Results 1 to 11 of 11
  1. #1
    mtbr member
    Reputation: carpio77b's Avatar
    Join Date
    Sep 2011
    Posts
    70

    203mm shimano rotor - no modulation

    I just installed a 203mm rotor Shimano RT78 on my Pivot Mach 5 on a reccommendation from a riding buddy - we ride in Socal where there are alot of steep downhills. I am a trail rider, and am 6'2" 185# geared up. When I purchased the bike second hand, it had a 180mm rotor on the rear and a 160mm on the front. This didn't seem to make sense, as most of the stopping power comes from the front brake. Anyway, rode today with the 203mm for the first time (I also changed both front and rear pads
    from resin to sintered metal pads) and I had an endo in a tight corner, that also pitches down into the turn followed by upward pitch out of the turn. I blame the endo on the fact that the 203mm has basically no modulation - it's either on or off. The force of the endo was so great that the tube literally ballooned out from under the wheel

    Anyways, do any of you guys running a 203mm rotor find that there is no modulation or is this something I can adjust? Also, could the brand new pads play a part in the on/off front brake problem I am having?

  2. #2
    mtbr member
    Reputation:
    Join Date
    Oct 2009
    Posts
    222
    Bigger rotor - less modulation.

  3. #3
    LightJunction.com
    Reputation: lightjunction's Avatar
    Join Date
    May 2011
    Posts
    774
    Quote Originally Posted by vanamees View Post
    Bigger rotor - less modulation.
    Exactly. Can always try switching to a 185 or something. Maybe even adjust your pad contact so your brakes aren't so touchy, but a nicer brake is the best way to get better modulation.
    We sell quality bike headlights and flashlights.
    www.LightJunction.com

  4. #4
    mtbr member
    Reputation:
    Join Date
    Dec 2006
    Posts
    1,253
    what brakes? I absolutely love my Saints with 8" rotors, plenty of control, it does take some getting used to though, hafta use a light touch.
    '14 rocky mountain altitude, rally edition
    '11 transition blindside

  5. #5
    mtbr member
    Reputation: gticlay's Avatar
    Join Date
    Dec 2007
    Posts
    6,571
    You didn't say what brakes, but I run 203mm with Saints on both my trailbikes and it's a great setup. Sometimes I wish for more power with less pull. Anyway, I've noticed that the resin is weaker overall and modulates better while the sintered have a ton of power but are a little more grabby. So you might want to go back to resin and send me your sintered
    "It looks flexy"

  6. #6
    mtbr member
    Reputation: carpio77b's Avatar
    Join Date
    Sep 2011
    Posts
    70
    My brakes are XT M775 levers and calipers. I like to have a little free play on the lever before the brakes lock up. The "free play" screw on the lever doesn't seem to do anything and the pistons on the caliper are backed in as much as possible so would the solution be to remove a little bit of fluid from the release valve on the caliper?

    Maybe even adjust your pad contact so your brakes aren't so touchy

    What do you mean by adjusting the pad contact?

  7. #7
    mtbr member
    Reputation: gticlay's Avatar
    Join Date
    Dec 2007
    Posts
    6,571
    There's a freeplay screw on the lever body - little phillips on top.
    "It looks flexy"

  8. #8
    mtbr member
    Reputation:
    Join Date
    May 2007
    Posts
    161
    Quote Originally Posted by vanamees View Post
    Bigger rotor - less modulation.
    Sorry...bigger rotor means increased modulation.

    As for the OP, I noticed when I changed my last set of pads, as soon as they started to break in, they had ZERO modulation; they were either on or off. The next ride, the pads broke in a little more, and the modulation had greatly increased. I would say, give the bikes another ride, and see what happens. They should be better.

  9. #9
    mtbr member
    Reputation: carpio77b's Avatar
    Join Date
    Sep 2011
    Posts
    70
    Quote Originally Posted by project_d View Post
    Sorry...bigger rotor means increased modulation.

    As for the OP, I noticed when I changed my last set of pads, as soon as they started to break in, they had ZERO modulation; they were either on or off. The next ride, the pads broke in a little more, and the modulation had greatly increased. I would say, give the bikes another ride, and see what happens. They should be better.
    I bled out a very small amount of oil from the caliper by squeezing the lever with the bleed valve open. Made sure to keep the lever depressed while shutting the bleed valve to prevent the introduction of air. Now the modulation feels alot better, though I have yet to get out on the trail.

    As the pad wears, do the pistons reposition to keep free play and modulation similar or will I need to add mineral oil?

  10. #10
    mtbr member
    Reputation: gticlay's Avatar
    Join Date
    Dec 2007
    Posts
    6,571
    Quote Originally Posted by carpio77b View Post
    I bled out a very small amount of oil from the caliper by squeezing the lever with the bleed valve open. Made sure to keep the lever depressed while shutting the bleed valve to prevent the introduction of air. Now the modulation feels alot better, though I have yet to get out on the trail.

    As the pad wears, do the pistons reposition to keep free play and modulation similar or will I need to add mineral oil?
    They reposition pretty well, I think because of the rubber bladder in the lever. Every once in a while you need to clean the pistons and relube with mineral oil. I love them, but Shimano brakes need that way more than other brands.
    "It looks flexy"

  11. #11
    Commit or eat sh!t
    Reputation: Cable0guy's Avatar
    Join Date
    Jun 2007
    Posts
    2,368
    I found the XT M775 brakes to be either on/off, with very little modulation, especially with metallic pads. You should try the newer 2012 XT's (M785), or Formula brakes as a comparison. Much better.

Posting Permissions

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