FZRSupport: the FZROnline Archive

Ok, so I have a thread on my rebuils, and it's going nicely but I thought I'd separate this issue.

Backstory: when I started the rebuild I knew the front master cylinder was toast. It was leaking out of the piston, and wouldn't hold pressure for more than the time you pumped it and held it. But, it would build pressure. So I replaced it. I ordered a factory master cylinder through mrcycles and the piston blew out. Returned it and got a new one. Now, it still won't build pressure. It will push fluid to the bleed ports, I have new clear fluid coming out. So here is what I've done and or tried
1. Zip tied the handle compressed to try and let some air bubble out over a week, moving the bars to change angle the air could collect and move
2. Pump, and pumped and pumped and pumped some more
3. Pump, bleed, pump,bleed etc. Lather rinse, repeat, Yanno?
4. Changed copper washers

Nothing has helped. In concerned that I'm going to blow out the piston again. I'm very mechanically inclined and have done brakes dozens of times. But this one is getting me. Where the Heck do you go from here?

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Have you pulled the piston and inspected the bore? Any pitting, grooving, etc will do bad things to the cup and the back seal.

No I haven't done that. In assuming you are referring to the piston the lever pushes in on. Its a brand new cylinder from Yamaha. Idk why it would be scored or pitted already.

Something I forgot to add, I did fill the cylinder that provides compression with fluid before attaching the banjo bolt. It had a slight amount of pressure, but when bleeding commensed, that went away and never came back. Wanted to make sure the cylinder was lubricated before I started pumping away.

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Sorry - I misread that you had gotten a MC kit.

Did you soak the cup and seal(s?) in clean fresh fluid before assembling it?

Briefly, ten or fifteen minutes maybe. Its got me pretty baffled. I don't know what the deal is. I've replaced these cylinders on bikes before and never had this much problem. I could pump for days and get nothing. Thinking of loosening the banjo bolt and seeing if any fluid comes out at all. The part that kills me. Is if I pull the lever, and crack open either bleeder screw, it pushes fluid put, about half an inch tall, and slows like I would expect, close bleeder, and pump. Crack again and it shoots out the same. But won't build pressure.

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There must be a high point in the system that has air in it. Maybe at the banjo or a splitter further down in the calliper Personally I would start nearest the reservoir ensure fluid is maintained to avoid more air and break each joint top to bottom ensure you have fluid, let gravity not pressure show you the fluid. Once done I'd try to bleed normally, easy bleed if you have one. If not put a 3mm slice following the line of the hose in a piece of 5mm rubber hose and a bolt in the end, fluid/air will come out under pressure and it will seal as soon as pressure is released. If it still won't bleed drain or clamp hoses remove nipples check holes, check threads and use pet jelly on the threads as air goes right back into the system when there is no seal. If that doesn't help take the callipers off their mount and invert and try to bleed, you need an equivalent disk thick ness in between the pads. You can't rule out faulty new components but I reckon it's air that needs shifting somewhere in there, the air going in via the nipple threads is often the trouble. Warning, brake fluid is a paint killer, especially if your paint is aftermarket, soapy water spray is good to have handy, and rags. You just need the confidence in your own words, fluid is coming out the nipples as you apply force so it has to be air, good luck


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This is the second yamaha cylinder I received. I see no leaks anywhere at all from the calipers. I did clean the bleed ports out, one was a bit corroded but I cleared the passage and am getting fluid out of both of them. I'm gonna fiddle with it tomorrow and see where I and up.

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Well I got quite a bit of air out of the system after bleeding again, but I also let it gravity bleed before that so it may have been from that. Still no pressure after pumping for an hour. Still pushed fluid just fine. But no pressure. Im gonna take the calipers off and see if there is something leaking.

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6 out of 8 pistons in the two front calipers were froze shut. Don't know why it qouodnt build pressure but that's what I found. Took it aprt, cleaned it and reinstalled. I'll be bleeding again next weekend to see if it fixed anything.

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Alright. So like I said, I took it apart, and cleaned everything out. There was a bunch of gunk in there so I made sure to clean out all of the stuff with clean brake fluid. Checked all the seals inside for each piston and for the fluid transfer holes, and everything looks great. Put it all back together and leaks checked everything with 75 psi of shop air, and it's all good like the service manual said to. The pistols moved like they should and evrything. I bled it out a bit and I got plenty of air as expected. I just don't think I got it all out. Time and kids restricted me.

Does this all sound like I'm on the right track here?

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Well, I ended up buying a full front brake system off eBay. Its used, but it got here today and it's a complete system and the calipers work as advertised. Not bad for 60 bucks.

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