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Any ideas what could be wrong…
Bike 1 scribe centrelock wheels. Force disc brakes. Ultegra discs squeal and howl. XT discs squeal and howl. SRAM discs total silence. All with no adjustment to the calipers.
Bike 2 scribe centrelock wheels. Ultegra brakes. Ultegra discs squeal and howl. Xt discs squeal and howl. Not tried sram yet but superstar basics 6 bolt on superstar wheel = almost silent.
In both cases the disc is central and as true as can be. Neither brake is leaking at the caliper (
Tissue test overnight.)
The shimano roto fins do seem pretty flimsy and like they’ll vibrate at the drop of a hat and I know theres a host of reasons for squealing brakes but the fact i can go from howl to silence just by swapping discs seems to indicate its a shimano rotor issue. Or am i missing something?
If the discs are contaminated, they don’t always recover well or easily. The last time after a Shimano micro leak they needed oven baked at 170deg and then IPA while they were still hot and then lightly sanded. This could be why the problem travels with the discs.
Another option could be that the discs have reached their minimum thickness. Normally this wouldn’t matter much, but on those rotors it might affect stiffness, which would in turn affect frequency.
pads - wash disc with washing up liquid then sand. Put new pads in
I can get this if wheels have been sitting in the garage for a while (even if not fitted to a bike). I use rotor cleaner and might even bake the pads for a while. Never fails.
To be honest, that fits. bike 2 been standing for the summer. And both sets of shimano rotors have been on wheels not used for a while.
I’ll try a bit of sanding, cleaning then re bed in. Need a night when she’s out before i can try baking!
I do this for a living - it’s just the different disc designs and their weight.
It’s all about the ‘free-resonant-frequency’ of the disc, wheel, pads and caliper.
If they align favourably = silence.
If they don’t align favourably = howling.