Brake Bleeding Help

"TheJWT" (thejwt) 03/27/2020 at 14:19 • Filed to: None

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This is an old picture, the rear caliper is hooked up again.

I’m trying to bleed the rear brake on my motorcycle, and I’m having an odd problem. For some reason, brake fluid is going into the master cylinder just fine (I made sure there wasn’t a clog in the line coming from the reservoir), but nothing comes out. I pumped the brake a few times and held it down and completely removed the banjo bolt going directly in to the cylinder, but nothing came out at all. I tried this probably 10 times and no luck.

The master cylinder was pretty much dry as it had been off the bike for a while and I feel like that’s causing the problem, but I can’t seem to find how to fix it. It’s worth noting that it did work fine when I took it off the bike, and it hasn’t been taken apart or anything. I was thinking maybe a vacuum bleeder would work to suck fluid through it, what do you all think?

kanadanmajava1 > TheJWT 03/27/2020 at 14:27

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Maybe the master cylinder piston is  stuck at the bottom ? 

PartyPooper2012 > TheJWT 03/27/2020 at 14:32

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Does the master cylinder move freely? Is anything leaking out of the master cylinder - like onto the ground?

Maybe it’s super dry and wants to soak in some of that good DOT fluids

WasGTIthenGTOthenNOVAnowbacktoGTI > TheJWT 03/27/2020 at 14:32

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did you bench bleed the master cylinder?

PartyPooper2012 > TheJWT 03/27/2020 at 14:33

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oh... just a random question. I am sure you’re doing it right, but you are pouring fluid into rear reservoir, not the one around steering handlebars?

McMike > TheJWT 03/27/2020 at 14:39

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Oooh, FZR?

You already started taking it apart by removing the hose from the caliper. Keep going. Take off the brake hose, and then see if you can pump fluid out of the MC.

TheJWT > PartyPooper2012 03/27/2020 at 14:49

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It does move freely and no leaks, it feels like there’ s some fluid in there because when I press the brake down it springs back up.

That could be true, I left the reservoir full and I’m going to try again this evening...

TheJWT > McMike 03/27/2020 at 14:50

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Yep, 600! That’s what I’ve been trying, nothing comes out of the MC

TheJWT > kanadanmajava1 03/27/2020 at 14:50

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Maybe a dumb question, but how would I check if that’s the case?

TheJWT > PartyPooper2012 03/27/2020 at 14:51

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Yes haha, the front reservoir has its own set of issues with stripped sc rews that i’m dreading fixing

TheJWT > WasGTIthenGTOthenNOVAnowbacktoGTI 03/27/2020 at 14:52

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No, I was wondering about that... I’m not entirely sure how to do it but I’ll do some research

Michael > TheJWT 03/27/2020 at 15:21

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Did you try hitting it with a hammer?

kanadanmajava1 > TheJWT 03/27/2020 at 15:36

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If you remove some connection between the slave and the master cylinder but the fluid doesn’t escape on the floor the system is blocked. The bottomed piston blocks the whole system. There’s also the possibility of collapsed rubber hose. It’s rare situation but it d oe s happen too. If you can next open the connector going out from the master cylinder you could figure out which is the case.

McMike > TheJWT 03/27/2020 at 15:40

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Oh, I missed that details . I saw the hose in the photo and thought it was still attached.

Your MC might need to be rebuilt/replaced.

Your eyes do not like brake fluid, especially brake fluid under pressure that is released when you least expect it.  :)

WasGTIthenGTOthenNOVAnowbacktoGTI > TheJWT 03/27/2020 at 16:05

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Probably a good place to start. It the master can’t get the fluid to the lines, the lines can’t get it to the calipers.

Future next gen S2000 owner > TheJWT 03/27/2020 at 16:13

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I’m not sure but I’ll supervise from 6 feet away, drinking my beer while scratching my head.

just-a-scratch > kanadanmajava1 03/27/2020 at 16:14

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If it's stuck, would the plunger also sit there and not rebound? I mean, if the Piston is stuck, the return spring inside the mc would not do anything but sit inside staying compressed.