Topic: pop out the piston on that frozen rear master cylinder, easily.

[dboblet]

OK, so the front brakes on my project bike are workig great, but no rear master cylinder.  So, I bought one on e-bay (cheap) and frozen solidly.  I removed the ring clip and pulled out the acturator rod, but the piston wouln't budge.  So, I attached it to the front brakes instead of the caliper, squeezed the brake handle a few times (hard) and the piston slowly squeezed it's way out.  I lost a bit of brake fluid and had to bleed the front brakes, but now I have the rear master cylinder apart with zero damage ready for a rebuild.

[bradweingartner]

Check. Great tip!

Hydraulic pressure for the win.

[Polak91]

Awesome advice!

Rear caliper piston was completely lodged in the caliper. Bolted it back up to the bike, without the pads so the caliper could move, bled the brakes. Then pressure built up in the caliper piston seat and the piston moved out slowly. Had to push the last half inch out with compressed air but the hydraulic pressure pushed more than half of it out.

[worst650ever]

I have had a lot of luck with plugging the hydraulic line hole with a bolt, loosening the bleed screw, and attaching a grease gun to the bleed screw - it's a nearly perfect fit!

An air powered grease gun makes this even easier, but a manual one works just as well.  You will have to clean a bunch of heavy grease out of the caliper afterwards, however