brake pedal sinking

[ASTCB7]

I was driving and all if a sudden my brake pedal started sinking and I almost got into a car accident. Need help on diagnosing this problem. It's my daily and.if I need to take it to the shop tomorrow I should know now. Thanks fellas!!!

[deevergote]

It's your brake master cylinder failing. Replace it, and bleed the system properly.

[ASTCB7]

How would I know that is the problem serve? I see my fluid is still high.

[deevergote]

Serve?

Your fluid isn't going anywhere because it's in an enclosed system. You aren't leaking it externally, just internally.

[ASTCB7]

I meant deev Hahah sorry. I'll drop it off to my mechanic tomorrow where could I get a new one? Task auto?

[deevergote]

Any autoparts store should be fine.

[Bad_dude]

Buy a new one. Don't buy refurb.
Sinking pedal would only mean 3 things:
1) Air in the lines.
2) External leak.
3) Master cylinder.
It's number 3 as what you described point to it. It happens to me a few times. Use the hand brake, if you let the pedal go and brake down again fast, you'll get some brake. This is just to get you to the mechanic. Do not drive it in traffic, it would be really bad.

Good luck.

[wed3k]

lol @ "serve"

[ASTCB7]

lol @ "serve"

Typo Hahahbut hey I went out and drove my car and now my pedal seems to be fine. Breaks fine and everything, no more sinking.

Could it be I need to bleed the lines?

[Bad_dude]

Typo Hahahbut hey I went out and drove my car and now my pedal seems to be fine. Breaks fine and everything, no more sinking.

Could it be I need to bleed the lines?

That is what I would have done before replacing the MC.

[illinois_erik]

when you get into a situation like that you never want to stand on the brakes. Pump like a mofo, if a rear end of another car is coming up quick, pump like a mofo drop it into 1st and yank the e-brake in a controlled quick motion, dont just lock up the brakes tho, all while still pumping like a mofo...

[illinois_erik]

That is what I would have done before replacing the MC.

Also your fluid could be old and cruddy and has lost its hydraulic powers, when the fluids mostly water/crap and heats up, no stoppy stoppy

[deevergote]

Unless water is somehow allowed into the system, there should be no water in there. Hydraulic fluid doesn't magically turn into water. Though yes, old hydraulic fluid can be less functional than new. I'm assuming (since I have done no research on the topic at the time of this reply) that as the fluid ages, the boiling point lowers.

[illinois_erik]

Unless water is somehow allowed into the system, there should be no water in there. Hydraulic fluid doesn't magically turn into water. Though yes, old hydraulic fluid can be less functional than new. I'm assuming (since I have done no research on the topic at the time of this reply) that as the fluid ages, the boiling point lowers.

Ive been educated that brake fluid absorbs water out of the air and rubber hoses are permeable, so ancient brake fluid will probably absorb a fair amount of water just from being in service for so long thus reducing the boiling point.

[deevergote]

You have a point there.