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Creaking brake calipers
Last Post 12/22/2017 09:48 PM by SideBy Side. 4 Replies.
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6ix

Posts:253

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12/19/2017 02:54 PM
With the bike clamped in the workstand, I get a very pronounced creak/groan from the caliper when grabbing the brake lever hard.  I know the cables and housing need replaced but the creak is coming from near the pads.  Wheel isn't spinning either.  It's like the brake pads bite down and then the dual-pivot part of the calipers kicks in and emits this creaking sound.  You can even see the things flex.

Ideas?  This is Ultegra 6800 (center-mount brake, not direct-mount), Exalith pads and Ksyrium SLR wheels.

I'm perplexed. 
Cosmic Kid

Posts:2438

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12/19/2017 04:22 PM
Did you try dropping a few drops of lube on the pivot points? I've never had the creaking, but have done that in the past for sticky brakes.
Just say "NO!" to WCP!!!!
79pmooney

Posts:1951

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12/21/2017 01:59 PM
Dual pivot brakes are asymmetrical. Both in pivot locations and leverage. I have found if I set up the pads equal distances from the rim, they don't hit the rim at the same time and moreover, as I squeeze harder, they push the rim to one side.

So my conjecture - as the rim is being pushed to one side, the distances from the pivot to the rim change but not the pivot to the pad so the pad has to slip up or down a little or the caliper arm has to bend. (Bend, slip, bend, slip, repeat. Energy lost, in the form of sound with a signature frequency and a few harmonics. Adding up to a "creak".) If my guess is right, you would never hear this with the wheel moving since slip is already happening (and you and the manufacturer have carefully dialed in the toe-in and arm stiffnesses to prevent squeal. Squeal, a prolonged higher frequency creak.)

When I can, I set dual pivot calipers to move the rim as little as possible. Sometimes this means one side has to be too close so I compromise between acceptable clearance and as little movement as I can get. (I have never seen this talked about anywhere, but I have seen it on every dual pivot I've worked on.)

Now, you could get rid of the creak by "toe-ing in" the pads. This would mean rotating them about an axis parallel to the mounting bolt through the fork or frame. I think that one would have to be rotated up so the bottom hit first, the other down so the top hit first (more easily done with canti/Mafac style pads but the dual pivot people haven't gotten there yet).

When the big manufacturers start addressing vertical toe-in so their brakes pass the no squeal test while being squeezed in the bike rack (and they do it by bringing the canti style pads back into style), we will all benefit because with mechanics struggling to adjust the thousands of brakes with those pads. demand for the canti pad alignmnet tool will goi sky high. (That tool we have heard of but that makes 144 BCD 41 tooth chainrings look abundant. It - or a compeitor's version; I'm pretty sure the patent is long expired - will be on the shelves at every bike shop.

Brake creak. Do yours? Want the quietest bike in the rack? You need ....

Ben
6ix

Posts:253

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12/22/2017 02:27 PM
Quite the insightful post, Ben! Interesting. I honestly can't quite figure out how to add toe-in to the pads on these Ultegra brakes but it's working fine now. I get the unique Exalith jet-turbine sound when braking but no squeeling.

I did lube all the pivot points like CK suggested. Combined with brand-new housing and teflon-coated cables, it brakes perfectly again. They are more than powerful enough and don't require an enormous amount of pull on the levers which leaves me asking why bother with disc. Granted, it was dry today but still doesn't seem worth the hassle to me.
SideBySide

Posts:437

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12/22/2017 09:48 PM
Wow, that was a cool description. I learned something. Even though I don't have duals.
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