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Contaminated brake pads???

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[#13536533]

I’ve recently had to change my front disc pads twice due to them not working with no signs of obvious contamination on the rotor or pads. There’s no hydraulic oil leak that I can see, I’m confused why they’ve stopped working? They squeal and don’t do much. 

I’ve bought some Aztec organic pads from Tredz, has anyone used them before and had any issues with them?

 

I can’t see anything oil leaking from the caliper so I’m confused why they’re contaminated, I doubt it’s from being picked up on the trail. Anyone got any ideas? Or a case of buying better pad? If so what do people recommend?


 
Posted : 01/08/2026 6:58 pm
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Do you transport your bike by car? Internally or externally? Roof or rear?


 
Posted : 01/08/2026 7:01 pm
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Knowing which brakes would be good too

Aztec are fine, the sort of brake pads you buy when no others are available 

They squeal and don’t do much. 

This certainly sounds like contamination


 
Posted : 01/08/2026 7:19 pm
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Grubby/ oily hands in the rotor? 

If you've an electric hob leave them on a low the heat till they start smoking. Let them cool, some <180 grit sandpaper and rough them up (or scrape them on stone/concrete). Wet them and rub the pads together. 

Clean the rotors.

Bed in the pads again.


 
Posted : 01/08/2026 7:55 pm
Tracey reacted
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I’ve had it before where there was no obvious leak, but in the end up confirmed as a micro leak (shimano zees). Not always easy to pick up 


 
Posted : 01/08/2026 8:18 pm
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Shimano Calipers? If so, they will be leaking. 


 
Posted : 01/08/2026 10:18 pm
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I get this with older Shimano brakes on bikes that haven't been used for a while (usually my commuter bike). The scrub rotor and pads with washing up liquid then heat the pads with gas flame until they stop smoking always sorts it out. No need for new pads. Assume the same will work with any contaminated brakes\pads.  


 
Posted : 01/08/2026 11:29 pm
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What's your bedding in process ?. Though sqealers is usually contamination.

Test that out. Put a little bit of paper behind the pads. It it leaves a ring, that usually means theres fluid getting out.

 

Which brake and model is it ? Shimano had a problem for a while with some calipers leaking**.I know you said not, but might have missed something.

** could leaking come from elsewhere outwith the pads/pistons. As in hose connection, and something is dripping into the caliper or even the rotor.

 

Other options - Check caliper alignment. 

If you've an electric hob leave them on a low the heat till they start smoking

Good point, and if theres no smoke its not contamination.


 
Posted : 02/08/2026 4:00 am
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How do you clean the rotor?

How do you bed the new pads in?

How frequently is the bike used?


 
Posted : 02/08/2026 7:08 am
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I’ve got Shimano Xt brakes, don’t handle the rotors in any way apart from I’ve had issues with the pads.

I clean them with Peatys disc cleaner spray. 

i use the bike once a month maybe more at times and cycle to get onto Dartmoor and rarely in the back of a van to got to south wales. 

I don’t always bed them in but I’ve never this issue before on this bike, which is only 2 years old. 


 
Posted : 02/08/2026 10:05 am
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I thought this once for quite a while.

I eventually noticed that the calipers moved over time and needed realigning again as I was only getting proper contact on oneside and more noticeable in the wet which felt.like containimation. 

Tissue and overnight taping the brake on can help see if tiny leaks as well. I did this which proved no leak.


 
Posted : 02/08/2026 12:50 pm
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Posted by: Aggs2

I thought this once for quite a while.

I eventually noticed that the calipers moved over time and needed realigning again as I was only getting proper contact on oneside and more noticeable in the wet which felt.like containimation. 

Tissue and overnight taping the brake on can help see if tiny leaks as well. I did this which proved no leak.

 

What about the fact, once you’ve changed the pads it works like they did?

 

I also noticed when I was out last week,when I found out the brakes were shocking, I poured some water from my camelbak over the calliper and pads and they worked better, any ideas?

 


 
Posted : 02/08/2026 3:00 pm
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Water adds friction. Once it evaporates you're back to where you were before. 

 

Tried cleaning the pads? 

 

Isopropyl alcohol or decent heptane beagle cleaner.


 
Posted : 02/08/2026 3:10 pm
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Cleaned the pads and rotors with Peatys Disk cleaner salary, surely that should be good enough?


 
Posted : 02/08/2026 3:23 pm
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Also is it best to sand the pads a bit before putting back on the bike?


 
Posted : 02/08/2026 3:28 pm
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I had a couple of duff sets of Aztec pads a while back. Swore never to buy them again.


 
Posted : 02/08/2026 3:52 pm
dyna-ti reacted
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I only use water to clean my rotors, no idea what is in Peatys spray so no idea if it is leaving a residue on the rotor.

Sand the pads but then make sure they are properly bedded in...pads that don't get bedded in are never as good/effective as pads that do get bedded in.


 
Posted : 02/08/2026 4:25 pm
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I'd skip the brake cleaner too - apart from a bit of water my rotors and pads don't get touched at all. I've recovered pads using a gas flame before - top tip is to use a camping stove outside cos they stink something rotten when you're burning off the muck.

Posted by: kernowgaz
What about the fact, once you’ve changed the pads it works like they did?

You'd have pushed the pistons back so may not notice the lazy piston until the pads have worn a bit. It's usually an easy fix - just hold one piston in and squeeze the brake a few times to extend the other one,, push that back then repeat for the other side then check they both move evenly when you pull the lever. Just be careful not to pump the piston too far out as that will end in tears.


 
Posted : 02/08/2026 5:01 pm
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Good point about the lazy piston.  I had this a long while back. 


 
Posted : 02/08/2026 7:29 pm
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If you have changed brand and cleaned the rotor it may take a while for some of brake pads material to transfer to the rotor.

Cleaning the rotor /every/ time will restart the process 


 
Posted : 03/08/2026 11:15 am