Yamaha twin piston brake caliper disassembly

I'm rebuilding the front brake calipers for my '75 XS650 project. They are the early Yamaha two piece twin piston calipers used on the '76 and older TX and XS 34mm forks, and also on some RD models. Removing the pistons can be a little tricky. Mine weren't seized, but sticky enough that compressed air wouldn't do it. Here is the method I used to get the pistons out. First separate the caliper halves by removing the four fasteners, leaving the bleeder screw in place.


The fluid crossover ports are in the center of the two smaller bolts.


Flip one around and bolt them together like this.


Then hook up a master cylinder.


Get two C-clamps (which don't need to be as big as the ones I used) and pump up the master cylinder. The clamps keep the pistons from popping out as pressure builds. Let one come out far enough that fluid leaks out from around the piston, and then push it back in just enough so it seals again. Then pump the other piston completely out. Remove the clamps, and the first piston should be free enough to just wiggle it out by hand, or use a rag (to protect the piston) and channel lock pliers if necessary.


Both calipers apart and ready for rebuilding.