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Brake master cylinder rebuild

Discussion in 'Technical and Troubleshooting Torque' started by Fitty, Mar 30, 2010.

  1. Is it worth repairing a brake master cylinder, or should I just get a new one? The boot around the piston is perished and will need to be replaced, but the diaphragm is fine, and so are all the other internals. If it is worth repairing, do manufacturers supply rebuild kits or something similar?

  2. You can buy a genuine rebuild kit for somewhere around $60 or less, I'd expect. They come with all the seals, plus a new piston and spring. You'd be well advised to hone the cylinder too.

    Or... Head down to Vic Wreckers and get yourself a f*ck-off giant radial master cylinder off some late-model sportsbike. I got one for well under $200, and they're the business. You'll stop like somebody just hit the pause button. :)
  3. Yeah, sounds like a good idea. I think I'll have to take some time to get down to the wreckers by the end of this build. I can't see a reason why you couldn't just swap out the bmc, but to be on the safe side, do you need to swap the whole system?
  4. I've just put a ZX10R master cylinder on a ZX9 and it feels lovely. You can't switch the calipers over too, because your disc sizes, mounting points and everything are all going to be different.

    The only thing you have to worry about is making sure you're not getting something that pumps out a vastly different pressure at the m/c. Having said that, the Vic Wreckers guys all race 250cc 4-strokes, and they've all got superbike radial master cylinders on their little 250s, so I'd imagine you'll be fine. Ask them about it.
  5. I wasn't talking about the calipers, just the hoses and the cooler. All good though, I'll have a chat with them. On another topic, I didn't think there was a 250cc class running in Victoria?
  6. ...cooler?

    The hoses will bolt straight on, a banjo bolt's a banjo bolt. You might have to bend a bit of aluminium to mount the reservoir. Nothing too serious. Handlebars are all more or less the same diameter so the clamp will be fine too.

    Yeah 250 4-strokes race in... I forget what the class is called, but they often put them in the same races as the 650 twin sprints and 400s. They race in interclub and also the Vic championships. Not sure about the Aussies - but they reckon it's the cheapest way to go racing. You can get a bike up for less than 2 grand. :)
  7. So finally after all that rooting around do they work Loz?
  8. **** oath they do Kenny. Will wait to see if they hold pressure before having the stoppie party though. And they need HH pads before they'll feel right to me.

    In other news, as soon as I fixed the brakes, I realised the shock was munted. Here we go again. :)
  9. Yeah, the bike I'm playing with has a heatsink sort of thing bolted to the front of the left fork leg.
    I was looking for something like that a while back. I'll look in to it.
  10. Mastercylinder replacement idea is good, works a treat on twin disc bikes, but be aware that you have only 1 caliper with 2 pistons, when most of the newer radial mastercylinders are operating 2 calipers with 4 or 6 pistons each - a total of 8 or 12 pistons. It might be a little abrubt.....

    Dont think the heat sink thing is anything to do with your brakes, might be a
    regulator/rectifier? Funny place to put it though....

    Edit! I've just had a look at the workshop manaul for your bike and the only things that should be there are the brackets to hold the speedo cable, brake line, and the horn.

  11. I'm not working on my bike, just a project I'm doing a bit on every now and then (details in this thread). The heat sink is obviously something to do with my brakes because it was full of brake fluid when I took it off the forks, and it's connected to the master cylinder and the caliper. It might just function as a secondary resevoir - the Haynes manual doesn't mention it.
  12. Sorry, I thought you were working on a VTR250, the thing on the bottom of the fork leg looks like an anti-dive mechanism.