Why do my disc brakes keep becoming contaminated?

[Tim1023]

Since I've had the bike, I've repeatedly had problems with screaming brakes. I've come to the conclusion that it's simply contamination. On the rear brake, I put this down to careless washing on my part transferring crap from the drive train. Both front and back brakes have similar problems.

However, even when I clean all brake components to within an inch of their lives (including replacing the pads, rubbing down the discs and bedding in), the problem only stays away for a few days before I need to do a deep clean again.

Cleaning regime for pads:
- Clean with brake cleaner, sand down, clean again
- Sometimes additionally: dowse with brake cleaner, set alight, let it burn for about 20s, clean again (once they've cooled down!!)
- If desperate, replace pads, but new pads don't seem to stay scream-free for much longer than properly cleaned pads. Plus replacing these every couple of weeks could get expensive.

For discs:
- Wipe with clean cloth and brake cleaner, wipe again with dry cloth
- Sometimes additionally before bedding in again: lightly score up the surface with clean sand paper, wipe down

When cleaning, a fine black powdery deposit comes off. I guess this is your standard oil/grease contamination.

So where could the repeated contamination come from? I can only think of two things:
- Grease spraying up from the street? Sadly, I mostly use the bike for commuting. If this was the problem, however, how could any road bike work long-term with discs?
- Brake fluid leaking onto the pads?? I've tightened up what I can. Doesn't seem to have helped.

Any thoughts on the cause of the repeated contamination?


Turbo Levo 2020, Shimano SLX M7120, 4-piston caliper, standard Shimano D02S metal pads

 

[DeRailled7]

Hi, first thing to note is that metal pads are noisy by nature. Not always but they scream a bit more than resin. For your next set you could try resin pads. For commuting you likely don’t need the stopping power of the metal pads. If you live in a humid climate, a little of condensation on the rotors will made them scream until they warm up and water evaporates.
Next, it’s possibly fluid leaking from the callipers. I had that problem with one of mine. Same brakes as yours. For me oil was leaking at the connection between the hose and the calliper. Solution was to disconnect, cut hose just above olive/nipple, make sure nice clean cut, install new olive/nipple and reinstall. The way i found out where the leak was, was by thoroughly cleaning the calliper all around, go for a ride and do a detailles inspection.

 

[Gary]

If you've checked for obvious leaks/wetness on the caliper from the hose etc. your caliper pistons could still have a micro leak. It's actually quite common on Shimano calipers and very difficult to spot. Whether this happens from a damaged seal, damaged piston or poor tolerances I could not say. But Shimano will warranty their calipers for this fault.

Also I've no idea what your roads are like but all weather year round UK commuting absolutely fucks calipers and pads. Causing way more corrosion than off road riding due to salt and crap being sprayed from the wet road and vehicles. pads also rarely get properly hot to bed in properly and have a tendency to glaze.. Lose braking power and become noisy.

 

[steve_sordy]

By any chance do you transport your bike on a tow bar rack? As soon as I started doing so in the damp weather, the road crap came up onto the discs and I got your problem. So I used sandwich bags to cover the discs, problem solved. Very low cost; free if you recycle the ones that have already been used. The amount of watery brown coloured droplets that are on the bags when I get where I'm going can be surprising!

It only works if the cut side is downwind, otherwise the slipstream inflates the bags and rips them clean off.

PS: The photo above was taken purely to satisfy someone on here who could not visualise what I meant. I don't actually put the bags on until the bike is on the rack.

 

[mak]

By any chance do you transport your bike on a tow bar rack? As soon as I started doing so in the damp weather, the road crap came up onto the discs and I got your problem. So I used sandwich bags to cover the discs, problem solved. Very low cost; free if you recycle the ones that have already been used. The amount of watery brown coloured droplets that are on the bags when I get where I'm going can be surprising!

View attachment 82926

It only works if the cut side is downwind, otherwise the slipstream inflates the bags and rips them clean off.

PS: The photo above was taken purely to satisfy someone on here who could not visualise what I meant. I don't actually put the bags on until the bike is on the rack.

