I have a 2001 Ford Focus, 96000 mi. With brake issues.
I took it to a repair shop to have the master cylinder and boost replaced. The shop said the first cylinder we gave them (new) was faulty, so we got them another new one. They said THAT one was faulty, so we got them yet another one, along with a new boost, since they said they got fluid in the one we gave them. 3 cylinders, 2 boosts and a month an a half later, I get my car back and I go to drive it to work the next day, and I get about 5 miles from my house and there is smoke pouring out of my car and my front brakes locked up. I took (towed) it to a different mechanic who has had it for a week now. They have looked at it, consulted with a few other mechanics, flushed the entire system, and they have no idea what is wrong with it.
It runs fine when the engine is cold, but after the engine gets to normal temperature, the front brakes lock up and it starts to smoke. It does this even when the car is only started and sits for about 20 minutes. HELP!
Pretty crazy sounding.I would normally say it sounds like a booster valve, but I think you may have eliminated that. If they made sure the rod is aligned good, and cant be dragging on the boot or bulkhead. If that is ok, lets start thinking crazy thoughts. If it only happens when the engine warms up, and it happens to both front tires, I would jack the rear tires and see if they are getting brake pressure also. There are PCRV's in the rear brake line to help prevent locking up of the brakes, so maybe all of the brakes are getting pressure, but just the fronts are locking.
If all brakes are getting pressure, and it only does it when the engine is warm, Im leaning toward master cylinder. I know its been changed, but it is in the engine compartment and it will feel some heat off of the engine.
If it is just the two front brakes, look to see where the fluid lines are routed? Do they run near the engine exhaust? Maybe some heat shielding was removed and allowing the fluid to create a vapor lock and hold pressure on the brakes. Ok. That is really reaching.
Ive been trying to convince myself that it could be the HECU of the anti-pock system, but I have never heard of one of those making the wheels lock up.
Good luck and I look forward to seeing what fixes your problem.