New brake system but piston won't move

scotts

We recently purchased a slimline master cylinder, part #08-4003, from MIkesXS. It lists this m/c for use with stock, single disc brakes.
We installed it with a new braided one-piece hose and a rebuilt stock caliper. We were unable to get the piston to move on the caliper. We can get fluid to and into the caliper and out of the bleed valve, but the piston would not move.

There were some minor pits on the piston so we ordered a new caliper from MikesXS. With it installed we get the same thing. Fluid all through the system but the piston will NOT move. Could the master cylinder be defective?

Also, the website description says this m/c has no threaded holes for a mirror, yet the one we received has threaded holes. I'm wondering if we have the correct cylinder for our application. This is an 11mm piston, vs. 12.9 or 13.0 for stock, but that shouldn't make a difference, right? And like I said, it's listed for use on stock bikes/brake systems.

Inside the resevoir of the m/c is: Z2098, if that means anything.

Any thoughts as to why the brakes won't work or the m/c won't move the piston?

gordo

The bore size DOES make a difference, esp. when it come's to how much movement is needed to apply the piston to the pad. You did not state that if you have a solid lever or not. From my observation's, your not getting any resistance at the lever. You need to build up a 'reserve pressure' to get a good solid 'feel' at the lever. How to do that is to 'pump' the lever slowly in & out until you feel the resistance building up.DO NOT open the bleeder until you get resistance!!! Once you get the resistance, then bleed normally, but DO NOT keep the bleeder open & bottom the lever.Go about 3/4 of the way & close the bleeder. Then start all over again. When your sure all the air is out of the system, the piston should be in contact with the pad/disc. Once that has been achieved, the brake will function normally. Very little movement of the piston is needed from full 'on', to full 'release'.

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Yamaha xs650