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  1. #1
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    Front end wobble under braking?

    Just built up my first 29er and took it for a trail ride, I haven't been able to go over it to check for anything that may have loosened but yet.

    What I'm noticing is under braking is the fork wobbling/vibrating front to back. I'm running Mavic C29ssmax wheels and hubs, Avid BB7's with 160mm rotors, RS Reba 2010 fork. The for was aired up to my weight just prior to the ride as were the tires so I had proper pressure(s). I know the rotor was tight to the rim but it could have come loose during the ride.

    What should I check tonight?

  2. #2
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    Make sure you preloaded the stem
    Loosen stem - torque topcap to headset specs (or what feels good without binding) and tighten stem back

  3. #3
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    Quote Originally Posted by ShadowFox1290 View Post
    Make sure you preloaded the stem
    Loosen stem - torque topcap to headset specs (or what feels good without binding) and tighten stem back
    That's the first thing to check . . . the next thing would be the fork bushings. My fork does the same thing . .

  4. #4
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    Quote Originally Posted by ShadowFox1290 View Post
    Make sure you preloaded the stem
    Loosen stem - torque topcap to headset specs (or what feels good without binding) and tighten stem back
    When you say 'preload the stem' is that different than just tightening it? I don't have a torque wrench so I never know how hard to crank down on it. It is a brand new headset but the fork/wheel/brake are all used for what that matters.

  5. #5
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    I may have a similar problem although I wouldn't quite call it a wobble. I never had the problem with v-brakes but I recently switched to disc. The headset and all brake mounts/disc are torqued and have no noticeable slop, but under hard braking it chatters quite noticeably. My only guess is it's vibrations due to wear in the fork.

  6. #6
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    Quote Originally Posted by RCook View Post
    When you say 'preload the stem' is that different than just tightening it? I don't have a torque wrench so I never know how hard to crank down on it. It is a brand new headset but the fork/wheel/brake are all used for what that matters.
    The stem bolts merely attach the stem to the steerer. The headset bearing load is what is adjusted with the top cap/bolt (this adjustment must be done without the stem bolts tight). The preload determines how much force is exerted on the bearings to keep the steerer tube/fork in place and able to turn smoothly. Its a fine line....too little and there is slop or shudder....too much and the bind between bearings and race will drag when trying to steer.
    You need to tighten to a certain point then check that there is no slop in the steerer (turning the bars to 90deg then rocking back and forward will isolate the headset slop from any brake/fork bushing slop present) and also simultaneously make sure the steering is still free of drag.
    Rimmer - "There's an old human saying - if you talk garbage, expect pain"

  7. #7
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    Quote Originally Posted by AlexRandall View Post
    The stem bolts merely attach the stem to the steerer. The headset bearing load is what is adjusted with the top cap/bolt (this adjustment must be done without the stem bolts tight). The preload determines how much force is exerted on the bearings to keep the steerer tube/fork in place and able to turn smoothly. Its a fine line....too little and there is slop or shudder....too much and the bind between bearings and race will drag when trying to steer.
    You need to tighten to a certain point then check that there is no slop in the steerer (turning the bars to 90deg then rocking back and forward will isolate the headset slop from any brake/fork bushing slop present) and also simultaneously make sure the steering is still free of drag.
    Thank you, that explains in very well. I'm almost certain that I didn't torque the topcap nut enough for fear of binding the bearings. I'll tighten properly and I'm sure this will fix it.

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    Quote Originally Posted by RCook View Post
    Thank you, that explains in very well. I'm almost certain that I didn't torque the topcap nut enough for fear of binding the bearings. I'll tighten properly and I'm sure this will fix it.
    When free the hadlebars should easily return to center...

  9. #9
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    Quote Originally Posted by jeffscott View Post
    When free the hadlebars should easily return to center...
    You mean while a bike is in the stand I assume? Level or angled downward?

