I've got a problem with my front brakes locking on, the car is a 98 Escort Gti Estate

When the car is cold they are fine, they start to stick on once it's been driven a few miles, getting gradually worse the more you're using the brakes, once everything cools down again, they release again

New calipers have been fitted, slight improvement but it hasn't solved it

What else could be causing it?

I'm guessing the master cylinder is a likely cause and I've read you can get a service kit for these, new seals etc


Incidentally, the engine has recently been changed and it's only since then I've started noticing the problem