Brake pedal goes soft after holding for awhile?

[Laviathan222]

So heres the dealio.... Say im sitting at a stop light on a hill holding the brake its regular... but then occasionally it will just start to go toward the floor losing brake power then i have to pump the brakes and it goes back to its regular point when depressed.... ive checked my brake fluid and its full so there cant be a leak... master cylinder?

[deevergote]

The master cylinder is most often an internal leak. You won't see anything under the dash. Leaking fluid under the dash is more often associated with a failing clutch master cylinder.
Unless you've somehow allowed air into your brake system, it's pretty much guaranteed that a sinking brake pedal is due to a failing master cylinder.

[dj_ender]

The master cylinder is most often an internal leak. You won't see anything under the dash. Leaking fluid under the dash is more often associated with a failing clutch master cylinder.
Unless you've somehow allowed air into your brake system, it's pretty much guaranteed that a sinking brake pedal is due to a failing master cylinder.

Damn it, I'm long overdue for sleep, mixing up clutch master cylinders and brake master cylinders....

[deevergote]

It's 3am here... and I just won at scrabble. Sharp as a tack!

[dj_ender]

It's 3am here... and I just won at scrabble. Sharp as a tack!

You seem to keep odd hours Mike.

[SOHC-FTW]

it's 3am Here... And I Just Won At Scrabble. Sharp As A Tack!

Lmao.

[Laviathan222]

im overdue in sleep category as well... haha! the odd thing is it's not leaking any break fluid, if it were the reservoir magically keeps refilling itself... this is what puzzles me, could they just need to be bled? i haven't done anything with the brakes, so maybe the idiot that owned it before me hadn't a clue what he was doing... well i actually know he hadn't a clue cause he pointed at the distributor and said he replaced the alternator... haha

[dj_ender]

im overdue in sleep category as well... haha! the odd thing is it's not leaking any break fluid, if it were the reservoir magically keeps refilling itself... this is what puzzles me, could they just need to be bled? i haven't done anything with the brakes, so maybe the idiot that owned it before me hadn't a clue what he was doing... well i actually know he hadn't a clue cause he pointed at the distributor and said he replaced the alternator... haha

Highly doubt it my friend. I have had the same issue in 2 cars, BOTH where a failed master cylinder.

[Laviathan222]

erm.... wait what do you mean by internal leak?

[quaidum]

erm.... wait what do you mean by internal leak?

the fluid passes by the seal(making it a non-pressurized system) without escaping the actual cylinder

[deevergote]

Exactly. The master cylinder creates pressure with a plunger. Hydraulic fluid doesn't compress, so it forces the brakes to clamp down. When there's an internal leak, the fluid seeps past the plunger, resulting in a loss of clamping force at the brakes.

[Laviathan222]

Exactly. The master cylinder creates pressure with a plunger. Hydraulic fluid doesn't compress, so it forces the brakes to clamp down. When there's an internal leak, the fluid seeps past the plunger, resulting in a loss of clamping force at the brakes.

Thank you! Precisely what i was looking for!

... A leak....that is internal...not external.

Not what i was looking for...

[dj_ender]

Not what i was looking for...

I tend to give people what they don't want to hear.

[deevergote]

If someone else posted as you did, would you have banned them for flaming?

[dj_ender]

If someone else posted as you did, would you have banned them for flaming?

possibly....point taken.