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Honda '79 CB750K Master Cylinder Replacement

Discussion in 'Technical and Troubleshooting Torque' started by bigev, Jul 2, 2014.

  1. Evening all,

    I've got an Australian '79 Honda CB750K that I need to rebuild, or replace the master cylinder on. It has two single calipers on the front.

    Looking at the master cylinders on DCC for example, are the 5/8" piston units the correct size for this setup?


  2. Probably best to pull it apart and measure it. That way, if you can't get the rebuild kit, at least you'll know the diameter after market master cylinder you'll need. (y)
  3. The most simple things one sometimes over looks ... Why did I not even think to do that!
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  4. Where in Melb are you? I have a set of internal micrometers that you might find handy. I'm in North Balwyn.

    Oh, and I just remembered that you'll need to measure the lever ratio - approximate will be near enough for this. OTOH, if you decide to upgrade the calipers, you'll need to change the master cylinder diameter to suit.
  5. Cheers. I'm in Fitzroy, I'll wander out to the garage tomorrow after work and measure it all out. I've a pair that will suffice for the moment.

    Measure the lever ratio? It is for the standard calipers. Say the current piston is 5/8" then it will operate just as good, or better, on a 1/2" piston?
  6. On a 1/2" piston and the same brake lever ratio, less force will need to be applied to the lever to get the same braking force, but there will be more lever movement, and it could potentially reach the bar before you get full braking force. It's an engineering balancing act. ;)
  7. Cheers, makes sense. Thanks mate!

    Hopefully get this thing on the road in ready for spring. New shocks, tyres and tuning is hopefully all I now need.
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  8. The 900's had the size cast into the cylinder underneath? Maybe yours does as well?

  9. The piston was 5/8, didn't notice those markings when I reco'd but will look tonight regardless.

    Cheers mate.