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New (to me!) '77 CB400F - US model
mattsz:
Thanks! I've read here that sometimes the tiny passage in the master cylinder ("compensating port"?) can get blocked, stopping the piston retracting - I'll look at that, then see about the caliper. It will definitely need attention over the winter, but I'd like to be able to wheel it into my neighbor's basement for winter storage, in the meantime...
SteveD CB500K0:
More common cause of sticking piston is dirt and corrosion.
As long as you own one of these bikes, you will be paranoid about front brake sticking.
I am.
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K2-K6:
As above, it's the caliper usually.
They have no, as in zero, weatherproofing in regards to the seal and overall design so need to be cleaned scrupulously and reassembled to make them work correctly.
They are very simple to work on so don't present a problem in that regard, but may need a new seal plus careful inspection of the piston to assess for corrosion. If the piston is corroded they are generally available and not too costly.
As Bryanj's post, the only way the piston will come out sometimes is to pump it out with the lever while holding in a bucket.
mattsz:
Well, poking at the holes in the bottom of the reservoir didn't accomplish anything - when I pulse the brake lever in and out, I can see a little rush of fluid flow back into the reservoir from one of the holes. The wheel is still stuck, though, so caliper it is.
FYI... new brake master cylinder diaphragm:
Mine:
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Obviously no good, and behind that kink there's a rip anyway. Looks like rebuild kits don't include the diaphragm, either...
mattsz:
Ok, so I thought I'd remove the front wheel so I could squeeze the caliper piston out with the brake lever before dismantling. Let's see, step one: "remove the speedometer set screw." Easy enough. Hmm, the recess looks pretty small, what size allen wrench is that? None of mine fit. Wait, where's my damn glasses, that doesn't look quite right:
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Wha? Quick forum search for that set screw... oh. So this is how it's going to be, huh? (sighs...)
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