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.

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・Fair and transparent pricing

Get a quote

What others are asking

Q: Have a brake fluid leak from a part under master cylinder, where lines from m-cylinder connect to.

In time, brake fluid degrades and absorbs moisture. It will degrade rubber components of the brake system which include the[master cylinder, front and rear brake calipers. The leak you see is from the master cylinder reservoir seals. You can just...

Q: What else could be wrong with my 1991 Honda accord

Hi there. It sounds like it may not be getting fuel. The four basic things an engine needs to run is fuel, air, spark, and timing; just remember F.A.S.T. Is there fuel in the fuel tank; the gauge could be...

Q: My speedometer miles stop moving and stayed at 34999.

This is likely a problem with the instrument gauge cluster meaning the gauge cluster itself may be bad or the transmission speed sensor may be faulty. The speed sensor reads the rotational speed of the reluctor wheel, located within the...

Related articles

Rules of the Road For Iowa Drivers
Driving on the roads requires knowledge of the rules, many of which are based on common sense and courtesy. However, even though you know the rules in...
What are the Car Pool Rules in Hawaii?
Hawaii is widely regarded as a land of vacation and relaxation, and as such, its scenic roads and routes are far better known than the state’s freeways. But, as with all...
P2428 OBD-II Trouble Code: Exhaust Gas Temperature Too High Bank 1
P2428 code definition A P2428 trouble code signifies that the PCM has detected a problem in the exhaust gas temperature sensor circuit in bank 1, which subsequently contains the number one...