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Rubbing disc brakes

Hi,

I have 2014 Cannondale Synapse Disc 105 and I have forever experienced rubbing on the disc brakes, front and back. It is fine most of the time, but after a steep descent with heavy braking, the discs will rub (not for a complete cycle of the wheel) for 30-40 seconds and then gradually settle. I suspect this may be because the disc heats up and warps a bit, then trues itself when it cools. Similarly when riding hard up hill with lots of side to side swing of the bike, the front disc in particular can rub. Maybe the front wheel is not stiff enough? Should I tighten the spikes?

I have tried recentering the discs multiple times. I have changed the discs to new ones. I have dismantled the brakes and reassembled them, changed the pads and even bled and refilled the hydraulic lines, but it still happens.

Has anyone had a similar experience? Does anyone have any ideas to cause and/or solution?

Thanks

Posts

  • wongataawongataa Posts: 906
    Similarly when riding hard up hill with lots of side to side swing of the bike, the front disc in particular can rub. Maybe the front wheel is not stiff enough? Should I tighten the spikes?

    This is not due to wheel flex. The disc is firmly attached to the hub and that won't be flexing. It will be down to your forks flexing slightly making the caliper move slightly relative to the disc.
  • photonic69photonic69 Posts: 1,077
    Rubbing after braking on descents? Yes, some do. Some don't. Mine do. You can minimise it by making sure the area around the pistons in the caliper and the sides of the piston are clean.

    I do this: Take brake pads out. Pump brake levers a little bit to slightly push piston out. Get an old toothbrush and cut the bristles down to about a 1/3 high. Use some cleaning agent such as Screwfix Degreaser (cheap at £9 for 5 litres and you dilute it lots) and scrub the pistons and caliper well. Rinse and repeat. Rinse. I then spray the caliper and piston liberally with GT85 or WD40 and then remove it with a clean soft cloth. You don't want to contaminate your pads. When clean push pistons back in with a tyre lever (Park Tools blue ones work very well for this) . Then look very closely at which piston moves most when you gently pull on the brake lever. One side moves more than the other. Hold back the one that moves most using the tyre lever and work the stiff one in and out numerous times. It will free up.
    Put it all back together and pump brake lever a good 20-30 times to settle the pads. Take for a gentle road test.

    This works for me and my BR-RS505 brakes. It might not work for you
  • RedClipRedClip Posts: 89
    I didn't have the problem with 105 7000 series rotors, but since I swapped them to the Ultegra Ice Tech rotors. Now it's all the time, after a descent. Plus a "buzzing" sound if braking at speed.
    When I get home and check for alignment, they're centred.

    Thanks for the info Photonic69 :)
  • Also, after following the above advice from photonic69, having pressed the pistons back, put a thin piece of card ( or an actual metal brake rotor shim) over the brake rotor, and pop the wheel back into position. Then do the brake lever multiple squeeze thing, release the brake lever and slide the card / shim out.
  • Many thanks for tour comments. I’ll have a go
  • pilot_petepilot_pete Posts: 1,979
    1. Make sure the caliper pistons are moving freely, especially returning after releasing the brake. Take the pads out, pull the brake lever gently to push them out a fraction and clean with isopropyl alcohol on cotton buds.

    2. With the pads back in, ensure the rotor(s) are dead true - use a specific tool or an adjustable spanner to tweak them to ensure they run true - no buckles.

    3. Make sure the caliper(s) are aligned correctly (centred) with an even gap either side of the disc rotor. Adjust if necessary.

    4. If all that doesn’t solve the problem, the chances are there is a tiny bit of air in the caliper - under braking the heat generated is transferred to the caliper and thus to the fluid. The air will naturally expand under heating. This causes the disc pads to remain ‘out’ slightly, contacting the rotor and causing your noise until the fluid/ air cools after the brakes are released. The air contracts and the pads then retract fully to the off position and the noise stops. The cure is to bleed the brakes again. Follow the correct procedure to remove any trapped air in the caliper. This should sort the issue.

    PP
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