Brakes locking up, help!
Seasoned HDF Member
Joined: Dec 2005
Posts: 19,830
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From: poway
Sounds like you need a G string!!
I had this happen on an old street bike that sat for a long time. Flushed everything then went on a ride, within 5 mi. The Front would start to lock, only way to free it up was release the pressure at the caliper.
I'll save you 3 months of work. Because that how long it took me to figure it out. Pop the cap on the master cylinder (take all precautions to protect all surfaces from drips and slashing fluids) anyways, you can see the plunger (piston) that forces the fluid in the line. Well just close to it, you will see a tiny hole, that is a bleed path. It sounds like it's plugged. Take a G-string from a guitar. Stick it in the hole, it should pass down to the bottom. (Mine was about 3/4" deep) you can tell when you bottom out. Anyways. If it's plugged it will only go in just a couple mm.
Btw I use a g string from an electric guitar from a standard size 10. If someone plays the guitar in your house, you only need a short piece
Within that pack the G sting is a size 17
I had this happen on an old street bike that sat for a long time. Flushed everything then went on a ride, within 5 mi. The Front would start to lock, only way to free it up was release the pressure at the caliper.
I'll save you 3 months of work. Because that how long it took me to figure it out. Pop the cap on the master cylinder (take all precautions to protect all surfaces from drips and slashing fluids) anyways, you can see the plunger (piston) that forces the fluid in the line. Well just close to it, you will see a tiny hole, that is a bleed path. It sounds like it's plugged. Take a G-string from a guitar. Stick it in the hole, it should pass down to the bottom. (Mine was about 3/4" deep) you can tell when you bottom out. Anyways. If it's plugged it will only go in just a couple mm.
Btw I use a g string from an electric guitar from a standard size 10. If someone plays the guitar in your house, you only need a short piece
Within that pack the G sting is a size 17
Welding tip cleaner or even a bristle from a wire brush should clear it out..
There might be something wrong with the new brake line. Something caught in it that is acting like a one way valve also but the issue seems to be the master cylinder.
Road Captain
Joined: Nov 2016
Posts: 666
Likes: 95
From: Berlin
Yep +1 on above, the gstring sounds the way forward, after that reflush with new fluid, because if the pads have heated up the rotor the fluid would have boiled.
Outstanding HDF Member
Joined: Dec 2012
Posts: 2,557
Likes: 235
From: Texas
sounds like a classic master cylinder failure...2500 miles on a four-year old bike suggests that it is parked more than rode and those gaskets and seals deteriorate and brake fluid collects crud that settles in the bottom of the reservoir and sooner or later the crud stops up the vent hole and you get problems.
I'm thinking that just cleaning out the hole is a band-aid fix at best because whatever crud is in the bottom of the reservoir that got stirred up and clogged the vent hole in the first place is still there and it will eventually happen again.
When this has happened to me (twice now), I get an OEM rebuild kit and a couple of banjo washers for around $30 and rebuild it...and for around $50 more I can rebuild the caliper at the same time and flush out the line and change out the fluid and be good to go knowing my brakes are gonna work because the job was done right. Some folks may think this is overkill, and they maybe right for them, but it is not a big job or expensive and front brakes are pretty important to me...better knowing for sure than guessing and assuming...
I'm thinking that just cleaning out the hole is a band-aid fix at best because whatever crud is in the bottom of the reservoir that got stirred up and clogged the vent hole in the first place is still there and it will eventually happen again.
When this has happened to me (twice now), I get an OEM rebuild kit and a couple of banjo washers for around $30 and rebuild it...and for around $50 more I can rebuild the caliper at the same time and flush out the line and change out the fluid and be good to go knowing my brakes are gonna work because the job was done right. Some folks may think this is overkill, and they maybe right for them, but it is not a big job or expensive and front brakes are pretty important to me...better knowing for sure than guessing and assuming...
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Novice
Joined: Sep 2017
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From: Nl
I would agree with this.. There are 2 holes in the master cylinder that feed the piston that generates the pressure.. The small one is likely plugged. The small one is uncovered by piston cup and lets the pressure in the line drop. If it's plugged, as the brakes heat up the fluid expands and needs to escape from the line and back into the master cylinder. If it don't brakes will start to engage. Not sure why popping the reservoir cover stops the issue, could simply be time to let pressure drop or it is somehow involved in the blockage.
Welding tip cleaner or even a bristle from a wire brush should clear it out..
There might be something wrong with the new brake line. Something caught in it that is acting like a one way valve also but the issue seems to be the master cylinder.
Welding tip cleaner or even a bristle from a wire brush should clear it out..
There might be something wrong with the new brake line. Something caught in it that is acting like a one way valve also but the issue seems to be the master cylinder.
Sounds like you need a G string!!
I had this happen on an old street bike that sat for a long time. Flushed everything then went on a ride, within 5 mi. The Front would start to lock, only way to free it up was release the pressure at the caliper.
I'll save you 3 months of work. Because that how long it took me to figure it out. Pop the cap on the master cylinder (take all precautions to protect all surfaces from drips and slashing fluids) anyways, you can see the plunger (piston) that forces the fluid in the line. Well just close to it, you will see a tiny hole, that is a bleed path. It sounds like it's plugged. Take a G-string from a guitar. Stick it in the hole, it should pass down to the bottom. (Mine was about 3/4" deep) you can tell when you bottom out. Anyways. If it's plugged it will only go in just a couple mm.
