rear master cylinder is pissin me off

Common ordinary household rubbing alcohol makes a good cleaner for brake parts. And is a good final flush to remove residue of whatever other cleaning agents and soaks (i.e., PBBlaster, Kroil, Marvel Mystery Oil, 50-50 mixture of acetone and ATF, etc.) were used during the restoration process.

The alcohol may be blown off with compressed air, and the internal parts then coated with brake fluid before final reassembly.

Won't hurt to try soaking in Marvel Mystery Oil, but am thinking it won't penetrate nearly so well as would a 50-50 mix of acetone and ATF, or Kroil or PBBlaster.

Good Fortune!

Patton wrote:

Common ordinary household rubbing alcohol makes a good cleaner for brake parts. And is a good final flush to remove residue of whatever other cleaning agents and soaks (i.e., PBBlaster, Kroil, Marvel Mystery Oil, 50-50 mixture of acetone and ATF, etc.) were used during the restoration process.

The alcohol may be blown off with compressed air, and the internal parts then coated with brake fluid before final reassembly.

Won't hurt to try soaking in Marvel Mystery Oil, but am thinking it won't penetrate nearly so well as would a 50-50 mix of acetone and ATF, or Kroil or PBBlaster.

Good Fortune!

Good points from you guys, thanks for that, I need help on this one. Really did not want to resort to vise grips again.

I have a batch of 50/50 acetone and auto transmission fluid mixed already, some leftover from a few days back for freeing pistons on an old Honda. I'm going with the 50/50, man-oh-man that stuff did a JOB on freeing up the Honda 750, had been sitting 10 years, the final year was outside with the carbs off and the oil tank off, open to moisture. I could hardly believe it, this was after I'd doused it with PB for a day and got nowhere. This was the first time I'd used 50/50 atf/acetone, very impressed with it, and it's cheap too.

I'm relatively new to caliper rebuilds, and new to 50/50 atf/acetone too, thanks Patton would not have thought to use it.

If you can get the right fittings, a good hand pumped grease gun can create pressure the should move the stuck pistons.

MFolks wrote:

If you can get the right fittings, a good hand pumped grease gun can create pressure the should move the stuck pistons.

I can see that working -- the reason hydraulic systems work is that fluids, including grease, cannot be compressed very much at all and with a grease gun applying the pressure after having soaked the caliper in a penetrating solution it should pop 'em out.

There is a metric fasteners outlet near where I live, I'm wondering whether they'd have off-the-shelf metric plugs I could use to block off the hose connection on the caliper.

It seems like I could use the bleed nipple on the caliper as the grease gun fitting (connect the grease gun right to the bleed nipple) then all I'd need is a cap to block off the brake hose connection port.

Am I going in the right direction here?

Will likely find this thread most interesting.

Click here > kzrider.com/index.php?option=com_kunena&...d=5&id=184045#184096

Good Fortune!

I just popped some pistons out of some calipers that had been sitting out for 10 plus years... same issue - used 160psi air to pop em out... be careful and have something for them to charge into like a old tire or at least a big rag.

Injected wrote:

I just popped some pistons out of some calipers that had been sitting out for 10 plus years... same issue - used 160psi air to pop em out... be careful and have something for them to charge into like a old tire or at least a big rag.

Here are photos of the left half and right half of the rear caliper from my '78 kz1000a2.

The compressed air could work but there's an unthreaded brake fluid port in each half that can't be blocked off, so when I use my air gun the effect is limited by my ability to plug the unthreaded fluid ports with my thumb.

I suppose I could reassemble then use compressed air -- might try that after soaking the two halves of the caliper in 50/50 atf/acetone.

newOld_kz1000 wrote:

...compressed air could work but there's an unthreaded brake fluid port in each half that can't be blocked off, so when I use my air gun the effect is limited by my ability to plug the unthreaded fluid ports with my thumb.

I suppose I could reassemble then use compressed air -- might try that after soaking the two halves of the caliper in 50/50 atf/acetone....

Caliper reassembly is likely a necessary prerequisite regardless of method used in applying pressure in chamber behind pistons (i.e., air, grease, frozen water, whatever).

Otherwise, the open ports serve as pressure reliefs.

With pads removed (and rotor/disc absent), would put something soft between piston surfaces so the pistons won't collide directly against each other when they shoot out, especially if using air pressure.

Good Fortune!

Mine were slightly different... GPZ550, still you gotta block everything off and go in behind the piston thru the bleed hole to get it to pop out with air... need a BIG shop compressor.
If it has to be partially reassembled throw some thin strips of wood in there to soften the blow when they rocket out.

Okay, thanks, I'm gonna soak it, reassemble and put a wood block between the pucks, then try the compressed air, then grease gun if the air doesn't do it. Any idea on finding a functional grease gun fitting that will fit the bleed nipple threaded socket in the caliper?

newOld_kz1000 wrote:

Okay, thanks, I'm gonna soak it, reassemble and put a wood block between the pucks, then try the compressed air, then grease gun if the air doesn't do it. Any idea on finding a functional grease gun fitting that will fit the bleed nipple threaded socket in the caliper?

Reportedly, some grease guns fit right onto the existing bleeder nipple.

Regardless, must close fluid entry hole in caliper where hose feeds into with either an appropriate size bolt or a grease nipple.

If obtaining a new grease fitting, would prefer size that threads into the fluid entry hole, and leave the bleeder as is. Otherwise, obtain plug for hole and inject grease into bleeder.

And wouldn't dismiss otakar's soda/vinegar method, which seems an excellent suggestion.

Good Fortune!

I GOT BOTH PUCKS OUT (yay).

I got tired of waiting for the soaking to take effect so I tapped the left puck lightly with a hammer, put a vise grip on the outer rim, then put the vise grip into a vise and twisted the left half of the caliper and FINALLY got that puck to move.

Then I doused it with more penetrating oil, back in the vise grip + vise, then twisted and pulled it out. The point on the puck that was scuffed by the vise grip is only the indention where the rubber dust cover sits -- it won't affect the puck sealing at all.
Here are the picks showing it all. I used the exact same approach to extract the puck out of the right side of the rear brake caliper.