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My Mech. disk brakes work really crappy.

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My Mech. disk brakes work really crappy.

Old 06-30-08, 02:25 PM
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Day-5
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My Mech. disk brakes work really crappy.

Ok I bought a second hand bike and I completely repared it. But my disk brakes (mechanical) break only a bit. I took it to parts and cleaned everything. The slides inside are like new still about 1 mm left. So do u have some advice? I was thinking about buying hydraulic ones but still.. I dont want to waste more and more money if it can actually work. Thanks.
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Old 06-30-08, 02:33 PM
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What model/brand do you have?
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Old 06-30-08, 02:35 PM
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Slides? If you refer to the pads, Park says Avid pad+backer plate should be at
least 3mm thick. That is not likely to be much different for other systems.
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Old 06-30-08, 03:17 PM
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Ok sorry pads english is not my first language... The brand is shimano and I think the pads are fat enough because the "stone" or whatever it is still there and touching it. Or should I just buy new pads or new brakes? The situation is simple. I press the brake and I press it real hard but the disk stops really slowly. Its breaking but its not enough. I was thinking about that maybe that there should be something on the pads or on the disc... But I dont know. And model I dont know cause its night and im lazy to go out and check it out:-).
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Old 06-30-08, 04:00 PM
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The (fairly cheap) mechanical disk brakes that I've seen have one fixed pad on the inside of the rotor and one moving pad on the outside of the rotor. The fixed pad's position can be adjusted (often using an allen (hex) screw on the inside of the caliper assembly); having the brake wire correctly tensioned keeps the moving pad in position. It sounds like your brake caliper needs new pads and/or some minor adjustment.
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Old 07-01-08, 06:46 AM
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Yea well you are right they are cheap I think and I will just buy new ones...
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Old 07-01-08, 07:16 AM
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don't touch the rotor or the pads with your fingers when you get your new ones. any bit of oil from your hands (or chain lube etc.) will ruin your disc brakes and make them less effective.
I recommend AVID bb7 or for a cheaper budget AVID BB5 these are GREAT mechanical disc brakes.
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Old 07-01-08, 01:04 PM
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The Shimano mechanicals may be lower end items but they certainly should work better than this.

As mentioned above but I want to stress it again it is super important with any mechanical brake that the fixed pad on the spoke side is adjusted to where it is extremely close to the rotor. You want to adjust it so that it is actually skimming the rotor and then go back only just barely enough to avoid the skim sound. And this means maybe 1/10 of a turn or less on the adjuster at that point.

If the rotor skims at some parts of the turn but not others you can gently but firmly flex the rotor to even it up so the inward touching parts are now flexed outward a hair. Or do a combo of flexing the touching part and the CENTER area of the non touching part. This is a fussy bit of adjustment but you'll find that you need to do it with any disc brake that has one side fixed if you want to get the best performance from them. Even the more expensive ones.

You also want the caliper to sit so the pads contact the entire face to the rotor all at once and very evenly. To set that I hold the brakes on hard with one hand and loosen the screws at the caliper to the mounting adapter about a full turn. THen wiggle the caliper a little so the rotor moves and hold it in place. Then tighten down the screws going back and forth to sneak up on the final tightness. If you try to do one all the way it'll twist the caliper around and you're back where you started.

All this is part of any disc brake system. Even the hydraulic ones need to be set up like this so the calipers are accurately centered.

If they calipers were not set right in the first place then the pads are very likely worn to a shallow curve or angle. Use a metal ruler on the face of the pads and sight along the line with a light behind looking for a very slight curve or hill in the pad faces. Anything at all means you need new pads.

The rotor should also be cleaned with some brake cleaner and paper towel now and then to ensure there's no oil, wax or anything else on it. I wouldn't say that it's so sensitive that you can't touch the pad or rotor faces but when doing this sort of work I go and freshly wash my hands to ensure there's no oils or greases from the other bike work on them. And while working with them I do try not to touch those faces just as extra insurance. Certainly any sort of oil or grease on the pads and you'll be in for a lot of troubles.

What you should do is first get new pads so you KNOW they are flat. Second is mount them and then do the alignment trick with clamping and resetting the screws. THen use the fixed pad adjustment and any gentle rotor flexing as needed to get it running in close contact.

If in doubt it's better to have a light skimming sound. Not enough to drag it to a stop but just so it kisses the rotor. After a ride or two the fixed pad will wear enough to make the sound go away and you'll have a perfect gap.
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Old 07-02-08, 10:42 AM
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Thanks for your work u had to spend like 2 hours to write that :-). I workin on it now... But I found many good advices over there thanks dude.
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Old 07-02-08, 10:47 AM
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Yea it works much better now.
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