I’ve rebuilt a few Juicy 7 calipers. I ride through the winter so my calipers pistons stick about every 18 months and need to be rebuilt. What I’ve found is road dirt gets onto the sides of the square O ring that provides the seal between the caliper piston and caliper body. That O ring then expands and prevents the fluid movement of the caliper piston. So, essentially, what you need to do is take all the parts apart to clean the square O rings and the square O ring groove that seats the O ring in the caliper.
To get the pistons out and be able to reuse them I do the following. First, keep the caliper secured on the mount and to the hydraulic system. Second, take off the bicycle wheel, brake pads, and brake pad springs and small metal caliper hole cover.
The goal is to use the hydraulic pressure to remove each piston and it is a time consuming process but it works. Get 2 C clamps and two pieces of thin 1/8″ thick and 1/4″ wide metal rods about 8″ long that will fit between the caliper holes. Home Depot sells these rods. I’ve used a pair of 5mm box wrenchs the first time. Form a jig clamp that will hold one of the two pistons in the caliper body using the 2 C clamps and 2 metal rods. Squeeze the brake lever slowly until the non clamped piston completely comes out of the caliper. Brake oil will fall to the ground so make sure you have a small bucket under the caliper.
Take the caliper apart, clean the square O ring,and the groove that the O ring sits in – I use a L shaped ice pick. Reassemmble the now clean half of the caliper, attach to the bike, and bleed. Now, secure the other caliper piston using the 2 C clamps and 2 metal rods. Repeat the process.
I know this is a major pain and long process, but you should be able to reuse all of the parts including the square O rings and pistons thereby saving you $40/caliper in replacement parts.
I tried the air pressure method, but even 180lbs of pressure wouldn’t release my siezed pistons from the caliper.
