Just rebuilt rear master cylinder and not getting any pressure

Joined
Mar 20, 2011
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La Crescent, Minnesota
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2005 ST1300
Installed Honda OEM rear master cylinder and try as i may...cannot get any pressure/vacuum. There are speedbleeders at the calipers. Is there some "trick" to get a prime inorder for the master cylinder to build pressure?

any insight appreciated,
Jay
 
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One thing I would mention is to crack the speedbleeders 1/4 turn only. Turning it out too far will allow air to be sucked in past the bleeder threads.
 
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If you had a vacuum brake bleeder, now would be the time to put it to use. My guess is you have an airlock in the master cylinder, so you need to pull some fluid through to move that air. Otherwise if the brake line was full to the caliper, you could push the caliper piston back to push fluid back through the master to push the air out.
 

DJDixon

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There was a post earlier from someone that said that even with the mighty vac they couldn't get it to bleed the system until they put an original bleeder screw in. Once the pressure was restored, they were able to put the speed bleeder back in and bleed normally. I'm guessing the speed bleeders won't pass air.
 
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Peoria, Illinois
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Before you get another tool which you should be able to get by without... If you remove the banjo bolt from the master, try pouring a bit of brake fluid in the piston area, and cover it with your thumb. You should be able to feel pressure/suction and then it'll shoot fluid after just a couple of pumps. Verify the master is working first.
 
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8901
Before you get another tool which you should be able to get by without... If you remove the banjo bolt from the master, try pouring a bit of brake fluid in the piston area, and cover it with your thumb. You should be able to feel pressure/suction and then it'll shoot fluid after just a couple of pumps. Verify the master is working first.
He that dies with the most tools wins!

I have found many uses for a vacuum bleeder, other than bleeding brakes. Great for starting a fuel siphon, checking vacuum gauges etc.
 
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There's nothing wrong with a vacuum tool, I just don't think he needs to get it yet based on the little info we have on the problem. We don't even know if the master cylinder is primed and/or putting out any fluid by itself.
 
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If you use a vacuum bleeder, you can suck fluid through the master cylinder and displace any air that is in there. I suspect the only reason that the system can't get pressure is a lack of fluid in the cylinder area.
 
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Put the OEM bleeder screw back on and try "reverse bleeding" - using a syringe ( with a small diameter hose attached between the syringe & bleeder ) , force brake fluid from the bleeder to the MC. Then remove the syringe and hose, and let gravity do some of the bleeding.
 

lomita

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With the speed bleeder cracked half a turn out, and a piece of clear tubing, it is easily seen what action is occurring upon cylinder actuation, i.e., air or fluid traveling through the line. Course if there is no pressure, perhaps the seal is in facing the wrong direction.

I just got a kit today with the wrong seals, spring, and piston. One step forward, two steps back. What rebuild kit are you using?
 
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You may have an air bubble at the banjo fitting at the Master Cylinder. You can crack open the banjo fitting and bleed the bubble out at that spot. Another helpful tip... get a clamp and lightly compress the brake line just enough to stop the flow... do this about 3 inches from the master cylinder and check if you have pressure (after bleeding the banjo fitting). If you have pressure, keep sliding the clamp down the line until you get to the split block. Pressurize the line, release the clamp, then reclamp.... repeat while bleeding the calipers. This procedure works well to prevent air in the system from backing up in the lines.
 
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