When you upgrade to st170 discs and calipers on just the front you will lose pedal or only get half if you get what I mean and the fact you got a disc set up at the rear will again make it worse due to the amount of fluid required to move the pistons. It is recommened that you use a mk1 mondeo master cylinder and servo combo to over come this problem. The mk4 escort m/c servo just simply isn't up to the job.