Not sure if this has been covered before but new to this forum. Have just done a rebuild on a 3door Cosworth for my boss and having an issue with the brake system, all seems fine with pump,wheel speed sensors etc but when you press the pedal the ABS seems to be kicking back up the pedal and it is refilling the master cylinder with fluid as if something is blocked and not letting the pressure out. Car past the brake test in MoT but failed as when this problem occurs the abs light and red brake warning light come on, they go out again when pump has built up pressure again.

Thanks in advance for any help