Brake pedal to floor - no stop!

[JBurer]

I had the master cylinder fail on me while driving home the other day. No real warning, just foot to the floor!

Luckily, I wasn't in bad traffic or driving aggressively and was able to get the car stopped without any incidents. What surprised me was the lack of symptoms before the failure.

Have many others seen a 'no warning' failure of the brake master cylinder?
Best,
John
'91 Turbo (56k miles)

[Boxer Boy]

I took my '88 to the track for five hot laps, then decided to cool off. On the way back to the pits, the pedal went all the way to the floor. No problem, as I had already slowed way down and was cooling things off, but it was still unnerving.

Turned out the master cylinder and calipers needed an overhaul, and now all is well. There are warnings a 911 will give you if something is amiss. The trick is in interpreting those signs.

[tonythetarga]

Check your fluid level. It is possible a seal on the caliper failed and fluid leaked out giving you no pedal. m/c's will slowly fail but you can usually pump them up a bit to get the car to stop. It sounds unusual for a sudden failure unless some type of damage occured to the system. I've had a caliper seal fail while the car was sitting and found a pool of fluid by the wheel.

[RoninLB]

i've never seen or heard of a MC suddenly failing

[GaryR]

Originally Posted by RoninLB

i've never seen or heard of a MC suddenly failing

Me neither.. no massive brake fluid puddles anywhere?

[JBurer]

No "massive" loss of fluid, although there appears to be a small amount in the front trunk compartment.

From some of the searches I've done on this forum and Rennlist, it's possible for the fluid to leak past rings in the cylinder and fail without the tell tale fluid loss.

New master cylinder going in the next couple days. Will update on the results!

[tonythetarga]

it is possible for the fluid to leak past the O ring but it stays within the m/c but just won't hold pressure. If you have fluid in the trunk space you need to search for a source before you take the old m/c out. Could be a booster issue and you have fluid in there, could be a leak in the lines from the m/c. If your pedal went to the floor it is likely you now have air infiltration from wherever the fluid is leaking out of. I'd suggest putting the system under pressure with a motive bleeder and watch for leaks.

[sailchef]

I stood on my breaks in line at Taco Bell trying to get change out of my pocket when the pedal went to the floor.

Turned out to be a ruptured (rusty) line just below the MC where the lines all tie together.

[john walker's workshop]

maybe one or more calipers are frozen, resulting in dragging brakes. the heat can vaporize the fluid behind the caliper piston, and as you know, gas compresses and liquids don't.

[JBurer]

Picked up the car from the shop yesterday. New master cylinder fixed the issue.

Shop that did the repair supports 30 or so DE cars and several race cars. Owner tells me they've had customer cars have this failure out on the track - and recommend replacing the master cylinder every 3 years even if there haven't been any symptoms. That's for a track car.

Planning to disect the old master over the next couple days. If I find anything noteworthy, I'll share.