Skip the auto shop - Our mechanics make house calls

Q: Master cylinder losing fluid and I can't find leak.

asked by on

Brake fluid is leaking even though I cannot see the leak. The brake fluid in the master cylinder drops every few days and keeps the "brake" light on.

A: It is possible that your brake fluid could ...

It is possible that your brake fluid could be leaking into the power brake booster. This is the big round container that the master cylinder is bolted to. The brake booster operates off of the vacuum created by the engine to increase the amount of pressure that can be applied to the master cylinder with your foot. If a seal has failed in the back of your master cylinder it is possible for the fluid to be sucked into the booster. This would create a non visible leak without further inspection. I would suggest you enlist the help of a mechanic to check your brake hydraulic system for leaks to confirm where the brake fluid is going.

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: engine misfire on running temperature

This sounds like you may have potentially two unrelated problems. The first may be related to the issue of timing causing the misfiring, and the second could be related to the fan running more than usual. First, the misfiring...

Q: How far can you drive your car if you need a catalytic converter

Hi there. It's very common for a bad or failing catalytic converter to cause multiple engine performance issues ranging from sluggish performance to potentially damaging seals and other internal engine components. It's very difficult to tell you exactly how...

Q: Why are my strut mounts failing

The shoulder on aftermarket struts at the top of the piston is sometimes designed such that you have to put a washer or washers underneath the strut retaining nut in order to properly tighten the piston to the mount. Also,...

Related articles

What Causes Hoses to Leak?
While the largest part of your engine is mechanical, hydraulics plays a significant role. You’ll find fluids at work in a number of different areas. Your car's fluids include: Engine oil Transmission...
How to Avoid Back Pain in a Car
If you have back problems, sitting in a car for an extended period of time can be excruciating. Even without back problems, you could experience discomfort and soreness from...
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...