I start my car up its a rattleing sound was thinking catalytic

Hello, the catalytic convertor can make that type of noise. Inside the convertor is a honey comb shaped element that the exhaust gases pass through. Part of that element can fracture and become loose within the shell of the convertor,...

Related articles

How Long Does a Distributor O Ring Last?
The distributor is part of the ignition system in your vehicle and its purpose is to route high voltage from the ignition coil to the spark plug. The spark plug then...
How Long Does a Heater Control Valve Last?
Keeping the right amount of coolant in a car is essential in keeping the engine at the right temperature. Failing to have the right amount of coolant or even bad elements...
P0052 OBD-II Trouble Code: HO2S Heater Control Circuit High (Bank 2 Sensor 1)
P0052 code definition HO2S Heater Control Circuit High (Bank 2 Sensor 1) What the P0052 code means This code is seen when the Engine Control Module (ECM) tries to control the...