The first 5 posts give great advice. I would check those items first. Rear backing plates, return springs and the 3 flex hoses. If none of these things solve the problem, here are 3 much less likely but still possible things that can cause this situation. 1. Rear wheel cylinder pistons are sticking. If the wheel cylinders are rusted, when you apply the brakes cold, you are pushing harder than you might think, when you finally apply enough pressure to make the wheel cylinder pistons move and apply the rear brakes, the front brakes are over applied and may lock. 2. The front caliper pistons are sticking. This can be caused by crud and rust collecting inside the caliper pistons over years and the rubber square cut O-ring losing it's memory over many years. When you first apply the brakes, the piston is supposed to move past the seal and the seal is also supposed to twist in it's groove and act like a return spring to very slightly retract the piston when you release the pedal. Just a little, like .010"-.015" . If the groove is full of crap or the seal loses it elasticity, it won't return and locking is possible. 3. Finally, it's possible the combination valve is not working properly. This is very unlikely and I wouldn't condemn this part until everything else has been addressed. Let us know what you find out. Good luck with it.
If you find any of the things I mentioned to be the problem, here is how I would repair. Rear wheel cylinders: just replace them. Front calipers sticking: I rebuild them. Super easy to fix. 2 kits are 10.00. Takes 30 minutes to rebuild a pair. 3. Combination valve: replacement is the only practical repair.
|