So I'm having a brake issue:

One day coming off the freeway my brake pedal randomly went limp, all the way down to the floor, barely made the stop. Resevoir was just about topped off at this time. Have had the car for a year, has never had problems with brakes.

I bled the system, (multiple times since) thinking it was just air in the system. 3 of the 4 lines bled well, but front drivers side does not bleed at all using gravity method, and only with the two person method.

My neighbor thinks it's a failing master cylinder, but the cylinder isn't leaking from what I can tell. No level drops in over 2 weeks.
I also hear and see air coming back up into the master cylinder in the form of air and like a push of liquid upwards,.
Anyone have any thoughts or ideas?

 

Hey,

Curious, did you get this resolved and if so, what was the solution?

Michael

 

Oh yeah, I forgot to update the post.
So it turned out to be the brake master cylinder failing, so I replaced it.
I thought it might be the brake booster at first but my neighbor said to just do the master cylinder first, and if it didn't fix it, THEN replace the brake booster.
I fully bled the system after install, and the car felt amazing afterwards.
Was relatively straightforward as well, just use some rags to avoid spilling any fluid on your paint or in the bay.

 

...and to note, as you discovered, mc does not need to leak externally to be bad. It can leak internally, where its just not pushing enough fluid to the calipers. Fluid leaks past piston and back into reservoir.

You can generate well over 1,000 psi in a brake hydraulic system. If the seals aren't great, that much pressure will leak past them, back into reservoir.

Point being don't rule out mc issue just because there is no visible external leaks.

 

@Car Anology,

Did you mean to send this reply to this message? I think there was another user with brake bleeding issues.

Michael