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Weak disc brake
#1
Back disc break on my Orbea commuter got much weaker this week. Front break is strong as always. I dont think that smth special happened, like crash, that damaged the brake.

Never worked much on disc brakes. I want to fix this myself but I dont know where to look first and dont want to mess smth up. Where should I start? I have Shimano mech disc brakes.
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#2
how old and aprox. miles on them? Did you possibly get any oil on the pads/rotors. If they are new, the housing and cable may have seated in and you just need to re connect the cable tension. make sure all housing is properly seated in the cable stops.
There are two kinds of people in the world, "Those who help themselves to people, and those who help people!"
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#3
It is new, got last summer. In other words only few months old and only +|- 250 miles biked. I lubed chain a week ago but must not be a problem, right?. Do I first check out the lever or go straight to caliper where the cable is in grip?
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#4
With any brake you need to adjust for pad wear (and cable stretch, which is more of a factor in the rear - unless you have hydraulic disc brakes, no cables to stretch there...). Depending on riding conditions and braking habits pads can wear out even within a rather short distance (ok, heavy mountainbiking with lots of technical descents). Check for pad adjustment possibilities on your brake. Pad wear should not be corrected by cable tension, depending on the brake this can cause you to crash as the brake fails!

Explanation: some brakes have captured balls that are moved up a ramp on a rotating disc. As they move up the ramp, they push the brake pads inwards. Rotation of the ramp is caused by pulling on the brake cable. Problem is that the ramp has a finite length and when you run out of ramp either the brake just does not engage more or even fails completely.
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#5
(01-05-2020, 01:14 AM)brno Wrote:  It is new, got last summer. In other words only few months old and only +|- 250 miles biked. I lubed chain a week ago but must not be a problem, right?. Do I first check out the lever or go straight to caliper where the cable is in grip?
I would start by cleaning and check pad for wear. you did not mention squealing which is an indicator of contamination but would not rule it out. Many bicycle shops offer a post purchase check up, if yours does let them have a look. If a good cleaning of the rotor and pad scuff does not work then replace the pad and clean rotor again.
There are two kinds of people in the world, "Those who help themselves to people, and those who help people!"
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#6
(01-05-2020, 02:50 PM)Painkiller Wrote:  you did not mention squealing which is an indicator of contamination but would not rule it out.

zero squealing ...

Thanks @Painkiller and @Joe_W! I will start wihth pad wear inspection and then cable stretch. Expect updates from me.
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#7
good luck and look forward to your results
There are two kinds of people in the world, "Those who help themselves to people, and those who help people!"
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