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Discussion Starter #1
Firstly the front master brake cylinder recall was 'taken care of' by a reputable local motorcycle shop.

This bike was purchased from a private seller this year, who had the front master recall done at said shop last year. Checked with the shop and they concurred, they replaced the master cylinder.

First day after 5 minutes of riding, the front brakes (left and right caliper) on their own begin applying pressure and slowed the bike to a stop mid corner with my wrist still trying to throttle. I pull over the best i can front brakes about fully locked, and the brake lever is stiff, completely not like it was moments before.
Called the seller and he walked me through how to release the brake pressure. (opening the bleeder valve nearest the master brake cylinder, squeezing the lever than re tighten the bleeder. Worked and it got me home.

Try riding the next day, same issue occurs. I bleed the brakes, and continue on riding the rest of the day brakes working as normal. I let the bike sit over night or possibly two and attempt to ride it again. i hear the brakes start to squeak, and the brakes start slowly applying pressure like it did before.
Did some research online, and attempt to change my brake fluid. went well, fluid was just as clear as the new stuff i'm replacing it with. bike sits over night, test it the next day and the same instance occurs.

Fast forward a few weeks, made an appointment at the same shop which is an hour away. Told them what I've done and that flushing it with my minimal tools didn't solve my problem. They flush the brake fluid with their tools, let the bike sit overnight and test it the next day. working fine. I show up a few days later to pick it up and we can hear the squeaking as he rolls it outside. They solved nothing. I asked if it could be some small piece of gunk lodging itself in a small hole in the master cylinder, and they said probably not it was replaced the year before.
Was not pleased and i drove it home. ( did a wheel to wheel inspection as well and they dropped the cost from $350 to $250) effing sweet deal
on the way out the mechanic suggested i try replacing the brake lines entirely, and if that doesn't work replace the calipers.

Well here i am today, i replaced the brake lines with steel lines with ones that are set up slightly different. Stock lines are rubber or whatnot, and the right line (longer line) runs down from the master cylinder and piggy backs with the left line at the right caliper. Than it travels around to the left caliper.
The new lines are steel and piggy back at the master cylinder, and run down to their respected calipers. I get them up to pressure and go for a test ride. Worked great, for 40 minutes.. The whole time i had been testing the brakes at multiple speeds, being ready for it to do it again. All seems good, get it up to 100mph and when i let off the throttle, the brakes are coming on harder than i've ever braked before at them speeds.


It has to be something wrong with the master brake cylinder right?
Something settles and clogs a small hole, and it acted crazy fast on my steel lines because they have no give when pressure occurs. When the lines were stock, they had give and took slightly longer and didn't brake nearly as quickly and hard.

And the switching of brake lines and new set up, doesn't that debunk the calipers being the issue theory?
they are both slowly seizing up in unison, i can feel equal heat on the discs when these instances occur.

I appreciate any of your thoughts on this, thank you Cheers
 

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Dreaming of buttsecks for years...
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Close up pic of your lever and MC.

What you're describing is due to fluid not being able to return to the reservoir. That is likely one of two things. 1) there's debris in the system blocking the port in the MC. 2) The MC piston is not returning to the fully extended position and blocking the port.

For #2, the usual cause is cheap levers.
 

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You should listen to me. No, seriously, listen to
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See this. Sounds like what you're experiencing.

"Called the seller and he walked me through how to release the brake pressure. (opening the bleeder valve nearest the master brake cylinder, squeezing the lever than re tighten the bleeder."

So he knew all about it when he sold you the bike and never mentioned it?

Except for testing, don't ride it until you get it fixed.
 

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Discussion Starter #6
Close up pic of your lever and MC.

What you're describing is due to fluid not being able to return to the reservoir. That is likely one of two things. 1) there's debris in the system blocking the port in the MC. 2) The MC piston is not returning to the fully extended position and blocking the port.

