Avid Jucy 3 Piston Removal (seized)

Question

I have a set of Avid Juicy 3 calipers that I have sucessfully replaced the pistons and seals on. Getting the pistons out of one of the calipers was not so easy though, and I ended up drilling the middle of the piston, putting in a self tapping screw and pulling out the piston with a mole wrench, like the cork from a bottle. This was OK because I was renewing the pressure foot as well as the seals. The downside was the little dimple left in the caliper body where the drill overshot or the screw pressed.

I have a couple of other caliper bodies in need of some work with a similar problem and wonder whether there is a better method or a trick to ease the piston/pressure foot out (potentially so it can be reused!).

I have tried compressed air with no success and hydraulically seperating the caliper halves with rubber over the port then pumping the bleed port with dot fluid and the syringe, also no go. I feel like I'm missing something but it may be that the caliper is completely siezed and the corkscrew is all that's left.

Answer 1

Not sure if it's helpful but here is a generic plan for popping pistons with a compressor.

Use this kind of blower attachment, with a conical rubber or plastic nozzle.

Split the caliper in its two halves and drain the fluid best as possible.

Most caliper halves will have one side with the hose inlet, and then when you open it there will be a port for fluid to pass through into the other half. The other half will have the bleed valve, which you keep closed, and a port for fluid that joins with the one on the other half.

Starting with the half with the bleed port, put it down on a bench and take a rag and hold it over the piston so it doesn't go flying when you pop it out. Then jam the conical air blower into the fluid port and let it rip. Typically they come out with a loud pop; it's an actual explosion you're creating so be ready. The other side is the same except you have to have one fingertip covering either the hose port or the fluid port on the caliper split while the blower jams into the other entry point.

If this doesn't work then the piston seal is probably some especially terrible kind of destroyed, like expanded from fluid contamination. I don't have a great generic plan for what to do then, as it's a rarity for me that I'd be trying to bring a system like that back to life.

Answer 2

I actually finally just managed to solve this puzzle on my old juicy 7 brakes which I'm renovating. There is a simple trick which I employed to get better access to the pistons and force them out hydraulicly. Separate the caliper halves and then re-attach them, but only with the banjo bolt and bleed screw, and with halves rotated against each other by 180 degrees. You still get a hydraulic seal but have much better access as each piston is now facing the open air where you can get a clamp on them. Next open the master cylinder cover on the lever and clamp it upright in a vice, then bleed the brake by feeding fluid into the master cylinder and drawing it through the brake with a syringe on the bleed nipple, as you normally would while bleeding. Then you can pump the lever to force more fluid into the caliper and force the pistons out. Continue to feed more fluid into the master cylinder as the pistons get further out. If one of the pistons is coming out faster then you now have plenty of room to clamp it. Wait until the dominant piston is nearly all the way out, clamp it, and then continue to pump the lever and feed more fluid in until the other piston is nearly out. Then remove the clamp and continue to pump until both pistons pop out. Cheers.