Brake pedal while stopped

[JustA5.0]

First time posting

I just replaced the brake shoes on my 87GT. Everything is great brake wise (pedal at the top), except when stopped for more than a few seconds (i.e. at a red light). The pedal slowly goes towards the floor, as if there was no brakes at all. Any ideas what may be causing this?

 

[bloopbloob]

did you bleed your lines? maybe a bleeder screw is loose? air in the lines?how's your fluid level? i'd start with the simple stuff like that first....

 

[JustA5.0]

I know what you mean ^^ checking the simple stuff first.

Nope, we bled the lines (there was air in the front passenger side actually). Fluid is topped up, parts wise everything was checked on the front and back for functionality. The brakes feel like a new car, until I am stopped for say 5+ seconds (basically just @ lights) than it's slowly towards the floor with the pedal.

MC on it's way out perhaps?

 

[dtlionsfan]

2 things,fluid leak or master cylinder.

 

[JustA5.0]

Alrite, checked the fluid today, still topped up, none of the lines are wet, or wetness around the discs/drums/ground. Must be the MC not able to keep pressure after a few seconds.
Thanks for the MC confirmation