Advertise on Bikeforums.net



User Tag List

Results 1 to 20 of 20
  1. #1
    Senior Member
    Join Date
    Jan 2012
    Location
    Spokane, WA
    My Bikes
    Specialized Sequoia Elite/Motobecane Fantom Cross Team Ti/'85 Trek 520
    Posts
    2,227
    Mentioned
    4 Post(s)
    Tagged
    0 Thread(s)

    Why are my brakes so mushy? STI brifters with 105 caliper and Dia-compe caliper

    I built a bike up from spare parts a few ebay parts. The shifters are 7 speed RX100/105 pair. They were purchased separately hence the rx100 on the left and the 105 on the right. The rx100 left shifter is a double. The 105 right shifter is a 7 speed. The front caliper is a Dia-compe single pivot and the rear caliper is a Shimano 105 dual pivot. I could not use my matching 105 front caliper because the reach of it was too short by about 4-5mm so I had to dig in my bike coop for a workable front brake and found the nice Dia-compe single pivot. It is styled like the newer brakes so its fairly recent.

    When the brakes are squeezed, you can touch the handlebars with the tips of the brake levers. They feel almost squishy once they start to hit the wheel.

    I'm used to setting up v-brakes and cantilevers, this is my first road bike style brakes.

    I put all new housings in place, just standard spiral housing. I adjusted the pad distance to be a tad forgiving but I didn't think that would be a big deal but apparently it might be. Am I supposed to be adjusting the pads so they barely are touching when the brakes aren't being used? Am I missing something?

  2. #2
    Senior Member IthaDan's Avatar
    Join Date
    Jan 2012
    Location
    Ithaca, NY
    My Bikes
    Click on the #YOLO
    Posts
    4,627
    Mentioned
    7 Post(s)
    Tagged
    0 Thread(s)
    What kind of pads are you running? How firmly seated was the housing in the lever before you wrapped the bars?

    Shimano : Click :: Campy :: Snap :: SRAM : Bang

  3. #3
    Senior Member
    Join Date
    Jan 2012
    Location
    Spokane, WA
    My Bikes
    Specialized Sequoia Elite/Motobecane Fantom Cross Team Ti/'85 Trek 520
    Posts
    2,227
    Mentioned
    4 Post(s)
    Tagged
    0 Thread(s)
    I haven't wrapped the bars yet. I'm waiting until I get everything all tuned up and working properly, then i will wrap the bars. At this point, I'm kind of glad i didn't. LOL The cables are running along the groove in the drop bars and covered in electrical tape until everything is working well.

    The cables are fully seated as far as I can tell. I squeeze the handle and see the little cable stop is firmly in the recess on both levers. When I put the ferrules on the housings, I tapped them on lightly using a small hammer to make sure they were fully seated. The closest analogy I can come to is that the brakes feel like I'm using a cantilever brake lever (long pull) with v-brakes (short pull).

    Is it possible that I have the brifter too low on the curve of the drop bar so that the pull of the lever isn't enough?

    Unknown pads but they look like new and are pliable, not dry rotted or brittle.

  4. #4
    coprolite fietsbob's Avatar
    Join Date
    Jun 2010
    Location
    NW,Oregon Coast
    My Bikes
    7
    Posts
    39,118
    Mentioned
    20 Post(s)
    Tagged
    0 Thread(s)
    Aero brake-levers and road brifters have a high MA, that leverage
    is probably what you feel as Mushy.
    tighten up the rim to pad clearance adjustment, so little lever pull is devoted
    to just moving the pad to the rim, and you will stop fine.
    Kool Stop brake pads ..
    Last edited by fietsbob; 05-21-12 at 02:40 PM.

  5. #5
    Senior Member
    Join Date
    Jan 2012
    Location
    Spokane, WA
    My Bikes
    Specialized Sequoia Elite/Motobecane Fantom Cross Team Ti/'85 Trek 520
    Posts
    2,227
    Mentioned
    4 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by fietsbob View Post
    Aero brake-levers and road brifters have a high MA, that leverage
    is probably what you feel as Mushy.
    tighten up the rim to pad clearance adjustment, so little lever pull is devoted
    to just moving the pad to the rim, and you will stop fine.
    Kool Stop brake pads ..
    I will do that. Tighten up the clearence and get some new pads, I bet my LBS has some kool stop pads. Good ideas.

    I'm just not used to these brakes, never had aero brake levers before and have never touched a set before on a bike. LOL

  6. #6
    Senior Member
    Join Date
    Sep 2010
    Posts
    2,591
    Mentioned
    1 Post(s)
    Tagged
    0 Thread(s)
    The question is, do the brakes stop the bike effectively? Hard-feeling brake levers do not equal effective brakes, less-firm are not necessarily poor performers. Also be certain that the cable housings were cut squarely and filed flat before the ferrules were put on. Excessive pad toe-in or pads not squarely aligned with the wheels' brake tracks will also contribute to a less-than-firm feel.