Is it really that time consuming and involving? Surely you could wrap the thing up in cotton wool to arrive at a destination in pristine condition only to be 2 mile into a shit hole of a trail. Whats the point?
You cant help brake squeal on a wet and muddy trail, I can deal with that , brake contamination for me is when oil or silicon spray has got onto the pads reducing brake bite.

 

[Mikerb]

Whenever I clean/lube my bike I wrap the discs and callipers in paper towell. The only time I clean pads or rotors is when I service the calliper pistons. Like all sintered pads I get a couple of squeals after they get wet but usually only for one application of the brakes.
For commuting use you may well be better off using resin pads simply because you are unlikely to get/keep sintered pads hot enough to stay clean and if your commute is in heavy traffic there are lots of contaminants.

 

[steve_sordy]

Is it really that time consuming and involving? Surely you could wrap the thing up in cotton wool to arrive at a destination in pristine condition only to be 2 mile into a shit hole of a trail. Whats the point?
You cant help brake squeal on a wet and muddy trail, I can deal with that , brake contamination for me is when oil or silicon spray has got onto the pads reducing brake bite.

It is neither time consuming nor involving.

I don't care about wet & muddy holes on the trail causing temporary brake squeal, what I am avoiding is the oily contamination thrown up from the road en route to the trail. I know it is crap from the road and not from my exhaust because the problem only happens when the roads are damp. You should see the state of the sandwich bags sometimes. Since I started to use the bags, the only time I get any brake squeal is after a soaking of the brake area during a ride. That is easily fixed by a touch of hard braking, or a few seconds dragging the brake whilst still pedalling. But after road contamination the squeal was with me for the rest of the ride, followed by brake pad decontamination routines that frequently failed.

As for being time consuming and involving; it takes 10 seconds per bag to cut one side of each bag. I can use the bags multiple times and it only takes another 10 seconds or less per side to fit and even less to remove. I believe that effort is worth it to avoid 3 hours or so of brake squeal and the necessary decontamination work. It works for me.

 

[Mikerb]

Muc-Off Bolt Disc Brake Covers, Set of 2 - Washable Neoprene Protective Covers for Bicycle Disc Brakes - Protects From Overspray And Damage In Transit : Amazon.co.uk: Automotive

 

[Tim1023]

Thank you for the input guys!

In answer to the various questions:
- I live in Hamburg and I do believe that they put salt on the roads. Hasn't been much need for it this winter, but last winter went down to minus 12 here, so some damage may have been done then.
- I do put the bike on the back of the car, but haven't done so for a while.
- I initially thought that those Muc-Off covers were just for those with too much money (and that from Mr All-The-Gear-And-No-Idea), but have recently bought a pair to avoid crap getting onto the brakes during washing and transport.

Interesting to hear that brakes leaking fluid is really a thing. I wasn't sure. I'll give the calipers a good clean as well as closely inspect after riding to see if I can see evidence of new fluid where is shouldn't be.

 

[steve_sordy]

Muc-Off Bolt Disc Brake Covers, Set of 2 - Washable Neoprene Protective Covers for Bicycle Disc Brakes - Protects From Overspray And Damage In Transit : Amazon.co.uk: Automotive

My sandwich bags are free! I only use them after they have already been used for something else.

 

[Stihldog]

Condoms for brake calipers…I’m gonna look for those at the Bike Show this weekend.

 

[steve_sordy]

Condoms for brake calipers…I’m gonna look for those at the Bike Show this weekend.

You use sandwich bags for condoms? Watch that the ziplock doesn't get caught in anything!

 

[cozzy]

Depends where you keep them. I keep mine in the kitchen and eventually realised it was likely the general kitchen cooking grease/grime that builds up on the top of the cupboards contaminating them.
I keep the discs covered now.

 

[High Rock Ruti]

Since I've had the bike, I've repeatedly had problems with screaming brakes. I've come to the conclusion that it's simply contamination. On the rear brake, I put this down to careless washing on my part transferring crap from the drive train. Both front and back brakes have similar problems.

However, even when I clean all brake components to within an inch of their lives (including replacing the pads, rubbing down the discs and bedding in), the problem only stays away for a few days before I need to do a deep clean again.

