so currently having a problem with my brakes. when the car is off and I press the brake pedal, it pumps, will turn hard. when the car is on it loses all of its pressure and start to sink down. know I know that it could be one of three problems areas: abs, master brake, or the brake booster. I have checked all my brake lines and no leaks, my brake, and no leaks. I did bleed the brakes for air and some did come out but not much. I did bleed from the master brake, each break, and from the abs mod. it's still doing something. I want to check the abs to see if that's causing the problem before I check the master brake and the brake booster. does the abs on the 13 v6 mustangs have a check valve-like what other fords have.

 

I do not think there's an ABS check valve. It's a manifold with entry and exit points and electronic valves to cause the ABS to work. That you got air out at the calipers means there's likely air in the ABS module, which is a bad thing(tm). You can't get it out easily. You'll have to do the procedure which requires a computer/scan tool to do to get the ABS module bled properly, or you'll have to go about 50 MPH and then STOMP on the brakes... I've heard that latter will figure it out. Might have to do it twice or more. Not sure on the MPH, but something kinda stupid like that. This is why it's important to not let air into the system at all.

Hope that helps. And if I'm wrong on any of this, I do hope someone jumps in and slaps me proper for to learn us both.

Good luck!