I've had an eternal struggle with my current bike over brake contamination. The levers and calipers are Shimano Ultegra R8000, so the latest and (almost) greatest.

I first noticed it when I took it to a repair shop (I no longer use) for a bleed, it came back and the front brake would squeal like crazy and at low speeds had little to no braking force. You can stop from speed but then struggle to come to a halt without using your foot.

At around 2000 miles I tried to replace the brake pads, when I took them out they were black with grime on both sets (front & back), not to mention worn down to the metal. I replaced them with the L04C sintered pads, gave the calipers a good cleaning with a towel (no chemicals) and fitted the new set.

Annoyingly all of my braking issues are back, now I probably should have cleaned the rotors, I simply used some Muc-Off disc brake cleaner on them. I would like to know the best way to clean the rotors, I've inspected the pads and they are looking fairly black now, with plenty of tread left. I'm going to abandon these pads and fit a new set. For the rotors I plan to completely remove them from the wheels (they are center lock fitted) and try and treat them off the bike, what is the best way to fully clean them? They have plenty of wear left in them but you can see these black grooves in them, and plenty of muck on the back that I struggle to get off.

Below are images of the rotors after soaking them in disc brake cleaners, waiting and then wiping them down with a clean, microfiber towel.

Front Wheel Outside Rotor Front Wheel Outside Rotor

Front Wheel Inside Rotor Front Wheel Inside Rotor - note the increased dirt on this side

Looking at ways people clean their disc rotors, I've seen plenty of suggestions that I would need to burn the contaminants off the discs. Would the best approach be to remove them and use a blowtorch, should I soak them in some nasty chemicals overnight before I try to heat them? Do I try baking them in the oven?

And finally, what is the best way to prevent the brakes from becoming contaminated in the future? it's really off putting when they squeal and don't perform how I'd expect because it means I'm more reserved whilst out riding on the bike, leading to reduced time riding around outside. I commute on this bike (50 miles a week) and then ride about 50 on the weekends also, so it see's it's fair share of road use. I tend to wash it once after my big ride on Saturdays and will rinse it off if it's been raining, any day that occurs (since I live in north east England, the acid rain..). I've owned disc brake bikes before and never had half the issues I've had with this, I had a cheap Trek with Tektro brakes and the brakes were sharper and never had any issues with contamination whatsoever (I did around 500 miles on that bike before a motorist happened).

Thanks for any and all advice :)

  • 1
    I've seen recommending burning of the pads (though I recommend replacing), but not the rotors. With rotors you could easily temper the steel. Commented Apr 11, 2020 at 14:26
  • Really there are three questions to address. Cleaning, Squeal and stopping power, they may be related, but maybe not. Hard to tell from photos, but that Brake rotor could be damaged. Is it the braking surface smooth with no lips or ridges?
    – mattnz
    Commented Apr 11, 2020 at 20:22
  • 1
    Shimano, Sram and many others advise against the use of automotive brake cleaners. You can use a bike brand specific brake cleaner, or plain rubbing alcohol. As it is a flammable liquid you want to use it in a well ventilated area. I would clean the rotors install fresh pads and break in (also called bedding in) the pads
    – mikes
    Commented Apr 11, 2020 at 22:12

2 Answers 2


Isopropyl alcohol and/or brake cleaner from the car trade. Avoid washing up liquid in the cleaning water as it may leave a film of water dispersant. Don't forget the pads or replace the pads if they're too badly contaminated. Heating is a bad idea, it could damage the discs irreversibly.

To avoid contamination cover the rear disc when lubricating the chain and wipe off the excess of lubricant before the ride. Another source for contamination may be slightly leaking seals in the brake callipers.

But then concerning the lack of stopping power after new parts were fitted, did you break-in the pads and the rotors properly?

  • 1
    So when I replaced the pads the first time I did do a ride to bed the pads in. I did 10x hard stops from 15mph and then 10x stops from 20 mph. The brakes felt fine for the best part of 2 weeks. When I refer to stopping power, its about coming to an absolute stop, if you fully grab the lever the disc will squeal horrendously, the noise is so loud everyone on the street turns and looks. It then very pathetically slows down, on the front brake fully squeezed I can actually overpower the brake with one leg.
    – Axemasta
    Commented Apr 12, 2020 at 13:40

It looks and sounds as if your calliper is leaking oil. The most likely cause is the LBS that did not bleed the brakes correctly (eg. by not using a bleed block) and caused the pistons to pop out of their seals. No amount of cleaning will help as oil will continue dripping onto any freshly cleaned or newly installed pads/rotors.

There is only one solution: replacing the callipers, the pads (and probably the rotors as well; they seem to have been affected by the oil). Oh yeah, switch repair shops as well 😉

  • This was peak pandemic and the shop I got it from (evans) wouldn't service it. It did transpire that I had faulty brakes all around, the reservoir on left shifter broke and both calipers were leaking. I argued with them and managed to get evans to send me new parts instead of having them "fix it" themselves. I took those new parts and installed them myself, thousands of miles later I've not had any issues. I deep cleaned the rotors before changing to the new components and the bike hasn't skipped a beat since!
    – Axemasta
    Commented Jun 19 at 15:29

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