550 front brake

[peterengland]

Just had a new tyre on the front and when I put it back there is now no brake at all, brakes were not touched at all during this procedure so at a loss to explain it and attempting to bleed the system to no avail. Have 'sucked through' the nipple as far as possible but nothing much comes out when sucking the stuff or when bleeding. Any ideas?

[hairygit]

Is the caliper correctly adjusted? If you left the caliper in place while removing/refitting the wheel, chances are the caliper piston has been pushed back into the caliper body by the slightest twist of the wheel when removing or refitting it. If the pump the brakes lever do you get a brake at all?

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[peterengland]

no, still no brake after pumping

[hairygit]

Most odd! How old is the master cylinder? And the fluid that was in it?

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[peterengland]

don't know to either question tbh, but it was perfect before wheel removal!

[hairygit]

Okay. Just a theory here, if removing or replacing the wheel did push the caliper in at all, it would have forced fluid up toward the master cylinder, and if the fluid contained any dirt or debris, it may have blocked a port in the master cylinder. REMOVE THE FUEL TANK BEFORE TRYING THE FOLLOWING! Remove the banjo bolt, hose and washers from the master cylinder, then hold you finger over the hole where the hose was and pull the brake lever slowly, and see if you  can feel pressure against your finger. Wear a glove while doing this, and lay a cloth over over your hand, as it may spray fluid about. If you get pressure there, we will need to look elsewhere for a problem.

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[peterengland]

Can feel some pressure and suction when I put my finger over the hole, but no fluid comes out at all, is the master blocked I wonder?

[hairygit]

If there is fluid in the reservoir and it isn't forcing your finger off the hole you're covering, yes the master cylinder is damaged/blocked/needs rebuilding or replacing. Rebuild kits are easily available, but to be honest it is probably easier/safer to buy a replacement cylinder. D.S.S. does a pattern one that looks identical, and works well, several members on here use them. At £29.99 + vat it is barely more expensive than a genuine rebuild kit. That is the best and quickest option to get you back on the road, especially if you're not confident about stripping and rebuilding your old one. Link to the cylinder.   https://www.davidsilverspares.co.uk/CB550F1-SUPER-SPORT-1976/part_123900/

[peterengland]

cheers for that

[robvangulik]

Before buying a new master, i'd start with checking if both little holes in the bottom of the reservoir are open, if either one is plugged it won't work.

[peterengland]

new master from DS and perfect now. Noticed they have a Honda museum next door but wanted £10 to go in! even all the London museums are free entry.

[hairygit]

Glad that's sorted it for you! The London museums are funded by the public purse, that's why they are free. DSS museum is newly built, and all the bikes in it had to be bought, and it was funded by his business, so he deserves to recoup some of his money! That said, it's still cheaper than the London Transport museum in Covent Garden, and there's just a few old buses and bits of a tube train! 

[SteveD CB500K0]

new master from DS and perfect now. Noticed they have a Honda museum next door but wanted £10 to go in! even all the London museums are free entry.

I blew hot/cold over the museum...

A trip down the 70's memory lane for sure but was disappointed by the 500/4 they have in there.

The coffee's free