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  1. #1
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    Disc Brake Function Question

    Hello all,

    So I was able to salvage my disc brake pads on my trek 3900 (at least the back ones for sure).

    I have a question about the front disc brakes. They do not lock up when I fully pull the lever. Is the normal. A guy at my LBS said that they should not lock up due to control reasons....and because going downhill and locking them up could prove a big bummer. Is this true?

  2. #2
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    Quote Originally Posted by oceanfirehawk
    Hello all,

    So I was able to salvage my disc brake pads on my trek 3900 (at least the back ones for sure).

    I have a question about the front disc brakes. They do not lock up when I fully pull the lever. Is the normal. NO
    A guy at my LBS said that they should not lock up due to control reasons find another shop or buy that guy a clue
    ....and because going downhill and locking them up could prove a big bummer. Is this true?YES
    what brakes do you have?
    I used to ride to Win ... Now I ride to Grin

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  3. #3
    AZ
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    They should lock up when functioning properly and in proper adjustment .

  4. #4
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    the cables on cable disc systems stretch alot, and need to be adjusted fairly often for maximum braking. i like to have my brakes adjusted tight enough to lock up if i want them to that way you just squeeze the brakes as hard as you need

  5. #5
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    Quote Originally Posted by 530_singletrack
    the cables on cable disc systems stretch alot, and need to be adjusted fairly often for maximum braking. i like to have my brakes adjusted tight enough to lock up if i want them to that way you just squeeze the brakes as hard as you need
    I have been on 4 rides with all 4 using moderate braking. Shouldn't the brakes have been broken in yet?

    I'm not sure what brakes they are. they are on the 2010 trek 3900

  6. #6
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    Quote Originally Posted by 530_singletrack
    the cables on cable disc systems stretch alot, and need to be adjusted fairly often for maximum braking. i like to have my brakes adjusted tight enough to lock up if i want them to that way you just squeeze the brakes as hard as you need
    You must be using pretty shoddy cable then. MY BB7's have only been adjusted very slightly since they were installed a few weeks ago.

  7. #7
    AZ
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    It has Promax mechanical disc brakes . Did you break them in properly ? Did you overheat them or glaze them over ?

  8. #8
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    Quote Originally Posted by AZ.MTNS
    It has Promax mechanical disc brakes . Did you break them in properly ? Did you overheat them or glaze them over ?
    please explain overheating or glazing them over. i already dried them with rubbing alcohol & lightly sanded them to get the lube off that i got on accident.

  9. #9
    AZ
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    Quote Originally Posted by oceanfirehawk
    get the lube off that i got on accident.


    Theres your problem . Take the pads out and cook them in a pan or on the barbque , whatever , cook them until they quit smoking . Clean everything else with iso - propyl alcohol . After you pads quit smoking let them cool and then sand them . Put it all back together and break the pads in .

  10. #10
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    Quote Originally Posted by AZ.MTNS
    Theres your problem . Take the pads out and cook them in a pan or on the barbque , whatever , cook them until they quit smoking . Clean everything else with iso - propyl alcohol . After you pads quit smoking let them cool and then sand them . Put it all back together and break the pads in .
    what did the other poster mean by "glaze" and "overheat" my brakes

  11. #11
    AZ
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    Overheat means exactly that , get them to hot , especially before they are broken in . Glazed over is when the brakes have contamination and the use of the brakes causes the contamination to spread across the friction surfaces rendering the brakes useless .

  12. #12
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    Quote Originally Posted by AZ.MTNS
    Overheat means exactly that , get them to hot , especially before they are broken in . Glazed over is when the brakes have contamination and the use of the brakes causes the contamination to spread across the friction surfaces rendering the brakes useless .
    i would like to know what type of pads to buy...just in case i need new ones. i have the trek 3900 disc 2010 but all the website says on brakeset is:

    Promax, mechanical disc w/Shimano EF50 levers

    where and what pads can i buy for this

  13. #13
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    Your LBS , most online retailers will have them . Your LBS is probably the best place to start .

