I replaced all components of the front and rear brakes. The brakes are fine until you drive a little ways. Then the front brakes start grabbing and eventual they lock up so hard the pads smoke and then the vehicle doesn’t move. After cooling down the caliper pistons release. The only things that haven’t been replaced are the metal brake lines and the brake booster. New wheel bearings, rotors, pads, brake lines to the calipers which I replaced twice in case of manufacturing defects, and the master cylinder. New fluid throughout the system to flush the old out and the system bled of any air. What’s left? Thanks
What makes this problem better or worse?
Driving after the system has cooled down
How long has your 1990 Ford Aerostar had this problem?
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If you can indeed verify that all hoses are clear -- run fluid through each into a jar to verify that fluid is coming through -- and the calipers are not at all sticking (which would be quite a coincidence to have both front brakes locking simultaneously), and you can verify that the master cylinder is working as designed and has been bled properly, then the only other component I can think of is the proportioning valve. This vehicle has no other components. Ensure the correct brake pads and rotors and calipers have been installed, of course, also, for the application.
