Master cylinder fails to pump

If you can't pump fluid in with the syringe then there is some sort of blockage. The entire system is just a straight shot from the calipers to the MC. If you are certain the the bleeder valve is open and will allow fluid to pass through it, then I would start with loosening the banjo fitting at the caliper and using the syringe see if you can pump fluid to that point, and work your way up the line until you find the blockage.

 

You stated earlier that the lines were clear in your first post. Try removing the brake line from the master cylinder and press your thumb over the opening in the master cylinder and pump the handle, if you get no pressure build up it is your master cylinder failing. If your master cylinder passes, replace the brake line and fill the master cylinder. Remove the brake line from the caliber and then clamp the brake handle in the open position like if you were braking. If brake fluid passes after an hour or two, then your caliber/bleeder screw needs to be serviced. If not, you have developed a clog in the lines and or banjo bolts.

 

This happens a lot more often than people realize...........

 

okay say I have a bleeder screw plugged up, how large of a hole needs to be in the bleeder screw to allow fluid to go through? i try to blow my breath through the bleeder screw (yes I put the bleeder screw in my mouth!) and its very difficult to pass anything. master cylinder does push air, I put my lips onto the opening (yes you read that right, my lips! its too cold for my fingers to feel anything) and felt a slight push of air onto my lips.

 

waltz on down to your napa store and get some new ones for about a buck each.
wrap the threads with teflon tape but keep the hole clear

 

^^^^^ do that ^^^^ it works. Actully you can probably get any air out just by cracking the banjo fitting at the MC and bleeding the MC normally. The angle of the MC on the Maxim bars lends itself to trapping air at the banjo fitting.

 

okay I have pumping action with the master cylinder and the bleeder valve has been fixed. got the air out of the hoses and I can pump my master cylinder, replenish it before completely going empty several times, and yet I never get pressure to pump the brakes! what is going on?? As soon as I fix one thing, another thing always comes up...If all the air is out of the lines wouldn't the pumping cause the cylinder piston in the brake caliper to start moving? I have zero brake action movement

Edit: already done the idea of cracking the banjo bolt near the MC with slight pressure on the lever to push any last air out near the MC. also I already done the reverse bleeding by opening the bleeder valve and pushing fluid up the system into the MC - doing this produces no air bubbles so one would think I have all the air out of the system! I don't know what else would cause no pressure buildup to pump the brakes... help please

 

you still have air trapped in the system. think like a bubble, it always goes up until it gets stuck somewhere, wheel cyl/fitting/splitter/loop in the hose. move things around so if there were a bubble there it has a way to go up the line. then pump it a few times and quit, by morning the air should be at the master.

 

Did you try tying the brake lever when you tried to push the fluid in with the syringe?

 

the brake system is essentially a one way valve with a relief, with the caliper bleeder open and no lever pulled fluid can just free flow. There's two holes inside the piston chamber, when you pull the lever one internal hole gets blocked by one of the piston seals forcing fluid out the second hole down to the caliper, when you release it the built up pressure is what returns the fluid back in the other, if one of the holes inside the piston chamber is blocked, fluid will fight to get back inside the master cylinder. If this happens you will have a slow return on caliper piton or sometimes almost not at all. Also, if you only move a small amount of fluid, and the caliper piston will not return. Then you most likely have air in the system. the master cylinder will pump anything (fluid/Air)... when you pull the lever does it bottom out, and/or have slight pressure and spongy? bottoming out says your master has air in it still, spongy says your pushing some fluid but not enough indicating the same issue.

Air bubbles rise, but not in all cases as noted above by a member noting the banjo bolt mounting position, and or the way the master mounts to the bars... you need to adjust the position of all component's so any air inside has no "Pockets" it can hide in while fluid passes right by it. once you have good brake fluid flow and pressure you can reposition them back to riding position. and he was correct by saying to turn the bars all the way to the left, this puts the reservoir in a more level position and at its highest point. Even reverse, or vacuum bleeding will not guarantee all air is out of the system, you may need to giggle lines or take a rubber hammer tapping on side of master cylinder, or dismount any etc.... no one has said the bike make that I have seen, does it have dual calipers with a center joint (proportioning valves)? I have had two tiny air bubbles make an entire lever pull feel so spongy the piston barely moved.

do this, fill reservoir up, put a clear hose onto bleeder long enough to have an arch curve and hang it above the caliper, open bleeder. and let it set for 1 minute, while you watch it. see any bubbles? It should gravity bleed by its self, and fluid should start to flow, because the master cylinder piston has not been pulled past the relief hole. the reason for the arching hose is to allow fluid into hose, letting air rise past it but still keeping fluid in hose right at the bleeder preventing bubble from being pulled back into it. Now pump (pull) lever, several times, you should see fluid move in and out. if a bubble/s come out hold lever position till bubble rises in hose and only fluid can be pulled back in. Now pull the lever and hold it, now close the bleeder and release the lever. you should see reservoir fluid level drop. repeat this several times till no more bubbles are seen coming into tube.