Disc pads keep getting contaminated - help

[Luegolover]

Hello,

I have a road bike with the R785 hydraulic disc system and I am having trouble with the front disc pads. The pads keep getting contaminated and then squealing whilst working ineffectively. If I clean and sand the pads and the disc then the brakes are beautiful. However within about 20 miles the front starts to become ineffective and also squeals. When I remove the pads they have a dark glossy coating. It almost feel like the calliper is leaking and then covering the pads however, I have not had to replenish the reservoir.

Any ideas on what the cause could be?

Regards
Steve

 

[fossyant]

Dunno. Are these Shimano pads, or copies ?

 

[flyingfish]

I had a problem similar to this caused by weepy tektro calipers. Just a little oil was getting on the pads

 

[lpretro1]

Sounds like the pads are glazing - when you fit new pads you need to bed them in to burn of a layer of chemicals thaty are there from the manufacture process. This requires a goodly series of hard, fast stops to get enough heat into the brake to do so. Gentle braking will not be sufficient and will cuse the glaze and pads become ineffectual.

 

[Globalti]

There is no layer of chemicals from the manufacturing process. Some people believe that several sessions of hard braking will somehow help to "bed in " the pad to the disc or affect the metallurgy of the interface, which may be true but isn't very well understood. Your best bet is to put the pads in the dishwasher to get them thoroughly degreased and to clean the disc AND the caliper with something like IPA, ethanol, glass cleaner or very hot water and detergent so as to remove any oil or brake fluid.

 

[Milkfloat]

I would also consider your maintenance - I assume you are not letting any oils, WD40 etc get anywhere close to your discs or pads? I have never been able to completely clean contaminated pads, I have always had to resort to new ones.

 

[Mobytek]

/\/\ new pads.

Contaminents come in many forms but have he same effect. If you cahnge your pads you can then have a carte blanch to check from weeping pistons etc.

But also remember - roads have a lot more oily / diesel / fuelish substances, and these float readily on water, when it rains, so in road spray, they are straight onto your pads.

dont get that amount o oil on a MTB track.

Perils of disks on road - not a good mix for day to day, but good for pro;s on closed, cleaned roads!

 

[Drago]

But also remember - roads have a lot more oily / diesel / fuelish substances, and these float readily on water, when it rains, so in road spray, they are straight onto your pads.

Especially true if you've spent any time stuck in traffic behind a VW.

 

[Bobby Mhor]

I had the same kinda thing and found a caliper was leaking fluid...

 

[Luegolover]

Thanks for the helpful replies.
They are Shimano pads, discs, callipers and fluid so I am comfortable that I have done the correct thing there.
I am not an expert mechanic but I am comfortable with the way I work on the bike with regards to the braking area and am sure that no oil or contaminants are getting in to the pad area from that. I use muc-off but do not put it near the brakes/hubs so doubt if that is causing it.
I am also aware of the braking in process and coupled with the fact that the back brake works wonderfully I doubt I have got it miles wrong there either.

I did think that the pads were possibly showing signs of fluid on them and suspect that this might be the cause but as mentioned I have a full leaver so doubt much can have leaked. I will look at that though as I can't see it being anything else.

Cheers

 

[rusty bearing]

Regarding the 'no layer of chemicals, this from a disc pad manufacturer is probably what retro was meaning.....

Breaking-ins or Bedding-in does two things. The first is to burn off chemicals and resin left on the pad, and secondly to lay down a transfer layer or transfer film between the pad and rotor. As you may have already read that EACH and EVERY one of our brake pads goes through the Thermo Scorched process, which helps burn off chemicals and resin left behind on the brake pad after its manufactured. We still want that transfer layer to go on the rotor. We recommend you to-break-in or bed-in your new brake pads, but your brakes will still work should you choose not to go through this process.

As for heavy braking, the Sram tech docs for example recommend it in there pdf
https://www.sram.com/sites/default/files/techdocs/xxwc_xx_xo_service_manual_rev_b.pdf.

 

[Mobytek]

bedding in really does have a difference. some say a lot, others say less, but the heat can change the compound slightly, at least the surface layer