Technical > Wheels, Tyres and Brakes
CSS rim squealing
Matt2matt2002:
Using pink salmon blocks.
Over half tread on blocks left
Toe'd in.
Rim dirty with pink 'dust'.
Cleaned x2 with break disc spray cleaner. Pink smears still left on rim
Very loud squealing.
All break parts cleaned and adjusted.
Stops very well and no drag due to pads touching rims.
But the squealing is driving me nuts
Only good point is that I no longer have to ding my bell as a warning!
Rear pads on CSS rim are blue and no issues.
Any experience of a pink squealing?
Rims are 10+ years old and 15,000+ miles. Don't appear concaved yet
Another good clean? With what?
A bike mechanic said that in cold weather the blocks can harden, so trim them with a sharp blade. Not sure I like the sound of that. Maybe roughen them up with sandpaper?
Photos taken after a short ride following the rim cleaning.
Danneaux:
I have answered similar questions from other parties off-Forum in the past, so this is not an isolated case and I will reproduce my answer here in case it helps others...
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Prior thread with Andy Blance's advice recounted...
http://thorncyclesforum.co.uk/index.php?topic=9845.0
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I wrote...
--- Quote ---It may not be the rim, but the brakes. IF XT/R, they have a tendency to develop slop in the linkage that leads to eventual squeal in some cases regardless of rim sidewall treatment. Similar experiences and things tried listed here...
https://www.mtbr.com/threads/xtr-v-brakes-squealing-help.303964/
https://www.mtbr.com/threads/xt-v-brake-squeel-problem.99018/
https://www.mtbr.com/threads/xtr-v-brake-squeal.216381/
The purpose of the linkage was to keep the pads parallel to the rim rather than swinging in an arc with the arm; this extended pad life and was useful when wide tires were mounted to narrow rims, to prevent the pads from striking the tire sidewalls near the rim.
At one time, Shimano made a rebuild kit available, part no. BR-M951/BR-M950/XTR. This included new spacing washers and pad mount/linkage arm/keyed mount assemblies. Cost was about USD$35. No longer easily available but some German firms still carry them, one at a cost of EUR 24.95:
https://www-onlinefahrradshop-de.translate.goog/xtcommerce/304SP2.1_package_full/304SP2.1_release/xtcommerce/product_info.php/info/p882_XTR-Rebuild-Kit-BR-M951---BR-M950.html?_x_tr_sl=de&_x_tr_tl=en&_x_tr_hl=en&_x_tr_pto=sc
I would try swapping the front and rear brakes and then realign the pads to their new locations and see if that quietens things. Alternatively, I'd try fitting a new v-brake without linkage to the front to see if that helped reduce or eliminate the noise. Typically, brake squeal is harmonic resonance caused by the rear of the pad cyclically digging into the rim, then releasing. Besides toeing-in the pads, making sure they are tight in their holders and the holders tight in the brakes can help. Flexible forks can exacerbate the problem, not the case here.
I would also check to see how the spherical washers are set and matched on each side of the mounting brackets and to see if they are spaced the same and mirror-imaged side-to-side. Shimano have detailed instructions at Figure 2 in the brakes manual here: https://si.shimano.com/pdfs/si/SI-B660A-000-00-ENG.pdf
--- End quote ---
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Performing some combination of the above seemed to permanently reduce or eliminate squeal for the other parties, so perhaps it would help here as well.
As for the pinkish dust, I think that is the softer Kool-Stop pad material collecting in the rougher surface of the CSS rim which may not yet be polished enough to prevent grinding the softer pads to dust.
Best,
Dan.
mickeg:
The reason that the extra hard pads were specified for CSS rims was that softer pads could abrade too fast and some of that pad material could become imbedded on the rims.
I would try a harder pad than the Salmon pads.
I am running the Koolstop pads that SJS sold for CSS rims. They are quite worn, but I am on the original pads. But soon, my rears will have to be replaced, I have one pair of CSS pads left.
I occasionally have squealing brakes on my CSS rims, but that usually is in damp weather, not sure why but the squealing is much less prevalent in dry weather.
If I brake harder, the squeal is muted, so I am inclined to alternate hard braking with no braking.
Matt2matt2002:
Many thanks folks.
I now have a weekend project.😉
PH:
I use Salmon pads on my CSS rims, as do two others I ride with, none of us get that pink dust. I suspect Dan is correct and that the rims haven't worn smooth enough for them yet.
I get some squealing from time to time, most likely when there's a dampness in the air, but not often when it proper wet. It doesen't happen often enough for me to be too bothered about it.
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