The rubber hoses that go to the calipers can break down internally over time. As a result, you can force brake fluid through them to the caliper, but when you release the brakes, there isn't enough pressure to push the fluid back. Thus, they stick. What to do is this. Safely lift and secure the front tires. See if they turn. If they do, hit the brakes. The tire should stop. You should be able to spin it again when you release the brake pedal. If the tire won't spin, loosten the bleeder valve to see if that allows the caliper to release. If it releases, then the rubber hose is most likely the problem.
As far as the proportioning valve, it is designed to apply 40% pressure to the rear and 60% to the front. The front does most of the stopping. That is why they wear faster.
Let me know what you find or if you have other questions.
Sunday, November 21st, 2010 AT 5:26 AM