Dura Ace C24 wheels - sticky brakes issue

by Zermattjohn   June 24, 2014  

Hi all - I've been experiencing shuddering/throbbing brake issues with this wheelset. I've got Dura Ace brakes too, and the pads are new but I get a real "pulsing" feel when braking. Its pretty disconcerting and sometimes means that the rear locks up it it grabs the rim. It almost feels like the wheel is out of true, or has oil on half the rim, neither of which is the case. I've used Ultegra wheels and the issue doesn't occur, so its got to be something to do with either the rim being faulty, or the brake pads being incompatible. However the rim on both Ultegra and Dura Ace C24 is alu...? Anyone else experienced this issue? I've had a few pairs replaced as the supplier agreed there was a problem, but it keeps happening with each replacement. Pulling my hair out - the wheels are great when you don't want to slow down!

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Few threads on WeightWeenies mention the same thing, but no one seems to be able to solve it.

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posted by glynr36 [278 posts]
24th June 2014 - 10:44

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I did read on there, or somewhere, that using carbon-specific brake pads helps as, even though the rim is alu, due to the carbon laminate there's an amount of carbon on the rim. But, also that these brake pads are very wearing for the rim - these wheels are £600 so am loathe to risk destroying the rim.

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posted by Zermattjohn [60 posts]
24th June 2014 - 10:55

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I have the same problem with Shimano RS80's.Local bike shop trued the wheel and i moved my pads a bit further out.Its better but but still not smooth.
I put a short straight edge along the rim and found one area with a small dish.
Looks like a machining fault on mine that can't be trued out.
Did a wet ride a couple of weeks ago with some steep descents and i was on my nerve ends with the grabbing.

joeegg

posted by joeegg [36 posts]
25th June 2014 - 9:05

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Isn't it amazing how poor new wheels can be? Obviously they churn them off a production line, but to me, more than £400 is enough to spend on something for them to have been at least quality-checked before going out the door.

I don't think its a minor dish/out-of-true issue, as I've been through 4 pairs and each pair has the same issue, sometimes one wheel sometimes both. I'm thinking it must be the brake pads, though you'd think Dura-Ace alu specific pads would work very nicely thank you very much with Dura-Ace alu rims...

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posted by Zermattjohn [60 posts]
25th June 2014 - 11:31

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Interesting thread...I too have C24's on my bike and am currently experiencing the same thing. At first I thought it might be the brake pads so I had them changed...but the pulsing sensation persists. Not terribly annoying, but on down hills I definitely feel it more. Interested in hearing what others think...

regman

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posted by rnarito [24 posts]
25th June 2014 - 12:22

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That's weird, I've got RS80s (same rim) and have never had this. I think I briefly used shimano pads but have been using Swisstop greens for the last few years.

Assuming the wheels are true, have you checked the calipers are pulling evenly on both sides? Are your pads toed in slightly? Are the rims clean? Is your headset tight?

posted by bashthebox [618 posts]
25th June 2014 - 12:26

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Have you taken a close look at the braking surface?

I thought that my Dura-Ace front wheel had gone out of true because it was grabbing under braking. However, when I put the wheel in the stand, it was perfectly true.

Drove me nuts until I checked out the braking surface. The bit that was grabbing was a tiny raised blob a couple of millimetres across in the middle of the brake track: a little irregularity in the surface.

I've never seen this before on a braking surface. It seems like the metal around it has gradually worn as a result of braking, but this little blob hasn't. Presumably that means it's harder than the surrounding metal??

Anyway, I wore down this blob - tiny screwdriver, careful use of glasspaper (don't blame me if it goes wrong) and braking is back to normal.

I only did this a couple of weeks ago. I imagine I'll have to repeat the process in time.

I'd be interested to know if it's the same issue with your wheels.

posted by Mat Brett [1819 posts]
25th June 2014 - 12:36

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I have to say I haven't seen anything obvious on the braking surface. However, as I've been through 4 pairs its pretty odd that the same issue arises on all of them - must be some manufacturing issue? I can't check them at the moment as they've gone back to the supplier (again!)>

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posted by Zermattjohn [60 posts]
25th June 2014 - 13:18

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Braking surface on mine is perfect. Pads are centred.Its the rear wheel only and the slight inward dish is at the joint.The dish is only about 3 cm long so its not a trueing problem.

joeegg

posted by joeegg [36 posts]
25th June 2014 - 17:10

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Highly likely its on the weld/join line - the metal will be more brittle and wear resistant from the heat imparted during the process - as a result the metal wears down faster around it

posted by macrophotofly [24 posts]
26th June 2014 - 10:41

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But its there from the 1st day, so no wearing at all until the 1st brake squeeze. Plus, never felt this on other wheels that must be built in a similar way...

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posted by Zermattjohn [60 posts]
26th June 2014 - 11:13

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Having major problems with my c24 wheels, already had them back to my LBS for a really loud ticking noise under braking, that got sorted, now the rear wheel is screeching under braking, loads of buzzing vibration through the saddle, it's like you say grabbing the rim and feels sticky. I've cleaned the rim and its just getting worse and worse, disgraceful from shimano on wheels that are so expensive.

posted by tonyhogg [60 posts]
26th June 2014 - 17:32

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I have the same problem with RS10's, what is strange though is when I put a different wheel on that does not pulse, there is a significant reduction in breaking. Apart from the actual wheel, everything else is the same, so this leads me to think its something to do with the breaking surface. Heat dissertation could be a cause as the rotating energy is transferred to heat energy, especially as it seems this is a rear wheel problem, but Im struggling to accept that it would be some much that its so noticeable.

For me, the better performance outweighs the pulsing, and its kinda like having ABS on a bike.

Has anyone asked Shimano

posted by jason.timothy.jones [289 posts]
27th June 2014 - 8:40

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ABS on a bike - that's a good way of looking at it. I agree, perhaps the braking surface is almost "too" good, and Dura-Ace brakes/pads themselves are pretty grabby on my Ultegra wheels (which admittedly have a year's more wear on the rim). In terms of heat dispersion, I discount that as it happens the instant I apply the brake, rather than builds through the braking period.

Interesting, though I'd rather it didn't happen.

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posted by Zermattjohn [60 posts]
27th June 2014 - 9:12

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The old 7850 CL C24 wheels used to actually have a caveat in the user instructions that said they didn't recommend the use of their own Dura Ace pads. They are notoriously abrasive, and the thin and fairly delicate rim surface of the CL wheels gets eaten pretty quickly.

I see a fair few wheels with grabby rims, and usually a good going over with a rim rubber and then clean with water sorts them out, especially if they are new.

Swissstop Rim Rubber

I would recommend going to Swissstop Greens on theses rims, they are so much gentler on the surface, and braking performance is generally better.

Complicating matters since 1965

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posted by DaSy [648 posts]
27th June 2014 - 11:36

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DaSy is right. Use SwissStop pads and clean your rims regularly with the rim rubber.

I have 7850s and RS80s and do not suffer from this braking problem either on the steel bike (105 brakes) or the carbon bike (6700 brakes).

However I do suffer from this problem on the front wheel of the fixed bike, which has a 28H IRD Cadence magnesium-alloy rim (Shimano 600 brakes, Kool Stop Salmon pads). This has been extensively investigated and my conclusion is that it's a wind-up effect: the wheel seems to hit a resonant frequency with the steel fork, setting up a shimmy in the longitudinal plane.

The 16/20 spokes in the Shimano wheels under discussion are highly tensioned and if even slightly out of tolerance on the +ve side, this must impart a lateral run-out to one side, then the other.

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posted by harman_mogul [114 posts]
27th June 2014 - 11:59

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