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Old 10-30-12, 10:46 PM   #1
drbenjamin
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disc brake / pad placement

All

It's started raining out here so I've swapped over to disc brakes up front. I noticed after an especially muddy ride that there is a ~2mm "unswept" dirty area on the outer edge of the disc; the pads appear not to be clamping all the way to the outer edge of the disc. Is this a problem? I was thinking that I would end up with a ridge out there, but then I suppose I'll end up with a ridge on the inner edge of the pads no matter what so maybe it's nothing to worry about. The only way I could see to change this would be to install some spacers between the fork mount and the caliper.

TIA, I can post a pic if that would help
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Old 10-30-12, 11:43 PM   #2
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Originally Posted by drbenjamin View Post
...I can post a pic if that would help
It would help to know the model of brake caliper, rotor, and pad (aftermarket, OE). Without knowing those details, the first thing that comes to mind is the pads are not clipped in all the way.
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Old 10-31-12, 01:07 AM   #3
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Is this just a pad replacement on the same, otherwise, un changed [mystery] caliper?

Perhaps you need on site help,realistically, not online guessing from a couple phone pictures..

bike shop service people where you live, can see better..

Last edited by fietsbob; 10-31-12 at 01:13 AM.
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Old 10-31-12, 01:40 AM   #4
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Originally Posted by drbenjamin View Post
It's started raining out here so I've swapped over to disc brakes up front. I noticed after an especially muddy ride that there is a ~2mm "unswept" dirty area on the outer edge of the disc; the pads appear not to be clamping all the way to the outer edge of the disc. Is this a problem?
What exactly are you describing here? Does the footprint of your brake pads actually cover the outer edge of the disc (and yet it remains unswept)? Or do your pads entirely miss that peripheral area?

It is probably the latter, i.e. the pads don't even cover the most peripheral "ring" of the disc. This is actually perfectly normal. For example, this is exactly the way it is in a typical BB7 setup. About 1-2 mm next to the edge of the disc remains unswept by the pads.

Just make sure that the entire pad footprint falls into the "braking" area of the disc. As long as it is the case, it won't make much difference where exactly that footprint rides, closer to the center or farther from it.
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Old 10-31-12, 07:52 AM   #5
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The best match is with rotors and calipers from the same company. If you've got that - no issues.

Otherwise some combinations just don't work well . Worst case scenerio came onto the shop last month and was the opposite of what you've described. The swept area and pads actually extended 2 mm PAST the rotor edge. As the pads wore that outer 2mm didn't get used and eventually the unworn lips met each other and .... no brakes!

If you have any serious reservation just drop by a decent shop for a second opinion. Brakes can save your life - but only if they work when you need them to.
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Old 10-31-12, 06:50 PM   #6
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Thanks all and sorry for the lack of detail in my first post. My setup is a ENVE 2.0 road fork modified by calfee to have disc brake tabs. I use rim brakes in the summer then mount a road BB7 caliper in the winter, stock 160mm rotor. I used this setup last year, then overhauled the caliper this summer. The pads are the originals and are 3.2mm wide so I didn't replace them, just remounted them.

When I say "unswept" I mean that most of the braking surface of the rotor is shiny but the outer 1-2mm is dirty, it looks like the pads are not reaching that far out but it's hard to confirm as there's not much visibility near the top of the pads.
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Originally Posted by AndreyT View Post
It is probably the latter, i.e. the pads don't even cover the most peripheral "ring" of the disc. This is actually perfectly normal. For example, this is exactly the way it is in a typical BB7 setup. About 1-2 mm next to the edge of the disc remains unswept by the pads.

Just make sure that the entire pad footprint falls into the "braking" area of the disc. As long as it is the case, it won't make much difference where exactly that footprint rides, closer to the center or farther from it.
So it sounds like the appearance of my rotor is normal and nothing to worry about. I will double check that the innermost surface of the pads is not extending past the braking area of the disc.

Thanks for the help! I've learned a ton from this forum and am always grateful for the advice people give.

Last edited by drbenjamin; 10-31-12 at 07:21 PM.
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