Master cylinder:
1. Hole to fill the fluid.
2. Hole to bleed the master.
3. Hole to feed thru the lines.
4. Hole for the piston to push past [holes 5-6] and return home.
5. Hole to add fluid to the lines when pads wear = The tiny hole.
6. Hole to return fluid and zero out the pressure back to 14.7 psi = A little larger hole.
Caliper housing:
a. Housing holds a square made ring.
b. Housing holds a piston.
c. Housing has a square groove for the square or quad-ring as opposed to an o-ring.
d. Housing has a hole to feed fluid behind piston and pushes piston in one direction only. Why? You have no pump once you release the lever. The fluid returns to zero pressure.
Reversengineering:
When I press MC piston in one direction, I have to cover the tiny hole so I am now sealed. When open, it has to feed fluid or keep the fluid there ready for a stroke. So it feeds from the reservoir. The little larger hole pushes fluid back into the reservoir it came from. When the stroke happens, there would be vacuum behind the piston if there wasn't that little smaller hole pulling a neutral pull of fluid to equalize 14.7 being drawn from behind.
When I release pressure, the fluid built up behind the piston has to be pushed back out, so this sends fluid back out the little larger hole. Notice how I made no reverse vacuum but to have that fluid return to 14.7. I first had to push the liquid and that is more instant than thinking there is an air cushion between lever and liquid. So have we established we have zero fluid pulling back on the piston but moving back to zero only? No fluid could help pulling piston back.
Quad-Ring:
Rubber has memory. This ring sits square in this machined groove's OD. The piston sit inside the ring's ID. The piston has enough slide so as not to cock to the side, some squid sands the machined finish down. That does not stick the piston. Take your finger and stick it thru you making a round hole with your other index and thumb. Your round hole is the quad-ring. Your finger is the piston. Push your finger until it moves some, then stop. Now, move your finger in and out without moving your finger from your circled fingers.
Feel that give? That would be like how the quad-ring moves the piston back to square. That's where memory is moving the piston, because there is not wear you can see if we stopped the bike a few times. It takes thousands of miles to move the pistons out. It takes every time the piston is pushed, so does the quad move back to square. So this movement is more what pulls back the pucks or more there is zero puck pressure. There is no puck pulling back. There is just puck pressure released and with the memory pulling back the piston, your slight warp that comes around and pushes this one side inward is more disc release [if] not fighting that memory coming back into the disc again.
Disc Drag:
Thru time/neglect, contaminated fluid builds up under the quad-ring. This buildup under the quad will set piston from moving the piston back. So the piston is more set at this position. No rebleeding may help. What might clean around the quad will not clean out what is under the quad. Thus the rebuild, the new quad seals, the cleaning of the groove of all contaminants. No marring of finishes when rebuilding.
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