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    Quote Originally Posted by OO7 View Post
    You mean while a bike is in the stand I assume? Level or angled downward?
    Yup, normal stand postion front end down a bit.

  11. #11
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    Bushes make the fork stop working for small hits and become all sticky you'd notice that.

  12. #12
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    Quote Originally Posted by RCook View Post
    Thank you, that explains in very well. I'm almost certain that I didn't torque the topcap nut enough for fear of binding the bearings. I'll tighten properly and I'm sure this will fix it.
    Scroll down to...Headset Adjustment - Threadless Type.

    Can we assume that you installed the crown race that came with the new headset onto the fork?

  13. #13
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    Yes race installed.

    I tightened the headset as explained and all braking problems went away! Thanks for the help everyone!

  14. #14
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    Try cleaning your rotors. I had the same issue on the front of my disc brake cross bike (front fork shutter) running BB7s and had to make sure the rotors were really clean.

  15. #15
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    I recently noticed this with my current bike set-up.

    I ran a Fox RLC 100 for Tour Divide, then stuck that fork on my Santa Cruz Superlight 650b set-up. I am running XT hydros and Alligator rotors. Headset/stem is tight, calipers tight, but still get that odd vibration while braking.

    Going to look it over again soon.

  16. #16
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    Quote Originally Posted by FNFAL View Post
    I recently noticed this with my current bike set-up.

    I ran a Fox RLC 100 for Tour Divide, then stuck that fork on my Santa Cruz Superlight 650b set-up. I am running XT hydros and Alligator rotors. Headset/stem is tight, calipers tight, but still get that odd vibration while braking.

    Going to look it over again soon.
    Well considering the fact that your fork has 2700 MILES ON IT ALREADY (), I would check the bushing's in the lowers . . . that'd be the first place I'd look. Worn bushing's will create fore-aft play between the uppers and lowers that will become quite noticeable as the brakes are applied. I'd give some serious though to just rebuilding the whole thing to be honest . . .

    While on the TD did you notice this issue? What if you put the fork back on the Sette? Does it still do it?

  17. #17
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    Quote Originally Posted by OO7 View Post
    Well considering the fact that your fork has 2700 MILES ON IT ALREADY (), I would check the bushing's in the lowers . . . that'd be the first place I'd look. Worn bushing's will create fore-aft play between the uppers and lowers that will become quite noticeable as the brakes are applied. I'd give some serious though to just rebuilding the whole thing to be honest . . .

    While on the TD did you notice this issue? What if you put the fork back on the Sette? Does it still do it?
    No, never noticed it while on the tour. I DID notice however that my rear brake for the tour (Avid Elixer CR) would rattle the bike big time. That was the only brake problem I had, other than bent rotors.

    Don't have the Sette frame anymore. Sold it! I was thinking that it might be the bushings being worn. That's unfortunate, since I don't really have the money to fix that at this moment.

    Oh well, it'll ride for now. And it's not too terribly noticeable.

  18. #18
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    Pretty sure its a cheap/easy fix . . . take the lowers off, pop out the old bushings, put in the new ones (which are ~$25 for a set online) and reassemble with proper fluid levels. Should be able to do the whole thing in under an hour (give or take a few depending on how many beers you drink).

  19. #19
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    I found this thread looking for my problem:

    I have a GT Grade road bike with disc brakes. The wheel is true, the headset correctly tightened (as far as I can tell).

    When I break lightly, I feel some kind of rhythmic feedback on the lever. When I brake heavier, I see the front wheel wobbling laterally. I don't think I feel the whole front end of the bike wobbling, just the wheel.

    I looked on the disc and tried to find out if it is bent (with a metal workshop ruler). Seems to be true also. I already unscrewed and adjusted the rotor several times (screwing while breaking). That last corrective action seems to have some kind of impact, sometimes it got worse, sometimes better. But the wobble is still there.

    Is this a typical thing for disc road bikes? Its one year old, about 3.000 km on it.

    Thanks for your thoughts!

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