  7. #7
    Senior Member IthaDan's Avatar
    Join Date
    Jan 2012
    Location
    Ithaca, NY
    My Bikes
    Click on the #YOLO
    Posts
    4,627
    Mentioned
    7 Post(s)
    Tagged
    0 Thread(s)
    How much are the housings moving around when you hit the brakes? Any movement is robbing the effort at the lever from clamping the pads. Obviously some of it will happen no matter what you do, but it might give a different lens to look for a problem.

    Shimano : Click :: Campy :: Snap :: SRAM : Bang

  8. #8
    Senior Member
    Join Date
    Jan 2012
    Location
    Spokane, WA
    My Bikes
    Specialized Sequoia Elite/Motobecane Fantom Cross Team Ti/'85 Trek 520
    Posts
    2,227
    Mentioned
    4 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by dsbrantjr View Post
    The question is, do the brakes stop the bike effectively? Hard-feeling brake levers do not equal effective brakes, less-firm are not necessarily poor performers. Also be certain that the cable housings were cut squarely and filed flat before the ferrules were put on. Excessive pad toe-in or pads not squarely aligned with the wheels' brake tracks will also contribute to a less-than-firm feel.
    The housings were cut squarely and filed flat. The pads don't appear to have adjustable toe-in on the calipers I used. As for stopping, the reason why I posted this was because my son who test drove the bike yesterday said that it wasn't stopping well when he hit the brakes. he said he was squeezing it to the handlebar and it wasn't stopping like it should.

    Quote Originally Posted by IthaDan View Post
    How much are the housings moving around when you hit the brakes? Any movement is robbing the effort at the lever from clamping the pads. Obviously some of it will happen no matter what you do, but it might give a different lens to look for a problem.
    I will look at the housing and see how much they are moving when the levers are squeezed when i get home.

  9. #9
    Constant tinkerer FastJake's Avatar
    Join Date
    May 2010
    Location
    Madison, Wisconsin
    Posts
    6,120
    Mentioned
    1 Post(s)
    Tagged
    0 Thread(s)
    +1 to everything. Get the pads as close to the rim as possible, and make sure the housing is fully seated in the brake levers. It can be tricky to get it jammed all the way in some of those aero levers. You could also just have a brake mechanical-advantage mismatch with that Dia-Compe brake.

    I found when using Shimano aero levers and some really old trashed Mafac centerpulls they were really mushy and I could almost bottom out the levers if I pulled hard enough. Now with bullhorns and 'cross interrupter levers, I can easily throw myself over the bars.

    Quote Originally Posted by dsbrantjr View Post
    The question is, do the brakes stop the bike effectively? Hard-feeling brake levers do not equal effective brakes, less-firm are not necessarily poor performers.
    True, but if the levers can bottom out on the handlebars something is definitely wrong.
    Why "derailer" is the correct way to spell the gear-change mechanism: sheldonbrown.com/derailer.html

  10. #10
    Senior Member
    Join Date
    Jan 2012
    Location
    Spokane, WA
    My Bikes
    Specialized Sequoia Elite/Motobecane Fantom Cross Team Ti/'85 Trek 520
    Posts
    2,227
    Mentioned
    4 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by FastJake View Post
    +1 to everything. Get the pads as close to the rim as possible, and make sure the housing is fully seated in the brake levers. It can be tricky to get it jammed all the way in some of those aero levers. You could also just have a brake mechanical-advantage mismatch with that Dia-Compe brake.
    Well I double checked everything and adjusted things some more. The front brake feels much better oddly enough (that is the older dia-compe single pivot) but the rear still feels a bit mushy, if I pull hard, I can pull it to the bar.

    However I did notice that the front housing does distort when I pull the brakes hard. Kind of like it is taking up slack that should not be present. So tonight I'm going to remove that housing and put a new one in its place and see if that helps. I might also shorten the housing up the new housing as well. But there is certainly a shortening of the housing when the brake is pulled.

    As for why I can't test it myself, I broke my leg a couple months ago and also badly sprained my ankle. My ankle is still a big problem.

  11. #11
    Senior Member mechBgon's Avatar
    Join Date
    Jul 2002
    Posts
    6,957
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    With Shimano levers, don't use ferrules. They take the housing as-is.

  12. #12
    Collector of Useless Info
    Join Date
    Aug 2009
    Posts
    1,287
    Mentioned
    4 Post(s)
    Tagged
    0 Thread(s)
    Does the rear brake housing run all the way from the lever to the brake? If so, then the housing compression will definitely make the rear brake feel spongier than the front. That's why modern bikes have a couple of cable stops on the top tube- the top tube is pretty incompressible. Nuthin' you can do about that, except braze on a couple of stops... Fortunately, 70% or more of your stopping power is in the front brake.

    Also, older single-pivot dia-compe's are going to flex more than the dual-pivot 105's. I'd make a drop-bolt for the 105 front brake IIWY.

