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Rim Brakes Grabbing

Old 01-24-21, 04:06 PM
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alecd
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Rim Brakes Grabbing

My Shimano 105 rim brakes grab once per wheel revolution. Particularly noticeable at low speed. I have attempted to true this wheel multiple times. It is within 1mm true (and I can't get it any better), but the brakes still grab.
Any ideas what else I should check? I think the calliper mounting bolt is tight. Brake blocks recently refaced.
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Old 01-24-21, 04:22 PM
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trailangel
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Open up the brake slightly. Adjust the cable
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Old 01-24-21, 04:30 PM
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Front or rear? Can you feel it on the bike or just on the stand? Have you cleaned the rim? Of course if you are feeling a bump where your rim is out of true, you have to true it better or live with the bump. Sorry if that's stating the obvious. I'll just throw out that I solved a persistent rear brake (8000) squeal by adding a serrated washer to the mounting bolt. Seems as if brakes used to come with those but these 8000s only had a flat washer. The front brake is still happy with the flat.
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Old 01-24-21, 05:29 PM
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Two thoughts. 1) get your rims squeaky clean. Good brake pads. (New or freshly sanded.) Patches of sticky liquid can be very grabby. 2) look hard for irregularities in the rim surface. (Mismatches at the joint opposite the valve, flare out from pothole hits, bulges out in the sidewalls at the spokes ...)

One way to find these issues is to ride slowly down a steep hill. (Perhaps marking the tire ahead of time with pieces of tape so you can see (for example) "oh, it's grabbing 5" in front of the red tape"). Rear tire is easier. Just lock up the brake and come to a stop. (Yes, I said slowly!)
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Old 01-24-21, 07:53 PM
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Originally Posted by trailangel
Open up the brake slightly. Adjust the cable
How is this advice supposed to help? The OP says his brakes grab once per revolution...opening the brake will do precisely nothing. It's most likely either the seam or there is some pad residue that's built up at the spot that the brake is grabby and that needs to be cleaned. Please think before providing 'advice' like this.
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Old 01-24-21, 08:14 PM
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Often we forget to check spoke tension when truing our wheels. Your wheel might be coming out of shape when you put weight on it. Just check the ping on each spoke if you don't have a tension meter.

It's especially important with heavy guys like me.

(just another thing to check off on that long list of trying to figure out what's up)
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Old 01-24-21, 10:15 PM
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If the issue is with brakes one should not improperly set them up to "get rid of the problem" all that does is maybe get rid of the noise but doesn't actually solve the problem. Clean everything really well (nothing with oils in it) and end with isopropyl alcohol (or just use the alcohol if nothing is sticking to the rim). Maybe also use something like the SwissStop PolierGummi cleaning block or some light sand paper (be careful not to go too far). Once everything is nice and clean make sure nothing is misaligned on the rim no bits sticking out (seams, dents...) then check your spokes and make sure they are evenly tensioned as well. Also make sure everything is properly toed in and tightened to correct torque specs and the wheel is properly aligned in the dropouts.

I might also recommend checking cables and housing and making sure you aren't having issues due to that either (which is unlikely). If nothing else try a different wheel and see if that solves it.
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Old 01-24-21, 10:55 PM
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One other thing to check is that the pad is not contacting the tire when the brake is applied. Tires often have irregularities which can put the sidewall in a position to rub the brake pad or carrier at a certain point in it's revolution if the pad is positioned too high on the brake track.
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Old 01-25-21, 04:23 AM
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Originally Posted by trailangel
Open up the brake slightly. Adjust the cable
Yes.But first confirm the rim can't be trued any better and it is not rim damage. Look where the rim contacts the brake pad to check.
Open up the brakes a little and check the operation.
Are the brakes still useable. Are you worried if you have to brake?
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Old 01-25-21, 10:42 AM
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Originally Posted by cxwrench
How is this advice supposed to help? The OP says his brakes grab once per revolution...opening the brake will do precisely nothing. It's most likely either the seam or there is some pad residue that's built up at the spot that the brake is grabby and that needs to be cleaned. Please think before providing 'advice' like this.
Mr Pro Wench.... opening the brakes up will keep the brakes from rubbing once per revolution. He didn't say it rubs once per revolution when he applies the brakes.
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Old 01-25-21, 10:57 AM
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Originally Posted by trailangel
Mr Pro Wench.... opening the brakes up will keep the brakes from rubbing once per revolution. He didn't say it rubs once per revolution when he applies the brakes.
You can't be that clueless.
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Old 01-25-21, 12:09 PM
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OK Richard.. I'm Clueless. Clue me in.
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Old 01-25-21, 12:19 PM
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Originally Posted by cxwrench
You can't be that clueless.
Although he should have suggested that the OP make sure the tire isn't hitting the pad, if the rim is really only 1mm out and the OP can't make it better for whatever reason then the obvious solution is, adjust the brakes better. If the pad can touch in one spot at a 1mm out of true spot the pads are too close to the rim. Either the brake has pulled to one side or the OP keeps the pads too close to the rim. The solution in this case is to let out some cable. Not all that clueless.
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Old 01-25-21, 01:16 PM
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If the OP won't have the courtesy to clarify if it's when the brakes are applied or all the time, is it worth arguing over?
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Old 01-25-21, 01:28 PM
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If the rim is hitting the brake pad the problem is with the wheel. You don't adjust the brake and call it fixed, you fix the wheel.
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Old 01-25-21, 02:00 PM
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If the brake pads are adjusted so closely to the rim that a 1 mm wobble means you're rubbing, I don't think the wheel is the problem. At least on all my bikes I have full brake pull with a couple mm (or more) clearance.
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Old 01-25-21, 02:32 PM
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Originally Posted by pdlamb
If the brake pads are adjusted so closely to the rim that a 1 mm wobble means you're rubbing, I don't think the wheel is the problem. At least on all my bikes I have full brake pull with a couple mm (or more) clearance.
Agreed. And since even Shimano recommends for 105 5800 brakes that the pad clearance to rim of both side added together to be between 3 to 4 mm. Split that evenly and the pads should have more than enough clearance for a wheel 1 mm out of true to still miss them.