For #2, the usual cause is cheap levers.
I was also told by a separate mechanic that crud is most likely blocking the port in the MC. Seems to be the most logical reason behind the brake actions.
The MC is a Nissin, Japanese i believe, and the clutch lever if i had to guess came with it.

I'm a fresh new member, i cant post pics or links yet. laame.

BillV Sounds like what you're experiencing. "Called the seller and he walked me through how to release the brake pressure. (opening the bleeder valve nearest the master brake cylinder said:
He did know about it and didnt mention it. classy guy.
I will not ride it again until i get a new MC or clean it if possible. thank you brother
 

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You just lost $100 imaginary dollars good sir. not Chinese
That "mechanic" is a moron. You should get a refund for the work. If you take it in and they tell you "X" part requires replacement, is one thing, not fixing the issue and sending you along is another.

If you bled the system and bled it well, "crud" shouldn't be left in the system.

Before you go buy a new master, take the lever off and inspect the plunger and the plunger hole. Post pics.
 

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Discussion Starter #8


That "mechanic" is a moron. You should get a refund for the work. If you take it in and they tell you "X" part requires replacement, is one thing, not fixing the issue and sending you along is another.

If you bled the system and bled it well, "crud" shouldn't be left in the system.

Before you go buy a new master, take the lever off and inspect the plunger and the plunger hole. Post pics.
I brought it to them and asked them to not only try to solve the brake issue, but do a wheel to wheel inspection/ diagnosis and get a sticker. I wanted to know everything that was wrong with it that they could find. They charged me $250 after knocking $100 off the cost... I was pissed. Wasted a lot of time AND got a cracked windshield in my wrx on the ride home from my fiance one of the trips there.

I will give the plunger and plunger hole a check, thank you for the suggestion!

Will post pics when i get to 10 posts :serious:
 

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So, OP sent me a PM with pics. It's an OEM lever.

So if I had this bike on my lift table with this symptom, here's what I'd do (after visual inspection for the obvious problems):
1) Remove one caliper and try to push the pads apart. Only one place for the fluid to go. If could not, I would remove the lever and try again. It's possible something is wrong with the lever or assembly.
2) If I could push that caliper open, I'd reinstall, pump up the brakes and try the other caliper. It's possible there could be a line blockage.


You said it was both calipers. Are you 100% certain of that? The only facts I have now are that brake rub (a little is normal) is generating heat. The fluid is expanding due to heat and rather than returning to the reservoir is building pressure. What we don't know is why. I really don't think it's a stuck caliper. You'd have constant issues if it was. I highly doubt the OEM lever is the issue, but also don't know who installed the recall kit. It could possibly be the front brake switch holding the lever just slightly closed, or the lever just getting stuck on the pivot (the obvious problems I was referring to).

The sad truth is that brake systems are fairly simple. Any mechanic should be able to figure this out fairly quickly. If they can't, they should have their tools taken away.
 

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Discussion Starter #10
So, OP sent me a PM with pics. It's an OEM lever.

So if I had this bike on my lift table with this symptom, here's what I'd do (after visual inspection for the obvious problems):
1) Remove one caliper and try to push the pads apart. Only one place for the fluid to go. If could not, I would remove the lever and try again. It's possible something is wrong with the lever or assembly.
2) If I could push that caliper open, I'd reinstall, pump up the brakes and try the other caliper. It's possible there could be a line blockage.


You said it was both calipers. Are you 100% certain of that? The only facts I have now are that brake rub (a little is normal) is generating heat. The fluid is expanding due to heat and rather than returning to the reservoir is building pressure. What we don't know is why. I really don't think it's a stuck caliper. You'd have constant issues if it was. I highly doubt the OEM lever is the issue, but also don't know who installed the recall kit. It could possibly be the front brake switch holding the lever just slightly closed, or the lever just getting stuck on the pivot (the obvious problems I was referring to).

