Centre pull brake calipers sticking

[Zippy]

These are on a Specialised Hard Rock MTB. Centre pull brake system where the brake cable runs through a rigid sleeve on the centre pull arch.

Problem is the caliper which the cable clamps into is not returning under tension, can be freed by hand but goes with a clunk like soething is holding the caliper back or the calipe has been pulled into the rim too tightly.

I have removed and greased (lithium) both calipers, return springs are on maximum tension, new cable oiled into brake sleeve at handlebar end.

Cable and calipers seem to pull in smoothly, but this one caliper does not return unless I pull it out by hand.

Brake blocks are slightly worn and I have tried adjusting these to be nearer the rims so the calipers have less to travel, but this does not help.

Ideas please before I run the embarrsment of one of those events where they fix your bike for free while encouraging folks to cycle more? (That's next Sunday - can't wait 'til then!).

 

[Jonathan M]

Do you mean the bike has canti brakes?


Has a lip developed on the brake blocks? This can mean when the brake is applied the lip tracks the block close to the rim, if there is alip get a sharp blade and carefully remove it so the braking surface of the block is flat.

Other thing to do is to remove the canti from the boss, and check that the spring has not become dislodged, the coil type spring has an end that is supposed to fit in one of three holes on the canti boss. Usually the hole on the boss closest to the frame will give the spring greater tension, and this will mean the canti arm is more likely to return promptly. Other thing to do while the canti is off is to clean the boss, if rusty use some fine wet & dry to smooth itoff, aplly a litle grease before refitting the canti arm.

 

[Zippy]

Has a lip developed on the brake blocks?

You're not related to Derran Brown are you? As soon as I came off here, I looked at the blocks and found exactly that!

While I'm on though - is there a "how to" guide anywhere that can help me with those 3-dimensional brake block adjusters. You can adjust up and down, toein and toe out, more or less brake block stem and so on. Too many variables! Is there a foolproof guide to how exactly these should be adjusted?

Problem sorted for now. Thanks.

 

[Jonathan M]

You're not related to Derran Brown are you? As soon as I came off here, I looked at the blocks and found exactly that!

I'm pleased to say not, any rim brake that doesn't return properly needs the blocks checking first.

As far as a set up guide, I just bought a maintenance book when I got into MTB'ing years ago, and skills just increased from then.

 

[bonj2]

if a lip develops it sounds like the block is too low.

 

[Zippy]

if a lip develops it sounds like the block is too low.

Thanks bonj. I find that blocks can work themselves lower over time as you apply the brakes with any force. They can work themselves down the rim and form a lip if I don't look to adjust regularly.