How does the quick-release mechanisim on a dual-pivot caliper brake work?

[Jon George]

Last month, the front brake on my #1 had a problem whereby the quick-release on the brake would not open to allow a clean removal of the wheel. I'm reasonably mechanically minded, but I couldn't establish how it actually worked. Nevertheless, like all good enterprising/idiot Do-It-Yourselfers, I took it to bits and somehow got the brake to work when I finally managed to reassemble it.
I now have an identical problem with the rear brake. As my previous repair was achieved more through luck than judgement, could anyone please tell me the principle and mechanics behind this type of lever so I have a better chance of knowing what I'm doing, this time? Cheers.

 

[andrew_s]

What type of brakes?

Shimano generally have the cable adjuster and the end of the outer fitted on an "over the top" cam with a lever you flip upwards to open the brake.
Campag generally don't have a quick release on the caliper - its on the brake lever instead. This means that if you use campag brakes with most non-campag levers, you've got to let the air out of the tyre to remove the wheel.

 

[Shaun]

Mine are like this - small lever you move up/down to release/tighten:

 

[HLaB]

If it is campy brakes you pull them softly and slide the pin at the lever to the other side, it lets the lever go back slightly more and opens the brakes.

 

[Jon George]

Shimano (I believe 105s). Just to be clear, I know how to operate them, it's just that they've stopped doing what they're supposed to do. If I can find out the mechanical principle - and perhaps a technical drawing of their structure - it might give me more of a fighting chance to rectify whatever is wrong with them.
(I do appreciate I could be missing something devastatingly simple, here. )

 

[Shaun]

Hmmm ... couldn't find a technical drawing of how they operate, only the parts that make up the quick release (if it helps at all?):

 

[Jon George]

Hmmm ... couldn't find a technical drawing of how they operate, only the parts that make up the quick release (if it helps at all?):

I got so miffed at myself for not understanding how such a simple set of components worked, I've just stripped down the rear release lever and realised the screw holding the lever in place had loosened to the extent that the cam element had become disengaged from the key-in section of the screw. Problem now solved - thanks all for your help.

 

[Jon George]

Postscript: Still wasn't completely satisfied, so stripped it down again. I'm now confident I understand how the cam washer is meant to work in relationship to the brake cable, and because of that I've turned it around from the position I found it in. This appears to give me more functionality - with the lever pointing to the axle, the brakes are nearest to the rim, while with the lever pointing to the saddle (not merely at right angles), the cable is relaxed far more and the brakes are open wide. Hurrah!

 

[cyberknight]

holy thread resurrection !
same issue with tiagra calipers that have suddenly stopped opening to let the wheel out , a bit stumped and google isnt helpful

 

[Ajax Bay]

@Jon George - you are not forgotten!
Suspect riders are fitting 28s more these days and on normal (ie 15mm inner rim width) rims, a punctured tyre will drop out between the calipers but an inflated one won't (or has to be forced out).

 

[cyberknight]

@Jon George - you are not forgotten!
Suspect riders are fitting 28s more these days and on normal (ie 15mm inner rim width) rims, a punctured tyre will drop out between the calipers but an inflated one won't (or has to be forced out).

in my case 25s on a 14 rim the cam is moving but the brake do not open at all

 

[cyberknight]

just looked the cam is bent on both front and rear so it doesn't work, doesn't look like you can replace it either