This post is for information only, I hope it proves useful if it happens to you.
The disk brake callipers used on this Focus (and many other cars) are sliding action single-sided hydraulic and their operation relies on the ability of the calliper to slide across to bring the static pad into contact with the brake disk, when the piston moves its own pad against the disk. After removing the braking force, the design then relies on the motion of the brake disk to push the calliper away slightly and free the disk from the fixed pad and the moving pad.
Yesterday evening I noticed that the acceleration seemed down and a little later I noticed that the car slowed more rapidly than usual on the over-run. When I stopped and looked at the front brakes, they were hot, hot, hot!!
A combination of road dirt, brake dust and a little rust had stopped the sliding action, so when the brakes were applied, they were left dragging more than expected. You could temporarily ease this by using a wooden mallet to knock the calliper to and fro a few times, but it really needs cleaning off and the sliding surfaces treating with a high temp grease ( I use CopperEase) The car is garage-serviced every year in November and both the pads and disks are in good condition, so for both front brakes to have the same problem in such a short time may be due to the amount of rain and mud in our country lanes around here.
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After removing the braking force the design then relies on the motion of the brake disk to push the calliper away slightly and free the disk from the fixed pad and the moving pad.
Sorry to be a pedant, but this is not strictly the case. The return mechanism is built into the caliper seal, which sits in the cylinder bore at an angle, and thus only the tip of the seal is in contact with the piston.
When the brakes are applied, the piston moves forward slightly, thus causing the seal to flex forward in its seat. When the brakes are released, the seal pulls the piston back into the bore.
Before the perfection of the caliper piston seal (albeit some years ag), a lot of effort was put into the return mechanism, which included the use of springs and other devices to ensure the piston returned into the bore, but not too far.
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"The car is garage-serviced every year in November and both the pads and disks are in good condition, so for both front brakes to have the same problem in such a short time may be due to the amount of rain and mud in our country lanes around here. "
Or it could be that the service schedule only calls for a brake inspection without removing the wheels and so no sliding action is checked and no grease is applied. Inevitably, brake problems will occur if pads are not worn down enough for replacement. Sometimes replacing the pads at service time might actually help prolong the life of the calipers, even if the pads are not techinally due for another few thousand miles.
Thats not necessarily the case if it was not a main dealer service.
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Might be worth checking the piston action. Can they be pushed back easily and moved out again on the pedal? Are the external piston seals intact? Also worth checking the brake hoses have not collapsed. Although it is OK to use a copper grease on the back of the pads, you should not use it any where else. It just attracts dirt and dust and can make things stick. Maybe take the pads out and wire brish all the surfaces that slide.
I had this problem using a known quality (M) pad on a Honda. Finally given the small saving went back to a Honda pad, and the whole thing from pedal feel to stopping felt so much better.
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