Break vacum problem

[Custom/Ten]

I will leave you will one more wild theory. First there are some things that can cause your master cylinder pistons to move forward. The thing is though that your brake pedal is not(should not be anyway) attached to your master cylinder in any way. It's not an attaching rod, it's a pushrod. What I'm saying is if you had your master cylinder pistons moving forward on they own, that should not drag the pedal down. I say remove the master and see if the pushrod is stuck in it, jammed together. While your at it take snipers advice and see if you have a power brake mc, then see if you have an adjustable booster rod. Like I said before he though, I really don't know what's going on here, good luck bud!