So it seems to me a reasonable thing to open the pads as trailangel suggested and/or center them better on the wheel. I've had wheels that ran less true than 1 mm and never thought that a problem of the wheel that needed fixing when the brakes opened up wider still braked effectively enough.

Between the 20 dollars to get the wheel trued up better or widen the brakes for free, I'd go with free.

But there isn't any guarantee that this is the OP's issue based on what's been said so far.

The other likely thing is the rim joint being slightly rough, but that usually is an issue when the brake is applied. Which I don't think the OP has stated yes or no on that yet.

Last edited by Iride01; 01-25-21 at 02:38 PM.
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Old 01-25-21, 02:51 PM
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Wow, a lot of replies. So many in fact that I have yet to write down a list of things to check!
This is a front wheel. The pads don't touch the rims when not braking.
When they finally contact the rim (at the same time), they grab at low speed. Once per revolution. Don't notice it so much or at all at medium / high speed.
The wheels (Cero AR30's) did this from new. They have been ridden only last summer. My original wheels don't do this, so it must be to do with the AR30s.
I'll clean the rims with meths (Isoprol Alcholol is hard to get in UK for some reason). I'll mark where the grab is with red tape (on a spoke?). I'll inspect that area for dinks in the brake surface and rim in general. I'll check that the tyres are seated absolutely correctly and no bulges. I'll check that the brake pads are not fitted too high and rubbing the tyre in any way at the point of grab, I'll check spoke tension while truing, check pads are toed in and torqued and I'll probably replace the pads with new ones. And I'll get back to you!
Thanks.
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Old 01-25-21, 03:02 PM
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Sounds as if it could be the seam in the rim. If that's it you can sand it down.
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Old 01-25-21, 03:08 PM
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I've never sanded the rim joints down. All the ones I had that caused the brakes to grab fixed themselves after a very few rides. And none seem to have ever damaged the brake pad.

But I am okay with sanding if that's what someone wants to do.

Last edited by Iride01; 01-25-21 at 03:12 PM.
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Old 01-25-21, 03:24 PM
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Originally Posted by pdlamb
If the brake pads are adjusted so closely to the rim that a 1 mm wobble means you're rubbing, I don't think the wheel is the problem. At least on all my bikes I have full brake pull with a couple mm (or more) clearance.
Jesus, how can the wheel not be the problem? The RIM is hitting the brake pad. If you can't true it to less than that and eliminate the problem the rim/wheel needs to be replaced. I am like you and prefer more pad clearance but not everyone does. 1mm should be no problem.
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Old 01-25-21, 03:29 PM
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Originally Posted by Iride01
I've never sanded the rim joints down. All the ones I had that caused the brakes to grab fixed themselves after a very few rides. And none seem to have ever damaged the brake pad.

But I am okay with sanding if that's what someone wants to do.
Yeah, I've never actually had a bad rim but I read on the internet that sanding is the fix.
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Old 01-25-21, 03:33 PM
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Since this is a front rim brake wheel, flip it and see if the problem persists or changes or....
I'd inspect opposite of the valve stem where the rim joint is. Manf. states it's a welded joint. Maybe it's "rough" or not aligned.
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Old 01-25-21, 03:48 PM
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Originally Posted by Iride01
I've never sanded the rim joints down. All the ones I had that caused the brakes to grab fixed themselves after a very few rides. And none seem to have ever damaged the brake pad.

But I am okay with sanding if that's what someone wants to do.
I use a file. Harder to accidentally create new lows if you file parallel to the brake track. (Haven't done it in decades. The aluminum rims I use now don't need it until I hit something hard (with inadequate tire pressure).
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