MC piston stuck - now filling w/fluid

The piston on both my ZX550 master cylinders are both stuck in the full in position, probably from sludge. It's soaking in brake cleaner right now.

I hooked up a caliper directly too it and filled the lines with brake cleaner, and tried to activate it by pulling and pushing in the caliper piston, no action. Probably due to viscosity. I was thinking of trying it with brake fluid next.

Does any one know a good trick to free it?

Post edited by: godsjester71, at: 2006/09/19 09:48

My advice is to replace them. I don't mess around with brakes. REMEMBER..... If it don't run,NO problem. If it don't stop, BIG PROBLEM ! At a MINIMUM I would take them apart and inspect the bores,seals and pistons for problems. Cathy the cage driver is way more concerned about her cell phone and make up. You NEED brakes.:ohmy:

The viscosity shouldn't matter. The force is multiplied by the master cylinder, so you will need a lot of force to push it back with the caliper piston. Can you get a clamp on the caliper and push the piston in with it? Or bolt the caliper back on the fork and use a prybar to exert force against the piston. Be careful that you don't mar any of the metal surfaces.

godsjester71 wrote:

The piston on both my ZX550 master cylinders are both stuck in the full in position, probably from sludge. It's soaking in brake cleaner right now.

I hooked up a caliper directly too it and filled the lines with brake cleaner, and tried to activate it by pulling and pushing in the caliper piston, no action. Probably due to viscosity. I was thinking of trying it with brake fluid next.

Does any one know a good trick to free it?

If you have an air compressor, you can also try compressed air to push the piston out. Put a rag over the other end of the cylinder to catch any parts that might be forced out, then apply air pressure to the brake-line end of the cylinder using a trigger-operated valve. Wear safety goggles and make sure you do not have the rag-end of the cylinder pointed at your face!

OK, after talking around a bit, I'm borrowing one from a friend till winter, it's off a 96 Katana. This way I still have a fighting chance of having the bike sorted out enough to go on our Two Weeks After Labor Day ride to SW Wisconsin.

So word has it that chances are the cylinder could be scored, rendering the unit useless. I am going to take it apart to see, but most likely I will be buying an aftermarket later this year.

How to dismantle... A safe but rather messy way is to attach a grease pump (this is tricky, since my native tounge is Swedish... Grease pump is, I hope, a manual device for pressuring grease into things. Popular tool for tractor owners...) and let it do the work. The pros are that the piston won't shoot out and that it always work, since grease has high density. The cons... well, basically, it's greasy and takes some time to clean it up.

Or you just stick with the borrowed M/C...

Also known as grease gun locally

Actually went the lazy route:

eBay of course

Should be here in time for Rockerbox.

Post edited by: steell, at: 2006/09/19 18:16

OK, my brakes are going back together tomorrow on the ZX550, and i have to fill 4 different paths (anti--dive till I can get the pregressive springs this winter.

Are there any helpfull tricks to make my life easier or make sure they fill right?

One person told me to attach a hose to the bleeder and run the tube into a container of brake fluid, so it doesnt suck air back in somehow. Unreliable source tho.

Ive also been told to make sure the MC is ALWAYS full, that one makes sense.

Yes you can put the hose from the bleeder into a bottle with some fluid and it will work.

After reading this thread, I did what JMKZHI suggested and it has seemed to work best for me so far.

Excellent thread here

Post edited by: steell, at: 2006/09/19 18:17

godsjester71 wrote:

The piston on both my ZX550 master cylinders are both stuck in the full in position, probably from sludge. It's soaking in brake cleaner right now.

I hooked up a caliper directly too it and filled the lines with brake cleaner, and tried to activate it by pulling and pushing in the caliper piston, no action. Probably due to viscosity. I was thinking of trying it with brake fluid next.

Does any one know a good trick to free it?<br><br>Post edited by: godsjester71, at: 2006/09/19 09:48

carefull with that brakeclean,it does terrible things to rubber parts !

Are you guys doing this with just one caliper? With four, i can see this being a royal PIA, bubbles (crud in the case of the anti dive) flowing thru the top lines each time.