We have had a lot of discussions of dragging brakes and many seem to have trouble finding the return or relief port that permits fluid to flow back into the Master Cylinder (MC) reservoir when brakes are released. This applies to front and rear, any year model, and even the Chinabay MCs. I am including a photo however of a 1979 GL1000 front MC WITH RESERVOIR REMOVED. On most, it is important that the plastic reservoir is removed as it blocks view of the port. And that is a good thing, as it also prevents a geyser of brake fluid from squirting up every time the brakes are released!
BTW, this not only permits fluid pressure to fully release the brakes, but it permits fluid expansion due to heat. Brakes seizing up as you ride? This could be your culprit!
I have enhanced the photo by changing the contrast and brightness of just the lower port in the photo, which is the return port. The upper port in the photo is the supply port. You may have to zoom in, but the tiny black hole should be evident (I didn't draw it, just enhanced the contrast so it could be seen). Now that you have seen one, you can look for yours when you rebuild your MC. On rear MCs, it is sometimes behind a port on the side that has a 14mm hex head and standard aluminum brake hose gasket covering it. On one of my Chinabay rear MCs, it was behind the nylon adapter to the remote reservoir hose. This hole MUST be open to allow free fluid flow, but must not be enlarged beyond original size or you will loose some braking (it is open for the very first part of each stroke, but is small enough that the much larger piston flow overcomes it, and it is quickly passed by the piston's first cup). A small unwound guitar string is ideal for cleaning it, even if seriously plugged.
BTW, this not only permits fluid pressure to fully release the brakes, but it permits fluid expansion due to heat. Brakes seizing up as you ride? This could be your culprit!
I have enhanced the photo by changing the contrast and brightness of just the lower port in the photo, which is the return port. The upper port in the photo is the supply port. You may have to zoom in, but the tiny black hole should be evident (I didn't draw it, just enhanced the contrast so it could be seen). Now that you have seen one, you can look for yours when you rebuild your MC. On rear MCs, it is sometimes behind a port on the side that has a 14mm hex head and standard aluminum brake hose gasket covering it. On one of my Chinabay rear MCs, it was behind the nylon adapter to the remote reservoir hose. This hole MUST be open to allow free fluid flow, but must not be enlarged beyond original size or you will loose some braking (it is open for the very first part of each stroke, but is small enough that the much larger piston flow overcomes it, and it is quickly passed by the piston's first cup). A small unwound guitar string is ideal for cleaning it, even if seriously plugged.
