caliper -- internal plumbing

I installed my caliper with new seals and ss pistons but could not get any brake fluid out of the bleeder valve. Took it back apart and had a look. In the outside piston side there are two ports. The one right under where the hose comes in I assume feeds the fluid into this side which it does fine. If try to squirt parts cleaner through the inlet or blow compressed air while holding my finger over this port I can't get anything through. There is also a second port just below the first and I also can't squirt any parts cleaner or get any compressed air through it either. It appeared that very little brake fluid made its way behind the inside piston. Spraying parts cleaner in the bleeder valve opening resulted in a spray from a port on the inside piston area. I know I have a clog somewhere so that brake fluid is not getting to the inside piston side and out the bleeder. Any suggestions on how to proceed?

Hmm, a new one on me. What could clog but corrosion and or rubber hose or puck seal rubber? Not much dissolves rubber, certainly not brake fluid much or acetone plus not likely rubber anyway. I'd suspect corrosion Al and iron puck rust sediments, so might try a boil in vinegar to both expand the ports and dissolve corrosion collection that then might blow out. Alkaline detergent like dishwasher stuff can eat up Al, especailly heated but eats the looser crusts first if vinegar boil don't do it but got to watch time and check port opening hints or can eat up the puck seal clearances. Pretty neat paper weight through if can' get cleared eh.

They had to make the passageways somehow. Maybe if you can figure out how they manufactured it then you can attempt to simulate that.

Oh Brother what other cycle besides Spragtrophe would one be advised to back engineer the production process just to clear a short simple fluid passage? Seems like I probed mine with a thin wire but didn't seem to go but 1/2" and wouldn't turn the corner. I could not fathom how they created the hidden deep back passage even seeing the openings. One thing I'd also try on esculating attack would be heat the caliper to like 500'F then maybe knock it about on hard wood block, using line man's - welder gloves or old base ball mit or thick rags. If its organic should char to brittle ness and if ferric would expand with the Al so shockable dislogdible and if Al might also fall out or crumble to pressure spray. I see no way to apply hydraulic fluid force Yes I've dreamed of a small dia spring snake to chase these worm holes.

Mentioned in other threads (but not tried by me personally) is the grease gun method of loosening up the pistons for horribly stuck calipers.

If I understand the issue, you can apply air pressure to the hose inlet and nothing comes out. Might give the grease gun method a try as it exerts a lot more pressure than air, and just might dislodge whatever is constricting the passage. Difficulty here is getting a match between the outlet side of the grease gun and the caliper inlet - might have to make up a hose or whatever to get a tight connection.

Drills do not go around corners. Every passage is straight... IIRC when I rebuilt mine, the passages had holes drilled from two directions converging to make the "bend" (I can't help but try and visualize the production of a part, a machinist thing) so take the pistons out and wire out the passages, blow and solvent to finish.

concours said:

Drills do not go around corners. Every passage is straight... IIRC when I rebuilt mine, the passages had holes drilled from two directions converging to make the "bend" (I can't help but try and visualize the production of a part, a machinist thing) so take the pistons out and wire out the passages, blow and solvent to finish.

Click to expand...

+1

Old brake fluid can get all crusted up in the bleed gallery and forms a crystalline gunge which can be a bit of a pain to get out - I use a twist drill-bit, but not in an electric drill - just twirled between the fingers works for me.

An ultrasonic cleaner may get in there and break up whatever is gunked. Works wonders for carb jets and passages.

I have also used a bit of baking soda in the passage, then pour a little vinegar in there to get a bubbling reaction.

Thanks for pointing out the passages were straight drillings. I was able to clean it out using a 9/64th drill bit, gently tapping with a hammer and twisting by hand. Back on the bike and bled down nicely.