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Rear Disk Brake troubleshooting

Discussion in 'Technical and Troubleshooting Torque' started by TallRider, Apr 19, 2010.

  1. Hello,

    Bike: Hyosung Gt250r 06

    I have a problem with the rear brake. It originally was working fine, though there was prehaps an inch of depressing the lever before it started to brake. Then one day after riding for 45 minutes, the brake got stuck on after stopping at the lights, just near home luckly as it got progressively worse everytime I used it. When I came back the next morning the brake had released and I could push it in neutral fine.

    Now there was only about a cm at the end of the levers motion where the brake would engage. So about 2-3 inches of lever travel. I attempted to bleed the brakes and on the first press of the lever about an inch of fluid came out, then no more would come out. Got help from someone that has bleed brakes before and this time didn't get anything using a one way valve and pumping like mad.

    Now the brake doesn't work at all.

    No leaking fluid that we could see.

    Question: Has anyone experienced a similar problem and is it likely the master cylinder?

    Just thought I'd check before I spend the money on the part.
  2. it could very well be, I assume you've checked the pads, and cleaned the assembly as well. I've only ever had master cylinders (in cars) fail in the way that you get an initial bite of brake, then it fades to nothing, meaning you need to pump it to get it to work.

    I'd pull the system apart and ensure everything is clean, and there is no gunk blocking the brake line, you could do this by removing the brake lines and either looking through them or using a funnel pouring a small amount of brake fluid into the top and see if it comes out.

    It could be also that you have air in it.

    Be sure the cheap stuff is okay, before you go the expensive stuff.
  3. master cylinder is in need of a kit or replacement.

    could be the caliper, but it is more likely the master cylinder.
  4. Thanks for the advise. I'll take the system apart and have a look, haven't checked the hose. Only new to the mechanical side of things, with this bike being the only thing I've worked on.

    If there was air in the system wouldn't bleeding remove it?
  5. To finish this thread, it was the master cylinder, once I had the new one it was very obvious. As the new one had resistance when compressed whereas the old one just moved about loosely.

    Less than $100 for part plus brake fluid. Due to the cheap pricing of HyosungSource.