Topic: 74 CB750 - Stuck Disk Brake Piston?

[Jim Harris]

Good morning!
Well, I changed the brake pads on my barn find 74 CB750 last week, but after putting everything back together and filling the lines with hydraulic fluid something didn't seem right. I decided to take everything apart last night and found the problem. I was looking for a piston to be in caliper A that would move back and forth by hydraulic pressure but I couldn't find one. I checked the service manual and figure 14-5 (see photo 32) shows a removable piston but all I had was a steel well that I thought must be the hydraulic reservoir but I couldn't see any holes or ports where the fluid would enter and exit and then I realized that the cap fit, so that "well" might be the piston itself fused stuck in caliper A (see photo 34).  Is that the piston? If so, how do I get it free or even if I do wrench it out will the side walls of the housing be so damaged that the new piston wont seal correctly?
Thanks!

[SOHC Digger]

The easiest way to get stuck pistons out is by adapting a grease gun to fit into the banjo-bolt hole and pumping the caliper with grease.  Even the most stubborn piston will easily walk out this way.

[70CB750]

The easiest way to get stuck pistons out is by adapting a grease gun to fit into the banjo-bolt hole and pumping the caliper with grease.  Even the most stubborn piston will easily walk out this way.

+1

[ekpent]

Usually the piston will pump out just using the hydraulic pressure from the brake handle as long as you keep adding some break fluid to the reservoir. Did you try that at all ? If you were able to get the old pad and piston cap off I doubt there is a whole lot of corrosion in there locking it in.
  You could try hooking it back up, bleed it, and pump it out.

[bjbuchanan]

You don't even really need to screw in the grease gun more than a thread, it pumps it out real easy. My bike sat for 20 years and it pumped out faster than it took to unbolt the thing

[70CB750]

I was always able to hold the gun on the bleeder and pump.

For the record, I did took one apart heating it up in the oven and wrestling the piston out - it was major effort.