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Using a different model brake master cylinder for project?

Discussion in 'Technical and Troubleshooting Torque' started by 79_rd250, Apr 19, 2011.

  1. Hey everyone, I'm doing up a 79 rd250, which due to its age has a few parts that are just too far gone from rust/corrosion/stuck from sitting for a million years. One of the worst bits is the front brake master cylinder assembly. I'm wondering would it be possible to use a different model or brand brake master cylinder assembly on the bike? the problems I can see is the new one being a different size/pressure etc than the old one, which could make the front brake behave weirdly. The other part of me is thinking that if its made for a similar size bike it should be alright or very similar and therefore able to be used. Is my reasoning sound? Am I a downright idiot?

  2. Not sure but are the brakes on the RD250 the same as that used on the RD125?

    If so they were still making those up until very recently, as the "RX-Z" sold in Malaysia and Singapore.
  3. If youre handy with a jigsaw and drill, (or know someone that is) grab a single caliper and master cylinder set off something recent. You just need to make a bracket to adapt the caliper to the fork leg. Depends on how much mucking around youre prepared to do.
    Also check the switch gear will fit..
  4. If you're going to use it with the stock caliper, you need a master cylinder with the same bore diameter. That's the critical bit.

    Bigger bore will give you less lever travel but will require more effort for the same level of braking, possibly giving the impression of squeezing a block of wood. Smaller bore will require less effort but will give you more lever travel, possibly to the extent of the lever reaching the grip before you achieve maximum braking. Poor man's anti-lock :shock:.
  5. What pat said, unless you are after the change. I went to a larger bore on the GSXR in order to get travel back. I had to squeeze a bit harder, but that was fine.

    The good news is that 98% of road bikes fall into 2 different sizes. I can't remember what they were.
  6. Thanks for the replies and help everyone. Amazingly I managed to get everything freed up so pending proper testing it might actually be alright to use.
  7. I hope you've at least put new seals in.
  8. As of today it stopped working again. After pulling it apart I've determined it's beyond repair and I'll either need a replacement or bits off something else.