While driving the other day, all was fine. Suddenly the pedal goes to the floor! I pull over using the hand brake. I fool around in a open parking lot and the problem persist momentarily then suddenly dissappears. Now the brakes seem fine.

After limping home (with no more problems) I can see no obvious issues (i.e. plenty of brake fluid, no leaks or wetness anywhere including the m/c). Although, I am probably over due in replacing the brake fluid.

Also, when I say the pedal went to the floor, it wasn't like I was stepping on air, but my braking power probably went down to about 25%.

Clearly it is time for some brake work, but how much and where to start? Is it possible for the m/c to fail intermittently?

signed lucky

my guesses:
either air in the system, sticky pistons or the MC is on it's way out ...

Andy

Hmmm interesting and scary puzzle.....

1) Pedal went to the floor just once and it works now and before.
2) The handbrake was able to actuate the inner piston on at least one rear caliper.
3) You're overdue for a fluid change.
4) No obvious leaks

I have two guesses:

1) Some crud got into a seal in the MC. This allowed the fluid to bypass and caused the pedal to go to the floor. The crud cleared and now the system works again. Could also have happened with just a bad seal that is on its way out.

2) There really is a leak and you just didn't find it. I don't like this answer that much since the leak would have to have been temporary since the brakes work now....

I'm betting that MC is ready for a good reconnoiter.

Air. Bleed the system. Air bubbles do tricks like that. Doesn't cost anything to check it out.
Refer to the proper wheels to begin with and work toward the front ending bleeding of the brakes at the wheel nearest the master cylinder. See Pelican site for the proper technique.

Cooley

Replace your master cylinder. I had a friend roll his fully restored (interior was in for 8 hours) 60s Volvo PV544 down a cliff because the master cylinder went out. If the brakes were working fine and feeling fine and then magically disappeared, then I'd go directly to the master cylinder.

From my experience, I would ask if you have rubber lines and how old are they. If they are old (5 years or more) or you don't remember having changed them, or never have changed them, then do that. I have had the same experience you've described and what happened is you applied the brakes pushing the fluid to the calipers. But the fluid ain't returning and pressure remains in the caliper pressing against the rotor. Result; boiling in the caliper! No brakes! Multiple applications of the brake pedal may ease the situation for the moment, but it will be back.
Everyone who drives any car should walk around the car and place their hands on the hubs. If they are hot to the touch, you have a problem. Common problem with all cars that sit for a long time. Never had a problem with the M/C. Always the lines.
Don

Thanks all.

I have rubber lines on front and braided on rear (don't ask.....). I will start there and then move directly to the m/c. It has never been rebuilt so......as soon as I finish all my other projects I'll do that.

Ah...now I get wrestle with 17 vs 19mm......I luv my car

thanks again

JR

Dont rebuild master cylinders. Replace them.

I'm going to lean towards sixerdons recomendation. It sounds like you are getting ready to lose a rubber line.


B

Thanks Brad. So lines first.


JR

WARNING - NPC
Brakes/No Brakes/Brakes reminds me of a problem my sister had years ago with a Plymouth Horizon. In the driveway, the brakes were fine, but drive for a while, and the brake pedal would go to the floor when trying to stop. Pump them up, and they would work fine for a while, then the problem would occur again. Her husband and I replaced the master cylinder, and the problem continued. Bled several quarts of fluid through the system, still the same. Figured maybe we got a bad master cylinder, so replaced it again, and bled a lot more clean fluid through the system. Still didn't fix the probelm Gave up and took it to a mechanic who worked on it for a couple of days, finally found that an exhaust leak was blowing on one of the rubber brake lines. After driving a while it heated things up and no brakes. Pump the pedal a bit and the fluid and line cooled down and the brakes worked again. Replaced the exhaust pipe and cleared up the brake problem.

Harvey