Skip the auto shop - Our mechanics make house calls

Q: Brakes go to floor

asked by on

I hear a hissing noise when brake pedal is depressed and slowly goes to floor and does not stop truck. But when I depess it fast it works as before. Master cylinder-no leaks. What do you think?

My car has 70000 miles.
My car has a manual transmission.

One of the most common causes of the brake pedal going to the floor is a loss of brake fluid. Generally, this is easy to detect due to the fact that there is usually brake fluid leaking on the ground underneath the vehicle. The brake booster is a mechanism that uses vacuum pressure to take the force being applied to the brake pedal and amplify it. If the booster is bad, then the full amount of force needed to activate the master cylinder and pressurize the brake fluid isn’t going to be there.

Another possible cause for this may be a failing master cylinder. The master cylinder is where the brake fluid is compressed creating the necessary hydraulic pressure the braking system needs in order for it to stop your vehicle. When the master cylinder fails, this may cause a loss of hydraulic pressure which will usually also cause the brake pedal to go to the floor. I would recommend having an expert from YourMechanic come to your location to diagnose your braking system.

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: When i turn left i here a poping noise. When i brake i hear a popping noise. When i hit a bump the whole front end shakes.

Given your mileage, and the symptoms you describe, it is likely your ball joints, both upper and lower, are toast. Potholes, braking, and turns cause the worn joints to move out of position, causing the behavior you describe. For lower...

Q: When looking at the Truck Engine my fan spins to the left which way would I turn the bolt to loosen it on a fan clutch

Always loosen the fan in the same direction it turns. You may need to have the holder and large wrench. You may need to shock the fan to the left while holding the fan pulley. I usually leave the belt...

Q: Radiator is leaking

Hello. When a radiator is leaking, it is an issue which requires immediate attention. If you continue to drive under this condition, you will be running the risk of damaging other cooling system parts and ultimately, this could become very...

Related articles

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...
P0240 OBD-II Trouble Code: Turbocharger Boost Sensor B Circuit Range/Performance
P0240 code definition Turbocharger Boost Sensor B Circuit Range/Performance What the P0240 code means P0240 is an OBD-II generic code triggered when the Engine Control Module (ECM) detects the intake boost...
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...