CB550K update - front brake caliper rebuild

Today I managed to find time to tear apart and rebuild the front brake caliper on the 1977 CB550K that I'm presently restoring.

The piston and pad would move out and apply pressure to the brake disc, but wouldn't necessarily retract. I figured this was a result of either gummed up internals or air in the caliper itself, allowing pressure to be built up and retained.

The brake handle also felt rather squishy, and you could hear what was very clearly air bubbles in the master cylinder and brake line.

Using the brake handle to slowly push the caliper assembly apart, I was able to remove the brake pad and piston.

Brake caliper showing cylinder, gasket groove, and pad recess.

The internals didn't look too bad. I wiped out as much of the gunk that I could and pulled the old rubber gasket, then dipped the caliper and piston in Gunk carb dip for about 30 minutes.

Outer end of piston.

I then went back over the inside surfaces with a Dremel and steal wire brush to get the loose rust and surface pitting knocked down. After that, sanding with 600 grit wet/dry sandpaper and some WD-40 made the cylinder and piston surfaces nice and smooth. I also went over the inner pad walls to hopefully prevent the brake pad from hanging up.

Inside piston surface.

A quick test fit showed that the piston moved freely inside the caliper, and that the pad had plenty of clearance. Reassembling, I used some WD-40 to lubricate, and installed a brand new gasket. I compressed the entire assembly before reinstalling on the caliper swing arm to minimize the amount of air that would need to be bled from the system.

Back side of the brake pad showing nylon spacer.

I took a hint from various forums online and picked up a Speed Bleeder. They're about $7 and well worth the money. The old bleeder was getting rather nasty, so I wanted to replace this part anyway. For the record, the correct side for a 1977 Honda CB550K is 7.0x1.0mm, or part number SB7100.

Speed Bleeder. 

The Speed Bleeder is really a simple concept, but makes bleeding brakes a hundred times faster and more effective. It just has a spring loaded check valve internally that automatically closes the valve after you're done pumping the brakes. Attach a clear hose to the end so you can tell when the air bubbles have gone away and you're set. Bleeding the brakes on this bike took less than a minute, and I'm confident that I got 99% of the air out of the system. This combined with the stainless steel lines, rebuilt master cylinder, and rebuilt caliper resulted in very hard and sensitive brakes with no detectable "squish."

Fully assembled brake caliper.