is it the master cylinder?

[hutch]

i put bigger tires on my truck and took it out for a test drive and it was working fine. the block before i got home i tested the brakes and was pushing down hard on the pedal. they were working then but as soon as i pulled into my driveway i lost all pressure in the pedal. i opened the hood and noticed at the front of the master cylinder it was wet with brake fluid. my dad pumped the brakes while i looked for a leak but i couldn't find anything. with the truck off/in accessory mode the brakes work but as soon as it gets turned on it loses all pressure. is my master cylinder bad or is it something else?

 

[Ranger44]

Try a quick test.

With the truck off, pump the pedal till it is hard. Hold the pedal and start your truck. It should sink slightly. This will eliminate the vacuum booster.

Either way, fluid leaking isn't necessarily a good thing.

 

[hutch]

alright i tried pumping the pedal but it was consistently the same pressure. it never got really hard to push down. does that mean its something with the vacuum booster?

 

[Ranger44]

If it didn't sink when the truck was started then it's a sign of a bad booster.

The fact that you said the pedal never built up pressure, makes me think that there's a leak somewhere>>>

 

[hutch]

the pedal did sink when the truck was started but the pedal never got really hard to push down while the truck was off. i've checked for leaks while my dad pumped the pedal but i havent been able to find anything and the fluid has stayed a consistent level through about 15 minutes of pumping the pedal and looking for leaks. the only time i noticed it being wet was when i initially lost pressure the first time. the front of the master cylinder was wet. but since then i havent been able to find any leaks.

 

[hutch]

i replaced the master cylinder and the brakes are working again. thanks for the advice tho ranger 44

 

[Ranger44]

Yeah, with fluid leaking around the master cylinder, it would have been the most probable cause. Always willing to help out any way I can.

Glad you got it fixed!