I have a 94 accord with 115,000 miles. I am not leaking any brake fluid but when i am stopped at a stoplight, my brake pedal will sometimes slowly sink all the way to the floor. This happens much more often when it is warm outside. I recently had a rear brake job done so it has been recently bled. Is this most likely an air in the lines problem or a master cylinder problem?

 

Most likely a bad master cylinder.

 

Yep, bad master cylinder. Exact same thing happened on mine back in July, and a new MC fixed it.

I would recommend getting a new MC from Honda. Those remans can be a pain in the *** if they're not done right. I made that mistake when I replaced mine, and I ended up with 4 locked wheels (not fun! ). Huge headache that was, especially since I was supposed to go out of town the next day, lol

 

Definitely a master cylinder. Sometimes when you flush the old fluid out, you flush the junk that was keeping it sealed too. I had the exact same problem after I flushed my brakes...