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Front calliper sticking

Discussion in 'Technical and Troubleshooting Torque' started by tbbm, Nov 6, 2011.

  1. I've got a CB250 that had a drop and the front brake lever took the impact. Master cylinder was leaking fluid so it was replaced and have bled the brakes but the front callipers are still not releasing fully.

    Replacing the master cylinder has made it seize much less but if I give the front calliper a tap with a spanner, the wheel spins freely until I apply the brake again and, when released, it is slightly seized again.

    Does this sound like the front callipers need to be cleaned or is there some other problem I could be missing? The master cylinder is new and the pressure feels good, the brake engages right and hard and disengage slightly, just not all the way (until the callipers are given a good tap).
  2. Is it a mechanical sticking of the brake lever or a binding of the linkage to the master cylinder?
    I suppose the question is does the brake lever return to the off position when you release?
    Does tapping the linkage to the master cylinder get the brakes to release?
  3. To be honest it sounds almost unrelated to the drop. 99% of the time when I've seen this, it is a caliper problem. When replacing the master cylinder I would have replaced the caliper seals, cheap and doesn't take long. I've had this happen a couple of times when flushing brake fluid, previously working pistons start to stick. I just replace the seals and all is good (usually).

    That is why these days if I'm working on anything where I either don't know the age or I know the seals are over 2 years old I simply replace them.

    It also means you keep the calipers/pistons in good nick which makes it less likely for dirt or anything else to build up and cause problems.
  4. Is it a 2 piston sliding caliper, or a 4 piston? I'd suspect it is the twin sliding given the model of your steed. To fix it, simply remove the caliper, pop the pads out and slide the 2 halves apart. Clean the slide pins and their respective bushes with brake cleaner. For good measure replace the dust boots. Then simply apply some high temp grease to the slide pins, slip the 2 halves back together and check they slide in and out freely. This should solve your problem. About 90% chance of it anyway. If it doesn't, double, triple & quadruple check you have the correct lever for the master cylinder. Then the only thing left to do is replace the piston seals. Pretty straight forward to do. Dig the seals out with a blunt scriber or small screwdriver, clean the caliper bores with some rag and brake cleaner, inspect the pistons for rust & gunge build up. You may have to polish them with some fine wet and dry. Lube the new seals with brake fluid or brake grease, assemble, bleed and test. That will certainly solve your issues. Cheers.
  5. Thanks for the help.

    No, the master cylinder or lever isn't sticking, it feels just right - it's just the callipers. And it's definitely the right lever because it came from a stock bike attached to the master cylinder assembly.

    It's a 2 piston calliper so it looks like a good cleaning is in order. It kinda suits to do it because I've never done it before but looking at some instructions it looks easy enough.

    And I'll definitely get it to the shop after doing it so someone can give my work a once over since the brakes are there to save my life - not doing this to save money, just to get experience. Appreciate the tips!