Brake problem - intermittent

1997 Volvo 850 GLT sedan. 135K miles, excellent conditon. Had the front brakes replaced 5 months ago. Three months later comng to a stop the pedal went to the floor and no brakes. Managed to stop with the hand brake. Checked fluid and it was at proper level and monitored the floor for leaks - none. Drove for the next two months and not a single problem. Last night pulling into the garage the pedal again went to the floor and I hit my tool bench! Is it possible to have air in the lines and have this kind of problem so infrequently? No leaks and fluid is still at the proper level. Help - this is my teenage daughters car and I am afraid to let her drive it now. Can it be a problem with another system componenet?



Thanks!

The master cylinder is worn out.
Have it replaced before you or your daughter cause a serious accident.

Intermittent problems with the brakes like this leads me to believe the brake fluid is overheating somehow. If there has not been any exhaust work done that may have lead to the exhaust running too close to a brake line heating it up, I’d consider a brake fluid exchange or flush.

Brake fluid naturally absorbs water from the air, and collects contaminants from the brake system as it wears. This leads to a lowering of the boiling point where hot brakes may make the brake fluid boil. If this happens, no brakes, since the fluid has vapor in it. Let it cool, and they work again.

Thanks! We will get this done this week, change brake fluid as well.

Appreciate the help.