Cleaning regime for pads:
- Clean with brake cleaner, sand down, clean again
- Sometimes additionally: dowse with brake cleaner, set alight, let it burn for about 20s, clean again (once they've cooled down!!)
- If desperate, replace pads, but new pads don't seem to stay scream-free for much longer than properly cleaned pads. Plus replacing these every couple of weeks could get expensive.

For discs:
- Wipe with clean cloth and brake cleaner, wipe again with dry cloth
- Sometimes additionally before bedding in again: lightly score up the surface with clean sand paper, wipe down

When cleaning, a fine black powdery deposit comes off. I guess this is your standard oil/grease contamination.

So where could the repeated contamination come from? I can only think of two things:
- Grease spraying up from the street? Sadly, I mostly use the bike for commuting. If this was the problem, however, how could any road bike work long-term with discs?
- Brake fluid leaking onto the pads?? I've tightened up what I can. Doesn't seem to have helped.

Any thoughts on the cause of the repeated contamination?


Turbo Levo 2020, Shimano SLX M7120, 4-piston caliper, standard Shimano D02S metal pads

High Rock Ruti

My 2022 Turbo Levo Pro has sram metal pads and they've been noisy, not screeching but annoying just the same. I doubt your pads are contaminated with all the cleaning you've given them. I call sram, shimano and maxxis they're all really happy to talk shop.

Warm Regards Ruti

 

[1oldfart]

I pedal 350 days, sun, rain, snow and my brakes are silent.
Sometimes they sing. I do nothing, it goes away.
It is more frequent in winter(fatbike) it is just humidity.
We use it like a bell letting others know we are there.
Try doing nothing it might work.

 

[Tim1023]

I'm pleased for you! Doing nothing is the default case until problems arise. In my case, doing nothing (with the brakes) = screaming gets louder.

Interestingly, I never had brake problems on my old Stumpy, but my gears were a pain to maintain. On my Levo, it's the other way around. The gears have been a dream.

 

[Orangie]

Had seeping calipers do that

 

[Tim1023]

I've just swapped my commuting wheels for my knobblies and as part of that inspected the brakes that I had thoroughly cleaned a couple of weeks ago. Not only were the brake pads covered in soot again, but one pair was noticeably wet on the back.

So that looks like an open and shut case for seeping calipers! Round to the LBS next week.

Thank you for the tip to look out for this. Didn't know it was a thing beforehand.

 

[Tim1023]

Finally managed to get an appointment with the dealer for them to have a look.

They said that they ran all sorts of tests (e.g. pressure tests to make sure the seals held) and said that they couldn't find anything out of the ordinary. And they replaced the metal pads with resin ones. They asked me to take a bunch of photos should the issue come up again. Sceptical, I rode home. Around 15km

Next morning, screeching again. I took some photos including these:

... bike went back to the dealer. A fluid leak couldn't be denied!

Now convinced that there was, indeed a leak, they swapped the brake unit out for a new one. I've only done around 60km on them, but thus far, silent bliss!

They also sent the original to Shimano and promised to let me know what Shimano says. Should it be anything interesting other than "yeah, a dud unit", I'll let you know.

 

[Stihldog]

A friend suddenly had the screeching sound from the front brake. (Magura mt7 performance pads) . These were broken in properly (several rides) and new. We suspected a leak in the calliper or incorrectly adjusted/alignment of the caliper housing. Nope. We believed that some contamination likely happened. We changed the pads, cleaned the rotor and calliper and haven’t heard the screeching since. We don’t know where the contamination came from.

 

[RickBullotta]

A friend suddenly had the screeching sound from the front brake. (Magura mt7 performance pads) . These were broken in properly (several rides) and new. We suspected a leak in the calliper or incorrectly adjusted/alignment of the caliper housing. Nope. We believed that some contamination likely happened. We changed the pads, cleaned the rotor and calliper and haven’t heard the screeching since. We don’t know where the contamination came from.

Many times it's being overly "enthusiastic" when lubing the chain. A little bit of chain lube finds it's way onto the rotors and you're screwed.

