SOHC.co.uk Forums > CB750

Front Wheel/ Brake binding?

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ColinHH:
Sorry, but you can probably tell that I am doing quite a bit of work on my K4 at the moment and thanks to this group I am gradually getting through it. Electrics done, front fork oil seals done and now looking at the front brake caliper.
My first question is, how freely should the front wheel spin when brake not being applied? With the pads depressed and the back pad adjusted with the swing arm screw, so that it is just off the rotor, the wheel free wheels and will turn 3 or 4 revolutions before it stops. However I then pull the brake lever and obviously the brakes engage and the wheel stops really well, but once I release the brake lever the wheel won’t free wheel and whilst I can turn it the pads are binding. I think this is why it has been so difficult to move it around in the garage. I took the caliper apart and there is some pitting on the piston! I cleaned everything and very lightly used some wire wool to clean around the metal edges of the pads. It still binds. So is this normal or do I need to get a new piston and seal or is there anything else that I should be looking at? Thanks.

Johnwebley:
This is normally caused by the moving pad not retracting,

Can be caused by it being a tight fit in the caliper, or,as well the piston seal is old,gone hard so not pulling the piston back,

Have you replaced the seal?



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florence:
agreed John.  I cannot remember how many times I have rebuilt my front caliper.  Periodically, it starts to stick and the only remedy is to strip, replace seals and often the piston as well.  Currently have a stainless steel piston in and fingers crossed it seems better.  Luckily, it is very easy to rebuild these and the brake bleeds very easily.

ColinHH:
Thanks, new seal and piston just ordered. Another thing worth mentioning is that the “static” pad (The one that is held by the clip on the inside of the disc) is virtually worn down to nothing but the moving pad (the one which gets pushed by the piston) is hardly worn at all!

McCabe-Thiele (Ted):
That might be due to the top pivot being seized as after the brake has been applied the fixed pad needs to be pushed away from the disc by the natural high point as the wheel rotates. Any binding on the pivot action will wear the fixed pad away.

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