Skip the auto shop - Our mechanics make house calls

Q: Brake pedal sinks all the way to floorboard

asked by on

While pulling a load, the brake pedal began to sink all the way to the floor. I replaced the front calipers, master cylinder, and new pads all around. Also, several times I bled the system. When the car is off, the pedal feels very firm. When I start my car at idle, I have a good feel in the brake pedal, but when I begin to drive a couple of feet and then stop, the pedal sinks almost to the floorboard. A boost test was done and it was good. My car previously had a 2007 Is2 corvette v8 swap, no ABS, and has braided brake lines as an upgrade. It also has disc brakes all around. Would a bad check valve be the cause of the brake pedal problem or do you think the motor is causing too much vacuum?

Hi. Sounds like a sweet setup you have there for your 1998 Nissan 240SX. It sounds to me like the lack of brake pedal pressure could be due to a leaking brake booster possibly or a brake booster hose collapsing under vacuum. I would suggest that you have the brake booster smoke tested for leaks to monitor the brake booster hose while the brake pedal is operating to verify that it keeps its proper shape without collapsing under pressure. Have a certified technician inspect your brake system to let you know exactly what repairs should be done.

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

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: Brake failure every two months; calipers/brake lines have to be repaired

Hello. Depending on what exactly needs to be repaired on the brakes would help me determine what the actual issue is. If you are consistently having the same brake failure than that does tell me that there is a larger...

Q: Oil steam exhaust pipe

After your comment about flooding the parking lot with steam, this symptom leads me to believe you may have a failed head gasket. A failure in this seal will allow coolant to leak into the combustion chamber once the cooling...

Q: Air con isnt getting cold

Hello. You likely need to [pressurize the refrigerant]https://www.yourmechanic.com/services/heating-ac-inspection) in the system properly. Unfortunately there is no way to test the system without hooking up gauges and physically testing it. If you have recently filled the system, there may be a...

Related articles

How Do Power Car Windows Increase Passenger Safety?
Power windows are responsible for approximately 2,000 emergency room visits every year. When a power window closes, it exerts enough force to bruise or break bones, crush fingers, or restrict an airway. Though...
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...
P2103 OBD-II Trouble Code: Throttle Actuator Control Motor Circuit High
P2103 means there is a fault with the throttle actuator control motor circuit, likely due to a defective electrical component or part.