Land Rover Repair: land rover disco brakes, caliper piston, piston movement

Question
QUESTION: I have a 1997 discovery le, I have replaced the front calipers, pads, and the master cylinder. But now my front brakes are sticking on. What could be causing this?

ANSWER: Hi Chris,

I would remove the caliper, insert a block of hardwood or a brake spreader/clamp and then have someone apply the brake (lightly) to witness the pistons movement.  Do the pistons come out smoothly from the bore?  When the brake pedal is released, is it easier to retract the pistons or is the pressure constant? Spray some brake cleaner around the pistons to ensure there is nothing there to cause friction.  Make sure the seal is seated properly. Are the pads installed correctly? When the brake pedal is released, is there any movement of the brake pads - any at all?  Did you bleed the lines of any air?  Have the brake fluid replaced by a garage - they will have the best equipment to flush and replace the brake fluid and ensure no air is trapped within the system.

Best of luck,
JohnMc

---------- FOLLOW-UP ----------

QUESTION: I have bled the brakes and I'm not getting any air bubbles out the lines, the piston movement looks good to me. The brakes work good for a little while then the calipers stay pressurized and if I loosen the bleeder screw the pressure bleeds of and the brakes are ok for a few more minutes the stay pressurized again. This will only happen while driving.

Answer
Hi Chris,

how does the brake pedal feel?  Is the pedal soft or stiff?  Does it press down slowly or does it remain hard and little or no movement?  If you are sure your pistons are moving in and out with ease, there is no corrosion present on or around the pistons, then it could be your master cylinder or maybe the SLABS ECU or ABS modulator.  No brake related codes present?

Generally, seized brakes can be due to caliper piston or rubber seal failure, master C, SLABS ECU, or even the ABS system.  Water can get in behind the piston and start the corrosion process.  You can buy kits that allow you to rebuild the caliper - make sure you clean all the rust out. Did you use any brake lubricant?  Are the piston seals in good shape?  You could pop out the piston and see if there is any corrosion behind it. As for ABS system (including HDC, TC) this is a problem area I suggest you have a pro deal with.

Best of luck,
JohnMc