  13. #13
    Senior Member
    Join Date
    Jan 2012
    Location
    Spokane, WA
    My Bikes
    Specialized Sequoia Elite/Motobecane Fantom Cross Team Ti/'85 Trek 520
    Posts
    2,227
    Mentioned
    4 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by mechBgon View Post
    With Shimano levers, don't use ferrules. They take the housing as-is.
    Got it, thanks. Ferrule at the cable stop end, no ferrule at the lever end, correct?
    Quote Originally Posted by cycle_maven View Post
    Does the rear brake housing run all the way from the lever to the brake? If so, then the housing compression will definitely make the rear brake feel spongier than the front. That's why modern bikes have a couple of cable stops on the top tube- the top tube is pretty incompressible. Nuthin' you can do about that, except braze on a couple of stops... Fortunately, 70% or more of your stopping power is in the front brake.

    Also, older single-pivot dia-compe's are going to flex more than the dual-pivot 105's. I'd make a drop-bolt for the 105 front brake IIWY.
    I was thinking about doing something like that. The Dia-compe is just a stop gap measure until I get something better in its place.

  14. #14
    coprolite fietsbob's Avatar
    Join Date
    Jun 2010
    Location
    NW,Oregon Coast
    My Bikes
    7
    Posts
    39,118
    Mentioned
    20 Post(s)
    Tagged
    0 Thread(s)
    I'd guess the added MA of the dual pivot brake + longer cable and housing add up.

    NB the newer Campag race Groups, the single pivot is in the back,
    dual pivot on the front.
    just the opposite... all the work stopping takes place up front,
    and the rear wheel is getting unweighted.
    + that caliper is able to be made lighter.

  15. #15
    Senior Member mechBgon's Avatar
    Join Date
    Jul 2002
    Posts
    6,957
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Got it, thanks. Ferrule at the cable stop end, no ferrule at the lever end, correct?
    If the cable stops or adjusting barrels will accept a ferrule, then use one in those places, yeah.

  16. #16
    bike whisperer Kimmo's Avatar
    Join Date
    Dec 2009
    Location
    Melbourne, Oz
    My Bikes
    copy/paste links: http://velospace.org/node/36949 http://velospace.org/node/47746 http://velospace.org/node/47747
    Posts
    6,828
    Mentioned
    7 Post(s)
    Tagged
    0 Thread(s)
    This makes me cringe... having a DP on the front and a SP on the rear is perfect, but vice versa is awful.

    I'd change the fork so I could run the DP.

  17. #17
    Retro Grouch onespeedbiker's Avatar
    Join Date
    Oct 2007
    Location
    Santa Cruz
    My Bikes
    Yes
    Posts
    2,001
    Mentioned
    1 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by cycle_maven View Post
    Does the rear brake housing run all the way from the lever to the brake? If so, then the housing compression will definitely make the rear brake feel spongier than the front. That's why modern bikes have a couple of cable stops on the top tube- the top tube is pretty incompressible. Nuthin' you can do about that, except braze on a couple of stops...
    Not exactly true, assuming the OP's bike has a round top tube there is the clamp on variety. http://www.amazon.com/Origin8-Clamp-.../dp/B003BCCAFM

  18. #18
    Collector of Useless Info
    Join Date
    Aug 2009
    Posts
    1,287
    Mentioned
    4 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by onespeedbiker View Post
    Not exactly true, assuming the OP's bike has a round top tube there is the clamp on variety. http://www.amazon.com/Origin8-Clamp-.../dp/B003BCCAFM
    True dat. I really didn't want to suggest something like this for brakes, though. Gears, fine. There's an enormous amount of force on the cable when braking hard and I'd be worried about the cable stop slipping at the worst possible time- when you squeeze the brake levers the hardest is when you need them the most. OTH, the rear brake isn't all that critical in a panic-stop- the rear wheel lifts off making the rear brake ineffectual, so it's probably fine.

  19. #19
    Senior Member
    Join Date
    Apr 2011
    Location
    Baltimore, MD
    My Bikes
    2010 GT Tachyon 3.0
    Posts
    1,192
    Mentioned
    3 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by cycle_maven View Post
    OTH, the rear brake isn't all that critical in a panic-stop- the rear wheel lifts off making the rear brake ineffectual, so it's probably fine.
    Flame war time. Every time you mention the rear brake doesn't work, people will flame-war you. Mind you I've skid front tires on bikes and made the bikes go down that way; but people are convinced that you can't hold the bike down and will endo if you use your front brake. (I've endo'd off the rear brake, too...)

    My folding bike has an excessive amount of housing methinks, along with poor cable routing. The rear brake doesn't do anything.
    Own: 2010 GT Tachyon 3.0
    Own: 2013 Trek Domane 2.0 + Revolution REV22 wheels

  20. #20
    Constant tinkerer FastJake's Avatar
    Join Date
    May 2010
    Location
    Madison, Wisconsin
    Posts
    6,120
    Mentioned
    1 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by bluefoxicy View Post
    Flame war time. Every time you mention the rear brake doesn't work, people will flame-war you. Mind you I've skid front tires on bikes and made the bikes go down that way; but people are convinced that you can't hold the bike down and will endo if you use your front brake. (I've endo'd off the rear brake, too...)
    Going backwards? Because it's not possible to endo while going forwards and only applying the rear brake.

    I don't see how this is a flame war topic, it's simple physics really.
    Why "derailer" is the correct way to spell the gear-change mechanism: sheldonbrown.com/derailer.html

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •