master cylinder problem
Thread Starter
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Cruiser
Joined: Oct 2008
Posts: 234
Likes: 15
From: Southern California
master cylinder problem
working on a 1991 FXSTC.
My brakes were working fine originally. I changed my handle bars and needed to switch to shorter brake lines. I've done this on several bikes before with no issues. After I hooked everything up I filled up the master cylinder and start to try and bleed the brakes. I pump the brake lever several times and no fluid comes out of the bleeder. Turns out the fluid isn't even leaving the reservoir. I tried with a vacuum pump at the bleeder screw and nothing. I tried fulling the system from the bleeder with a syringe and I can't get anything into the lines. I disconnected the line to make sure that's not the problem and fluid flows fine it.
So, I get a master cylinder rebuild kid and put that in. I put everything together and it's doing the same thing. It's like something is blocking the fluid from flowing from the reservoir. I cleaned everything out and check to make sure none of the holes were obstructed.
I've taken it apart and put it together over and over and now I'm getting the same result. As soon as I reassemble, I can push fluid up the line from the bleeder into the reservoir. Then I pump the lever once and it feels almost stuck. If I squeeze the lever past that sticking point it goes slack and the reservoir goes back to being "blocked" and no more fluid can be pushed up from the bleeder.
Any suggestions?
My brakes were working fine originally. I changed my handle bars and needed to switch to shorter brake lines. I've done this on several bikes before with no issues. After I hooked everything up I filled up the master cylinder and start to try and bleed the brakes. I pump the brake lever several times and no fluid comes out of the bleeder. Turns out the fluid isn't even leaving the reservoir. I tried with a vacuum pump at the bleeder screw and nothing. I tried fulling the system from the bleeder with a syringe and I can't get anything into the lines. I disconnected the line to make sure that's not the problem and fluid flows fine it.
So, I get a master cylinder rebuild kid and put that in. I put everything together and it's doing the same thing. It's like something is blocking the fluid from flowing from the reservoir. I cleaned everything out and check to make sure none of the holes were obstructed.
I've taken it apart and put it together over and over and now I'm getting the same result. As soon as I reassemble, I can push fluid up the line from the bleeder into the reservoir. Then I pump the lever once and it feels almost stuck. If I squeeze the lever past that sticking point it goes slack and the reservoir goes back to being "blocked" and no more fluid can be pushed up from the bleeder.
Any suggestions?
Seasoned HDF Member
Joined: Mar 2010
Posts: 21,150
Likes: 7,662
From: Poolville
Sounds like the master cylinder is still air bound... Remove the brake line and bleed the cylinder first then reattach the line (after you back fill) or completely raise the line and caliper above the master cylinder as to not let any air back into master...
Road Warrior
Joined: Jul 2016
Posts: 1,370
Likes: 439
From: va
Speed Bleeders are a big help
Thread Starter
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Cruiser
Joined: Oct 2008
Posts: 234
Likes: 15
From: Southern California
I've got the brake line disconnected from the master cylinder. The reservoir has fresh fluid in it. When I pump the lever I can feel air pressure coming out of the hole where the brake line would connect. When I release the lever I can feel suction on my finger. Even if I pump the lever several times, the fluid from the reservoir, isn't moving down.
Road Warrior
Joined: Jul 2016
Posts: 1,370
Likes: 439
From: va
OK -- make your finger act like the bleeder screw --- as put your finger over the hole -- pump lever 2 to thee times keep a little pressure on lever --release your finger for just a split second --hold finger over hole --pump lever --hold lever --release finger , until you have pressure build up on lever then release finger and hook up line , bleed the rest of the system
The rest of the system WILL take a while to push air down hill -- be patient it will work
Speed Bleeders are GREAT to use
The rest of the system WILL take a while to push air down hill -- be patient it will work
Speed Bleeders are GREAT to use
Thread Starter
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Cruiser
Joined: Oct 2008
Posts: 234
Likes: 15
From: Southern California
I've tried it with the cover on and off...same result.
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Thread Starter
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Cruiser
Joined: Oct 2008
Posts: 234
Likes: 15
From: Southern California
OK -- make your finger act like the bleeder screw --- as put your finger over the hole -- pump lever 2 to thee times keep a little pressure on lever --release your finger for just a split second --hold finger over hole --pump lever --hold lever --release finger , until you have pressure build up on lever then release finger and hook up line , bleed the rest of the system
The rest of the system WILL take a while to push air down hill -- be patient it will work
Speed Bleeders are GREAT to use
The rest of the system WILL take a while to push air down hill -- be patient it will work
Speed Bleeders are GREAT to use
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Thread Starter
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Cruiser
Joined: Oct 2008
Posts: 234
Likes: 15
From: Southern California
I still can't get any fluid to come out of the master cylinder. it's just sitting in the reservoir. I feel air pressure on my finger when I pump the lever. But no matter how many times I pump the lever it is stays slack and doesn't push any of the fluid down from the reservoir.
I've dealt with bleeding brakes several times and run into problems with air trapped in the lines and soft brakes. But I've never dealt with brake fluid that refused to leave the reservoir
I've dealt with bleeding brakes several times and run into problems with air trapped in the lines and soft brakes. But I've never dealt with brake fluid that refused to leave the reservoir
Last edited by das56170; Jul 23, 2017 at 04:58 PM.
Road Warrior
Joined: Dec 2015
Posts: 1,416
Likes: 317
From: CA
I suspect air rather than blockage but could need rebuild.
Simplest thing to start with - I would use an " " or a Mityvac style break bleeder pump to get it started. Clear all the old oil out while keeping fresh oil topped up.
The suction gun is a multi-tasker and thus superior to the mightyvac (though its gauge is worth a mint when you need one). I think I use a 3/8 tube to step down the large clear tube on the suction gun tube to brake bleeder level.
Makes the job fast and excellent for rear brakes which are typically not elevated and thus no gravity hydraulic action. Works great for front brakes due to speed.
After flush, then bleed.
Simplest thing to start with - I would use an " " or a Mityvac style break bleeder pump to get it started. Clear all the old oil out while keeping fresh oil topped up.
The suction gun is a multi-tasker and thus superior to the mightyvac (though its gauge is worth a mint when you need one). I think I use a 3/8 tube to step down the large clear tube on the suction gun tube to brake bleeder level.
Makes the job fast and excellent for rear brakes which are typically not elevated and thus no gravity hydraulic action. Works great for front brakes due to speed.
After flush, then bleed.