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rear brake not bleeding - rebuilt master cylinder

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Fluid is being pushed out of the rear master cylinder where the line attaches to it but when I put the line on, it doesnt want to push the fluid through the line.

 

I have a vacuum pump here and spent quite a bit of time trying to get the fluid to come through and it wont, at all. Even held the brake lever down too.

 

What am i doing wrong??

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At this point I would remove the brake line from the caliber & master cylinder and attempt to blow compressed air through the line. If that checks out, blow compressed air through the feed hole on the caliper with the bleeder screw open to make sure that air will pass through the caliper as well. If both check out, then you know the problem is in the master cylinder itself. You indicated that you are getting fluid OUT of the master cylinder so it's probably the line is plugged/collapsed internally, or the caliper has a blockage of some sort (though not likely). 

 

Please post back and let us know what the problem was.

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Try taking the bleeder screw all the way out of the caliper and blowing air through it. I have had dirt get in that bleeder screw which did not allow fluid to bleed out. Then reinstall and try again. I'm pretty sure your going to find the problem in the bleeder screw itself. You would have to get a pretty big piece of dirt in your brake line for it to be clogged.

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Try feeding fluid into the bleeder with a syringe.

 

i tried this initially and all it did was leak out from the tube and threads. maybe it is the line..hmmm :devil:

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At this point I would remove the brake line from the caliber & master cylinder and attempt to blow compressed air through the line. If that checks out, blow compressed air through the feed hole on the caliper with the bleeder screw open to make sure that air will pass through the caliper as well. If both check out, then you know the problem is in the master cylinder itself. You indicated that you are getting fluid OUT of the master cylinder so it's probably the line is plugged/collapsed internally, or the caliper has a blockage of some sort (though not likely). 

 

Please post back and let us know what the problem was.

 

So i took the line off today and bought some needles for the syringe (from tractor supply co) and injected the brake fluid directly into the pin hole into the line, fluid is going through it just fine.

 

I hooked up the vacuum pump to the bleeder on the caliper and put my thumb over the hole where the line goes, and it lifted it after i pumped it up, it sucks air through just fine..

 

when i pump the lever with the brake line off, fluid shoots out of the master cylinder where the line goes ..

 

i dont know &%$#@! im doing wrong.

Edited by nj_wrx_rider

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Ok. When you are using the vacuum pump, is it holding vacuum? If it is then there is a restriction somewhere. Possible dirt in the bleeder screw? Disconnect the line from the master cylinder. Place your thumb over the outlet threads to block the fluid coming out. Apply a good amount of pressure with the thumb and pump the pedal at the same time. If it starts pushing your thumb off and fluid comes out with some pressure, the master is good.

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Don't pump it. Press it down once and hold it then crack the bleeder. repeat 5-6 times. I did my brakes the other day and pumping just aerated the fluid and if your starting with zero fluid it could be your problem. I pumped for an hour used half a bottle of fluid before my neighbor came over and let me in on that little secret.

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Ok. When you are using the vacuum pump, is it holding vacuum? If it is then there is a restriction somewhere. Possible dirt in the bleeder screw? Disconnect the line from the master cylinder. Place your thumb over the outlet threads to block the fluid coming out. Apply a good amount of pressure with the thumb and pump the pedal at the same time. If it starts pushing your thumb off and fluid comes out with some pressure, the master is good.

 

yes, i should note that i did reverse fill the caliper with fluid and was able to pull the fluid out of the caliper with the vacuum bleeder. the fluid never managed to work its way back up to the master cylinder

 

 

Don't pump it. Press it down once and hold it then crack the bleeder. repeat 5-6 times. I did my brakes the other day and pumping just aerated the fluid and if your starting with zero fluid it could be your problem. I pumped for an hour used half a bottle of fluid before my neighbor came over and let me in on that little secret.

 

ill give this a try, thanks.

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Spin your tire wheel while pumping the brake.

 

That seemed to make a difference when I bled my brakes.

 

the cylinder is compressed all the way into the caliper -_-

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Sounds to me that your rebuild did not work out. Is there another bike that you could attach it to? Or another caliper? I read some where that you can tie the brake pedal off on something and leave it overnight and it will pressurize the system. The caliper does need to be lower than the master cylinder and the line where it attaches to the caliper needs to be higher than the bleed screw. I would put it all together on a bikestand with the rear tire touching the ground and the front a few inches off. Fill the reservoir leave the cap off, get a piece of wire and tie a tube onto the bleed screw with it cracked, push as much fluid as you can into from there. Then try the bleed procedure again remember only one pump, hold and crack, then tighten and repeat. If none of this works you either have a leak somewhere that's not allowing pressure to build or the rebuild went wrong somewhere. The cylinder in the caliper should be pushed in all the way. Why did you rebuild the master if you don't mind me asking.
 

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Here's 1 last idea to try.. With the brake line connected to the caliper but disconnected from the brake master cylinder, try and put a rubber tipped air nozzle to the feed hole on the line. If the caliper pistons extend from the caliper itself, and the brakes apply, then you know the problem is in the master cylinder.

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