Brakes lock up on 1990!

I have a 1990 Continental which is having a strange problem with the brakes. They work fine for a few days, and then actually lock up so badly the car is immobilised, sometimes in a dangerous place, and the car can't be moved.

This subsides after the car is towed and sits overnight. So far it has a new master cylinder and idle air valve.

If this can't be fixed it's too dangerous to drive, and I'll have to dispose of the car. Any assistance would be greatly appreciated. The shop I've been using doesn't seem to have a clue.

Thanks!

Welcome to the boards. First you need to recreate the condition in a safe location such as an empty parking lot on a sunday. Second determine if they lock up on their own or after you apply the brakes. Third determine which wheels lock. Only 1, 2, or all 4?

If only one locks after they are applied I would suspect a bad flex line (hose at the caliper). This can be checked by opening the connection from the master cylinder to the hose. The wheel should still not spin. Next open the connection between the hose and caliper or the bleeder valve for that caliper. If the pressure releases and wheel spins the hose is bad.

There are additional ways to check if 2 wheels lock and if 4 wheels lock. Post if you need them.

Good luck.