 

[Stihldog]

Many times it's being overly "enthusiastic" when lubing the chain. A little bit of chain lube finds it's way onto the rotors and you're screwed.

I haven’t ridden over a fellow rider who uses too much hair-gell …yet. That could be a source of contamination .
I don’t think I could trust any spray or aerosol lubricants applied on an installed chain, regardless of the precautions. Once I lube a chain(wet or dry lube) I wipe off any excess lubricant after a few shifting cycles. I’m not sure if there’s anything else I can do to prevent brake pad contamination. But it can happen.
Remove pads during bleeding, wear rubber gloves when handling brake components, positive atmospheric pressure in my garage (expensive), or common sense (cheap but difficult to find).

 

[RickBullotta]

I haven’t ridden over a fellow rider who uses too much hair-gell …yet. That could be a source of contamination .
I don’t think I could trust any spray or aerosol lubricants applied on an installed chain, regardless of the precautions. Once I lube a chain(wet or dry lube) I wipe off any excess lubricant after a few shifting cycles. I’m not sure if there’s anything else I can do to prevent brake pad contamination. But it can happen.
Remove pads during bleeding, wear rubber gloves when handling brake components, positive atmospheric pressure in my garage (expensive), or common sense (cheap but difficult to find).

Interestingly I don't shift my bike anymore when working the chain lube in - I keep it in the smallest cassette cog to keep it as far away from my brakes as possible! Yeah, maybe I'm a little too paranoid but...

 

[Stihldog]

Interestingly I don't shift my bike anymore when working the chain lube in - I keep it in the smallest cassette cog to keep it as far away from my brakes as possible! Yeah, maybe I'm a little too paranoid but...

I understand this could happen. I lube in mid-cassette and slowly distribute the lube to high and low gears. After the initial wipe of lube from the chain, this seems to distribute a very small amount of lube thru the jockey wheels and cassette. (Very small amount). Regular maintenance of the drivetrain helps too. Seems to work for me but if there’s a better method I’m all ears.

 

[RustyIron]

I've come to the conclusion that it's simply contamination.

a fine black powdery deposit comes off. I guess this is your standard oil/grease contamination.

Before a ride, I dribble lube onto the chain as I turn the cranks by hand. Detailer/wax spray is applied in close proximity to the rotors. When I finish with a ride, my bike is covered in dirt, grime, hydration drink, mud, sweat, plant debris, and sometimes even coyote poo. Magically, my brake rotors are always perfectly clean, untarnished by any of these nasty "contaminants." The brakes run fine.

Perhaps it's time to revisit the assumptions regarding the impact of "contaminants" on brake performance. Just sayin'...

 

[Stihldog]

Before a ride, I dribble lube onto the chain as I turn the cranks by hand. Detailer/wax spray is applied in close proximity to the rotors. When I finish with a ride, my bike is covered in dirt, grime, hydration drink, mud, sweat, plant debris, and sometimes even coyote poo. Magically, my brake rotors are always perfectly clean, untarnished by any of these nasty "contaminants." The brakes run fine.

Perhaps it's time to revisit the assumptions regarding the impact of "contaminants" on brake performance. Just sayin'...

I guess we can do the best we can with a bit of common sense.
( I’m not too familiar with coyote poo but bear scat tastes awful )
Contaminated brakes suck though. I’ve been lucky so far. Not my neighbour though.

 

[Paul Mac]

100% it's those Shimano Do2 pads.
I've just renewed my discs and pads with exactly what you have.
They scream all the time, as soon as they get either wet or dusty.
I've done everything you have done, sanding cleaning etc, they shut up for about 10 mins and start again.
I've never had this ever on my bike before.

 

[Mikerb]

I wrap shop towel around my rotors and callipers whenever I clean/lube my bike.

 

[2WheelsNot4]

Whenever i see threads like these i look for the magic word in the post

"Shimano"

 

[1oldfart]

Whenever i see threads like these i look for the magic word in the post

"Shimano"

In many years only ounce i had a contaminated disc.
The shop made a mistake and it was on a SRAM system.