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Squeaky and ineffective hydraulic disc brakes

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Squeaky and ineffective hydraulic disc brakes

Old 07-27-18, 09:06 AM
  #1  
duffetta 
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Squeaky and ineffective hydraulic disc brakes

Long story short, I just replaced the rotor and the pads on my Shimano BR-M447 hydraulic front brake. It worked great (quiet and full stopping power) for two rides (I commute daily 6 miles each way). This morning, after riding home in a rain storm yesterday, the front brake is again very noisy and has lost its stopping power. What's going on here?

Longer story: I had worn my pads down to nothing recently, so I stopped in to my local bike store who sold me Jaguar pads. I believe that they were resin, but I can't be certain. I replaced the pads, and went on my way. Both brakes, about 2 days in on the new pads, starting making horrible squeaking noise and lost their stopping power. I tried cleaning the discs with isopropanol, with no affect. At that point, I decided to just get brand new Shimano rotors and matching pads. I had time to do the front the other night. For those results, see above.

What is going on here? Why do the brakes become ineffective after two rides?

Thanks,
Mark
--
2017 BMC AlpenChallenge AC02 Alfine 8 (with Gates drive)
2015 Fuji Gran Fondo w/Shimano 105 (11 speed)
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Old 07-27-18, 09:10 AM
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You mean Jagwire pads?
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Old 07-27-18, 09:12 AM
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is it possible you or the bike shop got some kind of oil or grease on the pads ? a spray on chain oil maybe ? even the natural oils on your fingers could be enough

I have taken out my pads and held them with a needle nose pliers in the flame of my camping cooker . Any oil on them will burn off as smoke . As soon as smoke dies down take them out .I wouldn't hold them in the flame for longer than you need to . Try not to handle the contact side of the pads with your bare hands .

The rotors can be cleaned with isopropyl alcohol
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Old 07-27-18, 12:57 PM
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Yes, Jagwire, sorry.

I did the work myself. The new pads went straight from the package to the brake housing (after inserting the spring), so they are BRAND new, just as is the rotor (straight from the package to the wheel). I did use a tiny amount of triflow on the threads for the rotor, but none got on the rotor surface.
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Old 07-27-18, 01:53 PM
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I have had good quiet performance from Kool Stop 'organic' compound pads ..
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Old 07-28-18, 12:19 AM
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Remove the pads and check the back of them. Is there any mineral oil there? It's not particularly common, but some Shimano brakes have developed problems with the pistons leaking, which causes brake contamination. If you have proof of purchase within the last 2 years it's an easy warranty with Shimano, if not you'll have to replace the calipers (or the whole system). Shimano does not sell piston overhaul kits.
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Old 07-28-18, 05:55 AM
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The pads and the rotors could (and probably are) not best friends yet. Heed the advice of the others and clean off the pads and rotors first, then bed in the brakes. Park Tool has a video on how to do this IIRC.
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Old 07-28-18, 11:03 AM
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bleed the brakes.
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Old 07-28-18, 01:39 PM
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Another hint. My local bike shop suggested that my storage of the bike hanging from the front wheel may be cause the brakes to leak. They are having a look.
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Old 07-29-18, 11:37 PM
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Originally Posted by duffetta View Post
Another hint. My local bike shop suggested that my storage of the bike hanging from the front wheel may be cause the brakes to leak. They are having a look.
People have all sorts of ideas and can be pretty good mechanics--but this is unlikely to cause problems. If anything it an be helpful to get air to move upwards from the rear caliper to the lever.

Leaking at the calipers seems to occasionally happen when bikes sit for long periods of time without use, and also as the result of damaged or faulty calipers. Or you simply managed to contaminate something on installation.
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Old 07-30-18, 06:07 AM
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Air in the lines or hanging from the front wheel has nothing to do with squealing brakes.

Always do the easy and cheap thing first - clean the rotors, install new pads, bed them and don't wash the bike with car wash soap which can contain waxes and oils.

If the system is leaking then squealing is only a symptom, not the problem. Treat the problem and the symptom will go away. Again, always do the easy and cheap thing first.


-Tim-
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