Btw I use a g string from an electric guitar from a standard size 10. If someone plays the guitar in your house, you only need a short piece
Within that pack the G sting is a size 17
I had this happen on an old street bike that sat for a long time. Flushed everything then went on a ride, within 5 mi. The Front would start to lock, only way to free it up was release the pressure at the caliper.
I'll save you 3 months of work. Because that how long it took me to figure it out. Pop the cap on the master cylinder (take all precautions to protect all surfaces from drips and slashing fluids) anyways, you can see the plunger (piston) that forces the fluid in the line. Well just close to it, you will see a tiny hole, that is a bleed path. It sounds like it's plugged. Take a G-string from a guitar. Stick it in the hole, it should pass down to the bottom. (Mine was about 3/4" deep) you can tell when you bottom out. Anyways. If it's plugged it will only go in just a couple mm.
Btw I use a g string from an electric guitar from a standard size 10. If someone plays the guitar in your house, you only need a short piece
Within that pack the G sting is a size 17
Road Captain
Joined: Jul 2008
Posts: 613
Likes: 33
From: East Alton, IL
The return hole in the MC is called the "spooge" hole and it's plugged. It is a very tiny hole and easily overlooked. Anything you did with the lever isn't going to help the original problem of brakes locking up.
It's not a big deal to clean that hole. I'm surprised the "Mechanic" you told to flush the system didn't check that especially after hearing your problem. Now if you didn't mention the brakes locking up he would not check it. I'm further surprised he didn't test ride the bike after his work. The problem would have surely showed up and he should have addressed it at that time.
Go to a local music store and ask for the #10 guitar string. It's probably only about $2. I use a #80 micro drill bit in a pin vise to clean return or spooge holes.
It's not a big deal to clean that hole. I'm surprised the "Mechanic" you told to flush the system didn't check that especially after hearing your problem. Now if you didn't mention the brakes locking up he would not check it. I'm further surprised he didn't test ride the bike after his work. The problem would have surely showed up and he should have addressed it at that time.
Go to a local music store and ask for the #10 guitar string. It's probably only about $2. I use a #80 micro drill bit in a pin vise to clean return or spooge holes.
Seasoned HDF Member
Joined: Dec 2005
Posts: 19,830
Likes: 7,968
From: poway
So, I have thoughtof a probable cause. Let me know if you think it's the case... When I installed the bars and had the brakes and switch console off the bar, apparently the tip on the "brake light" plunger broke. I was aware this happend and my fix so that the brake lights would disengage was to wrap some black tape around the lever. It fixed the light issue but the tape on the backside of the lever was preventinf the master cylinder plunger from fully opening up.. (just a hair) I'll know later today if it worked... fingers crossed!! What do you guys think?
Seasoned HDF Member
Joined: Jan 2015
Posts: 15,947
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From: Sandy Eggo's North County
Are you using the exact lever that came with that M/C? I had the same issue years ago on a different bike. It turns out the lever push blade wasn't correct for the M/C. It wouldn't let the pressure bleed back fluid into the res.
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Novice
Joined: Sep 2017
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Likes: 0
From: Nl
The return hole in the MC is called the "spooge" hole and it's plugged. It is a very tiny hole and easily overlooked. Anything you did with the lever isn't going to help the original problem of brakes locking up.
It's not a big deal to clean that hole. I'm surprised the "Mechanic" you told to flush the system didn't check that especially after hearing your problem. Now if you didn't mention the brakes locking up he would not check it. I'm further surprised he didn't test ride the bike after his work. The problem would have surely showed up and he should have addressed it at that time.
Go to a local music store and ask for the #10 guitar string. It's probably only about $2. I use a #80 micro drill bit in a pin vise to clean return or spooge holes.
It's not a big deal to clean that hole. I'm surprised the "Mechanic" you told to flush the system didn't check that especially after hearing your problem. Now if you didn't mention the brakes locking up he would not check it. I'm further surprised he didn't test ride the bike after his work. The problem would have surely showed up and he should have addressed it at that time.
Go to a local music store and ask for the #10 guitar string. It's probably only about $2. I use a #80 micro drill bit in a pin vise to clean return or spooge holes.
If you are limiting the return of the master cylinder piston to it's home position, there is a strong possibility that the small hole blocked by the piston and the brake lines can't release the line pressure. The brake fluid does not need to boil but simply expand due to heat to cause the brake drag.. Simply using the brakes can cause enough heat.
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Seasoned HDF Member
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From: Sandy Eggo's North County
Originally Posted by Nlstreetbobber
So, I have thoughtof a probable cause. Let me know if you think it's the case... When I installed the bars and had the brakes and switch console off the bar, apparently the tip on the "brake light" plunger broke. I was aware this happend and my fix so that the brake lights would disengage was to wrap some black tape around the lever. It fixed the light issue but the tape on the backside of the lever was preventinf the master cylinder plunger from fully opening up.. (just a hair) I'll know later today if it worked... fingers crossed!! What do you guys think?
Last edited by NORTY FLATZ; Oct 9, 2017 at 12:51 PM. Reason: darn phone graphics...
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