Rep Power: 0

I have had 2 incidents in the last 6 months, where, after driving for a while (45-60 minutes) in stop-and-go traffic -- with lots of braking on and off --, that the brake pedal fails to stop the car after getting off the highway.
I suspect that maybe the brake master cylinder is faulty? Perhaps temperature of the brake parts is contributing to this issue?

This morning I had been in stop-and-go traffic for 60 minutes, with heavy brake use. I left the highway, and after more heavy traffic with lots of braking, I turned the corner. After driving for a few blocks, I found that when I pressed the brakes, the pedal went to the floor, and there was no stopping. I had to use the emergency brake to slow the car down. One thing that I did notice earlier while on the highway, was some metallic clinking coming from the front wheel areas. After waiting a few minutes, the brakes started working again, and the clinking sound went away.r leavi

This incident reminded of a similar incident that I had last May, also upon exiting a highway. I was on the highway for 45 minutes of stop-and-go braking/driving, then exited the highway, and stopped by the side of the road to check directions. When I started the car up, and put the car in drive, the car moved forward but I was unable to stop it when I pushed on the brakes. The brake pedal went to the floor. I used the emergency brake to stop the car. After I turned off the engine and waited a few minutes, the brakes began to work again.

I wonder if the brake master cylinder is faulty? or maybe the brake pressuring system? In both of the above cases, the brakes failed after much stop-and-go driviing and after having stopped for a few minutes. I also wonder if the clinking sound I heard this morning may be related to a failing brake system. Also, maybe there is a problem with heat

 
Rep Power: 518

Kinda sounds like a brake is dragging, and after a while it's so hot the fluid boils, and at that point braking action is lost/pedal goes to the floor.

After a drive get out and feel the wheels. Is one or more scorching hot? Smoke rolling out and stinks like hell?

Can you roll the car by hand (shifter in neutral)

 
Rep Power: 366

Can't see what you are doing driving, so driving style also could matter. Don't follow too close... (it's more likely dragging brakes, like ezone is saying, though, but hey, thousands of people reads the threads in here, so need to say )