Mazda 5 breaks went a bit odd today... Please help!

I left my car running today as it did not start earlier and had to jump start it. There was no hills anywhere and I had a plumbing job to finish! Stress.. Car was running in the driveway for about half an hour.....

Then on my way home the breaks were odd and did not work very well on the 2nd or third push down.. nearly went into the back of someone at traffic lights!

I tested it on the way home and yes - first pump on the break stopped the car fine if I let go and pressed the break down again hardly anything. It was rock hard to push down, didn't become soft....

Later today I tested it and now it is fine!?!?!?!?

Was it the heat from the engine? I checked the heat gauge occasionally and it kept at half way...

Very very odd.. This senareo my well happen on the motorway if I'm in a traffic jam... Could be fatal..!?!?!?

Did u check the brake fluid?? Keep an eye on the reservoir. I'd speculate a failing master cylinder or there's a (starting) leak in the system. The leak you can observe by loosing fluid when pumping the brakes. With the car on, have someone pump the breaks a good 6-8 hard times to see if the reservoir gets low. I had a leak develop on an older car at one of the grommets. There have been other Mz5 posters in the past having similar brake issues caused by a faulty MC!. I can relate in the unexpected feel of having the car plow forward with the brakes fully depressed - scare as hell... Good luck.

More than likely your master cylinder. Same happened to me (freaky) and I had the master cylinder replaced good as new. Good luck...

I also vote master cylinder. When its not being used (1st pump) the pressure is able to build over time, but after that 1st pump, it can't maintain pressure, so you feel the brakes sponge out.