I had a heap of trouble with my BS6 rear caliper (on EVXX), in the end I ordered new pistons, seals and also new seals for the master cylinder, when the parts arrived I noticed that the new piston and seals were different to the original OEM. The old seals were very slightly tapered as opposed to the new ones which were square. With the old tapered seals this then enabled the pistons to very slightly tilt/skew on an angle and hence the reason they jammed when trying to retract. Also the old pistons were flat on the rear face, where as the new ones had a shoulder and were also a couple mm larger in depth overall. I don�t think the pistons made a difference, but the piston seals definitely did. Since rebuilding and replacing the brake fluid (Dot 5) the brakes have been perfect. On bleeding the system, I bled it the same way as bleeding a normal car; 1. Ensure fluid in the master cylinder reservoir, 2. Pump pedal, 3. Open bleed on caliper � use a small bit of clear hose on the nipple pointing in an upward direction and then down into a catch container this way no air can go back into the system, 4. Close bleed on caliper, 5. Release pedal; continue until all air is expelled, ensuring fluid is always in the reservoir. This is much easier with 2 people. Also if your system is all clean, catch and re-use the fluid expelled from the caliper, but only if your system is clean. I can guarantee if you follow these steps your brakes will work perfectly. No need to go out and spend a fortune on new brakes!!!
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