Hello Guys,

I recently found out my breaks are sinking a little bit when the car is in idle. (only sometimes). I asked form a mechanic and he said in that case i need to replace both master cylinder and break booster.

But I asked couple of my friends, they said they had the same problem and they just replaced master cylinder.

That mechanic asked $400 just for the labor and it will cost me another $300 to $400 for the parts. I can't spend that much of money right now.
Please help me if you guys aware of this situation.

Thanks

 

Preform following:

Engine on, press brake pedal (parking brake off) and measure distance between top of pedal pad (where foot presses on) and sloped floor behind it. Should be greater then 2 3/4 inch, this is the reserve distance.

Booster test.

Engine off, press pedal several times and recheck reserve distance, should be the same.

Depress pedal and start engine, pedal should drop slightly.

Run engine for approx 2 minutes and shut off. Depress pedal slowly. Pedal should go down the furthest on first push then start to rise with 2nd and 3rd push.

Depress pedal and stop engine with pedal depressed. There should be no change in pedal reserve after 30 seconds.

If all OK above booster is OK.

For master cylinder failure, typically failure is pedal starts moving further to the floor or sometimes to the floor caused by leaking piston in the master cylinder. Also check brake fluid level.

The brakes can still work with a failed booster but of course pedal will be harder to push.

 

Thank You,

In my case pedal is not hard to push. It goes easily. And also I didn't notice any break fluid sinking too. But there's a very small oil leak in calipers.

"Booster test.
Engine off, press pedal several times and recheck reserve distance, should be the same.
Depress pedal and start engine, pedal should drop slightly."

After this step do I have to press the pedal again before I start the engine?

 

If leaking caliper, the brake system may have air.

"Depress pedal then start engine, pedal should drop slightly."

Does the pedal meet the reserve distance measurement even though easy to push?

 

"Oil" leak in the calipers equals loss of brake fluid, which equals not good. Fix your leaking brakes should be the first step. The brake system requires hydraulic pressure and leaks are not good for that.