The sad truth is that brake systems are fairly simple. Any mechanic should be able to figure this out fairly quickly. If they can't, they should have their tools taken away.
Thank you for your run down on the matter appreciate it buddy!
I'm not 100% on if its both calipers, im just going by basic observations and feel with my fingers. It never happens when im close to my tools or garage of course, but i try to bring tools with me to get out of a bind every ride.
But during my test ride i wasnt using the front brakes so much i would think that they would be That hot. Ive never witnessed my discs that warm before, but then again i dont feel them after every random ride. not smokin but too hot to hold my hand on. The brake lever in the mean time is as stiff as a rock like you said due to pressure.

I agree with you, there are only a few components to the front brake system, this should be fairly simple for a mechanic to diagnose.
 

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Discussion Starter #11
Been doing more searching and reading through past threads on similar issues, and I apologize did forget to mention the bike has been tipped before. Which could mean something possibly got bent with the brake lever and or mbc causing said issue.
Sunday I should have time to tinker around with the lever and mbc, I'm going to get my hands on a o-ring remover tool and go to town and clean out the pig if she looks dirty, if nothing seems off with the brake switch or lever. Dont have much to lose if i muff it up, its not ride-able as it stands. Worse case im going to just get a brembo and replace both the mbc and the lever.. unless there are newer suggestions for replacement out there
 

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Able to put some tinker time in today. I took the right caliper off and noticed gunk right away inside the port where fluid comes into the caliper. And decided to break down the calipers completely and attempt to clean them out. I don't have a rebuild kit but i'm going to do my best and just clean everything. I also have just a tire compressor and not a real air tank with nuts so this might limit me to not getting out the second piston without bring it do my old mans garage. Will post pictures of the process below.
 

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Discussion Starter #14
Already slightly ahead of myself, should have cleaned it up before pumping out the pistons. The first one came out ok with my mini husky tire pump, but itll probably be impossible to get the second with what i got. I may remove the other side, clean it as well, than bring it to my Dads garage and pop the final pistons out. Potential road block till then.
 

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sprayed some cleaner into the hole at the bottom that leads into the second piston chamber, and flushed a bunch more of that orange gunk out.. Tried a little bit harder with my tire pump and finger to block the hole at the already removed piston chamber bottom, annnnnd pop! Oh my grossness.. (cover the Pistons with a rag when doing this for suuure)
 

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Are you saying that the snot we see was inside the caliper?
Yuup.. All of that gunk was trapped in the piston bore, not allowing the piston to go all the way in i presume.


Just went for a half hour test ride at 30-45mph, Leeeeeeanin back just in case haha. Fingers crossed test run #2 has positive results tomorrow.


Should i zip tie my brake lever engaged overnight?
 

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Discussion Starter #18
Post cleaning shots.
Once I got the hang of how to pop out the second piston, it was a piece of cake. Cleaning the surfaces took more time than disassembling and reassembling it seemed.
I coated the pistons and dirt seal rings with brake fluid before installing, and then cleaned up all surfaces real good once they popped back in.
 

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Discussion Starter #19
Second test drive, 10 minutes into the ride with constant brake checks, and pulling in the clutch to see if i felt resistance, the brake lever began to become stiff with my pads slowing me down. Pulled over, released the pressure through the top bleeder by the MC and putted home.
Drained the fluid, popped off the brake lever and pulled the plunger thing out. lil bit of grease but that's normal. seemed clean and easy to move abouts. Pulled out the piston cup set behind that, seemed okay, little stiff to push back inwards but normal i'm guessing. Clean.
Next i'm replacing the bleeder screws just in case.. After that i'm going to just replace the whole MC and lever with a Brembo.. If that still doesn't fix it than i'm going back into the calipers and replacing the pistons and rings. There wont be anything left to replace after that besides the calipers themselves. But they are clean as a whistle so i wouldn't think id have to
 

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Went ahead and replaced the 3 bleeder screws and new caps. Got the brake fluid to the correct level and went for a ride. And another, another... I'm at over a dozen 30+ minute rides and the brakes are working consistently normal.
I still don't believe it fully and am waiting for them to seize at any moments notice.
But I think we got it. Thanks for the help folks! Ride safe
 
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