  14. #14
    i also unicycle
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    promax disc brakes are a pain to set up and hard to keep in adjustment in most cases. bb5s or some lower (but not lowest) end tektros are my personal minimums for even recommending discs on a bike over v brakes.
    mtbr says you should know: i work in a bike shop.
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  15. #15
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    You may need to adjust the passive (right) brake pad. I am not sure, how it is supposed to be done with Promax brakes, I have Hayes mech. brakes, they have a stopper screw on the outside and an adjuster screw on the inner (wheel) side of the body of caliper.

  16. #16
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    Quote Originally Posted by xenon
    You may need to adjust the passive (right) brake pad. I am not sure, how it is supposed to be done with Promax brakes, I have Hayes mech. brakes, they have a stopper screw on the outside and an adjuster screw on the inner (wheel) side of the body of caliper.

    +1 one on this. mine were sucking terribly until i adjusted the passive pad. now they actually work properly!

  17. #17
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    For what it's worth, after reading your previous thread about getting oil on your brakes, and your most recent regarding the bike shop lying to you/bad brakes....I think you just need to spend some time as a newbie and LEARN. It's alright y'know....you bought cheaper stuff, you got oil on them accidentally, and you need to learn about disc brake systems.

    Some pads/rotors bed in after just a few rides.....I've had some BB7s that were great on ride #1. I've had other BB7s that took 8 or 9 rides to start performing. This is just a quirk of disc brakes...the rotor surface needs to get filled up with brake pad particulates in order to provide a smooth, high-friction surface. When that happens, your brakes will perform as best as they are able to, assuming they're set up correctly. Fix your oiled pad/rotor condition and keep riding...they should get better in time. It does help if you take them to a hill or parking garage and do some downhill stops....or you can just ride trails and let it happen more gradually.

    Disc brakes take more "skill" than caliper brakes....they need to be kept clean, adjusted, and proper set up in the first place is critical to both maximum stopping power and to avoiding squeal. I can't tell you how many mechanical brakes I've seen that weren't set up the right way...ridiculous. It's not hard, you just have to take the time to understand and do it right. You can do it yourself if you don't trust your shop mechanic...or find a different shop.

  18. #18
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    Agree and...

    I question why one needs to "lock up" the brakes? In front, it'll cause you to crash. In locking up the rear, you destroy the trails and invite the wrath of trail builders and good riders who will want to put your d!ck in the spokes & spin the wheels for wrecking their trails.

    Learn about modulation. think about it, do you lock up the brakes on your car?

    jc

  19. #19
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    just wondering why you want your front brakes to lock up? you mentioned on the other post that you're a newbie and imagine going downhill and you lock up your front brakes, you'll be going over your handle bars and eat dirt. that's what your lbs meant.
    2000 something DB Sorrento
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  20. #20
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    You will also have contaminated you rotor.

    Same deal, bake at gas mark 3 until it stops smoking.

  21. #21
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    Can you bake resin pads? I thought sintered only for cooking?

  22. #22
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    Quote Originally Posted by oceanfirehawk
    Hello all,

    So I was able to salvage my disc brake pads on my trek 3900 (at least the back ones for sure).

    I have a question about the front disc brakes. They do not lock up when I fully pull the lever. Is the normal. A guy at my LBS said that they should not lock up due to control reasons....and because going downhill and locking them up could prove a big bummer. Is this true?
    If you have enough stopping power to stop yourself within a reasonable distance, don't worry that you can't lock up your front brake. Your LBS is in fact correct in saying that it would be a huge bummer locking up the front wheel, since if the wheel is just skidding you have no control. If you stop the front wheel from spinning on a surface with more grip (rock/pavement/wood), your other option is to go flipping over the bike and faceplant.
    If it ain't broke, fix it 'till it is.

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