Brake Failure

[Bricktop]

Hi All,

Just had a top weekend at DATC with earlybay, unfortunately had a bit of a brown trousers experience 20 miles out when the brakes failed, pedal went all the way to the floor with no effect! after rapidly pumping the pedal i got a small amount of braking but once i'd released the pedal it needed pumping again until even that had no effect? No fluid loss as well!
I was all prepared to get the dreaded RAC lift home after the weekend when bizarrely the brakes now work as normal?? obviously now i have no confidence in them so i'm thinking of replacing the master cylinder, question is I thought they were a twin circuit system so this couldnt happen unless both circuits in the cylinder simultaneously failed? sounds a bit unlikely but would appreciate any thoughts in this before i waste a hundred quid!

Cheers

 

[Moseley]

Symptoms of master cylinder failure are as you describe - I.e. Rapidly pumping the pedal should get you some braking action again, but if you push it and hold it, the pedal will sink to the floor. It may well be that it has been failing for some time, but unless you'd done any hard, prolonged braking, you may not have noticed the sinking pedal syndrome. The fact that you haven't lost any fluid does point to this though.

The only thing I could think of with the dual circuit not working is the possibility of air being in the second circuit? It wouldn't take much so that the pedal hit the floor when the other circuit failed.

 

[davechorlton]

Could be you have a brake binding and te heat is boiling the fluid which then renders it useless...Ask me how I know!

I had a failure like this and when the fluid cools it works... It turned out to be a front caliper seized on my crossover.

 

[Tofufi]

I was wondering too if you had overheated your brakes.

I did that in my bus coming down the Pyrenees - 7 miles of steep downhill (covering more than 1km vertically down). Despite using the brakes as little as possible, about a mile further on the flat, I had no brakes as I'd boiled the fluid. I was very glad I wasn't still going downhill at that point :lol:

I let it cool, and all was well again for the rest of the trip (though I did change the fluid when I got home).

My bus has discs on the front, in my experience drums get hot much quicker and cool more slowly.

If it happens again, the handbrake should still work to slow you, though not especially effectively...