Disc brake mount overspray / unfaced - causes noisy braking?

[TheMaso]

Hi, I started this thread on a Facebook forum for Giant TCR and have maybe learned a few things from that. So I wanted to ask a more specific question here… I have a brand new 2023 TCR Advanced Pro O (Ultegra 12sp) and the front brake has been noisy since day 1 - after a few trips back to the bike shop where their response was a combination of blaming me for contaminated pads or “not braking properly” (I just upgrade from a 2016 Defy with disc brakes which I rode over 30,000kms without having this issue once) and they eventually replaced the pads and rotors (twice) and even the front wheel. Still no better.

The Facebook forum asked me about brake mountings and overspray. So I checked and Lo and behold there’s a !! BAN ME NOW FOR SWEARING !! ton of paint on one of the mounting holes.

From the photos (bottom mounting good, top mounting bad) does anyone have experience of fixing or having this issue fixed (faced) and did it make the necessary difference?

Good mounting; https://mega.nz/file/KRh2GCYS#yQ5Y-afW_ ... QlOqtC_We4

Bad mounting; https://mega.nz/file/KcBwXCpD#I7HcCU4A4 ... McIovLS0TU

On the bad mounting, the screw is also extremely tight and even feels like it’s cross threading.

I intend to take it back to the LBS this week when I get a chance - and I intend to ask them to also check the rest of the surfaces for overspray as I also have excessive clicking and creaking - much more so than on my old Defy.

Cheers,

Greg

[Duck!]

I've seen it on a few rear mounts, and not only on Giants, but not on forks, although it's entirely possible. If the mount faces aren't perfectly square, the caliper will sit at a wonky angle and cause the brake pads to drag on the rotor; the constant drag induces very high pad surface temperature which causes it to melt and resolidify into a glassy, noisy and very low friction surface. This glazing is often misdiagnosed as contamination, because most of the symptoms are similar. The glazed surface can be sanded off and the pads can work fine afterward, but if the caliper misalignment/mount facing isn't addressed the glazing will be a recurring problem.

A misaligned caliper will also give a really spongy brake feel, as rather than pressing the pads squarely onto the rotor, they will force it to bend into their alignment before doing any proper braking.

If one of the caliper mount bolts is cross-threaded it also won't be evenly applying its force the the caliper mount, which may cause the caliper to sit a bit off, also leading to the above-noted problems

[TheMaso]

Thanks, Duck!

I’ve not had it explained that way but it makes total sense - I can’t say I’ve noticed the brakes being ineffective once they become noisy but each time the shop is replaced the pads (each time saying they were contaminated) they were fine for a ride and then became very noisy again. They seem noisier when “cool” like after they haven’t been used for a while during a ride. If I brake, they make a noise, they warm up and then aren’t noisy until I don’t use them for while (and presumably they cool down again). At least that’s what it feel like.


I’ll take it in tomorrow and hopefully they won’t argue the toss (and hopefully they have a facing tool).

Thanks…

[TheMaso]

Random update that this issue has still not been resolved.

They faced off the overspray (quite aggressively by the looks of things). This didn’t fix things. Then they changed the rotor and the callipers and them swapped back and front callipers then tried a different model of rotor. I’m now running with some Swissstop “silent” brake pads and the noise and “feel” is still there - with the pads it seems like just trying to treat the symptoms and not find the cause.

They have a new fork on order. Just about the last thing to change. Although I suggested the thu axle also.