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The disk brakes practically don't brake anymore. If I pull the brake lever as hard as I can, the wheel still turns if I push the bike forward.

Is this normal? Do they need a "brake in" period?

UPDATE: It's a mechanical brake, and the levers are properly adjusted. If I pull the brake lever, I can see the pads pressed against the rotor, but the wheel still turns slowly If I push the bike. This was not happening before.

The maintenance was done at a local bike service, I don't know exactly what they did to the brakes, but the rotor seems to be oiled up.

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possible duplicate: Do I need to change my disc if the brake pads got oil on them –  Vorac Aug 15 '13 at 12:27
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If I paid for brake maintenance I would expect my brakes to work perfectly when I got it back. I would take it back to the shop that did the work. –  Carey Gregory Aug 15 '13 at 15:12
    
@Vorac: The duplicate you refer to the OP got the oil on them himself, in this case, the LBS did it. –  mattnz Aug 17 '13 at 4:33
    
I am always impatient to learn how things worked out in the end. –  Vorac Aug 27 '13 at 12:34
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@Vorac: I've personally cleaned the pads/rotors using alcohol and sandpaper using the procedure from a link around here, then bedded them in. Now it's much much better, but they still don't break quite like before. Maybe more use is required. –  Adal Aug 29 '13 at 23:31
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4 Answers

up vote 3 down vote accepted

If the pads have oil on them they need replacing. The discs can be cleaned if done properly and carefully. If the LBS did the work, take the bike back and they should put it right.

From the sound of it, I would also be looking for another LBS. If they cannot service brakes and keep the oil off they are at probably sloppy - but even the best shops have the odd incident. However, as they returned the bike to you in that condition, it is dangerous, they have let poor work out the door. My future custom with them would be in serious jeopardy.....

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"Outrageous" might be a proper word in this context. It goes without saying that if the mechanic accidentally puts oil on your brakes, while he is being payed for maintenance, he must replace the rotor and pads at his expense! –  Vorac Aug 16 '13 at 8:25
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Two possibilities as I see it.

1) the pads haven't bedded in yet. It takes a good handful of hard stops before a new set of pads start stopping you well. Go out on the street in front of your house and speed up and pull the levers hard a few dozen times.

2)the brakes arent actually properly adjusted and the actuator arm is bottoming out. Mechanical disc brake calipers basically act like a screw to press the brake pad against the rotor. This is done by the cable being attached to an arm on the caliper that turns the "screw". It is important that the cable is properly adjusted for this to work. One one side of the caliper (or both, depending on your model of brakes) there will be a knob that you can turn that will move the pad in toward the rotor independently of cable tension. Some folks adjust the cable in too far instead of using these knobs to adjust the pads. You can test this by taking your wheel out and pulling the appropriate brake lever. If the lever still stops at nearly the same point that it did when the wheel ws in, then you've found your problem and you need to take the bike back to the shop to have the brakes adjusted properly.

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It sounds like you haven't adjusted the brakes after you carried out maintenance. You haven't described what you did, but I'm assuming you adjusted the cables from your levers to the pots? If so you probably need to pull them a bit tighter - there will be an adjustment screw at each end.

Also read this question on bleeding hydraulic brakes.

And as per your update, if you have oil on the rotors, then your brakes will not grip. Follow the link Vorac provided.

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I've updated the question –  Adal Aug 15 '13 at 12:26
    
Could also be that the pads are worn out and are not actually causing any brake force/friction. Try sanding the pads lightly to rough them up and see if the braking improves. –  Aaron Aug 15 '13 at 14:01
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@jm2 is the correct answer I would say. If there is oil on the pads then braking hard with them will just create heat and melt the surface of the pad, forming a shiny layer. This can be fixed by using white spirit and a little sand paper. Clean your disks with white spirit also.

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