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Old 09-03-11, 12:46 PM   #1
canflyboy 
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Front Fork Issue. Juddering under braking. Blue CXC

I picked up a Blue CXC fame and fork for my cross build. Full Carbon fork. Bike has shortish headtube. TRP brakes.

Just got the bike together and took it for a test ride. Whenever I hit the front brakes hard, the front tire judders. The tips of the fork actually oscilate back and forth quickly.

I haven't investigated further other that grabbing the front brake while sitting on the bike and rocking it back and forth. There sure seems to be a fair amount of "whip" at the tips of the fork. It doesn't appear to be any play in the headset.

Any ideas??


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Old 09-03-11, 01:25 PM   #2
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Your options are: lower the cable hanger(like a fork mounted hanger), switch to regular V-Brakes with a Travel Agent or mini V-brakes( TRP CX9, CX8.4) or switch to a stiffer fork(then you also have a disc brake as an option).
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Old 09-03-11, 04:20 PM   #3
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you need a brake cable hangar - either headset or fork mounted.
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Old 09-03-11, 05:20 PM   #4
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I have a brake cable hangar. It hangs from the head set. Went to a few LBS to find one that hangs lower, but no success. Going out to the garage to play with set up
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Old 09-03-11, 07:28 PM   #5
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LUCKY EASY FIX

So I went to the garage and install new brake pads. The TRP brakes were of another bike, but the pads were just broke in. Anyway, I put the new pads on, slight adjustment and viola - no more juddering.

Off to the races next week
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Old 09-03-11, 09:53 PM   #6
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On this topic... I don't know how long this link will point to the right story, but I couldn't find a permanent link. Anyway, a local company retrofitted a fork mounted cable hanger onto a fork with no hole. Check it out:

http://www.ruckuscomponents.com/blog
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Old 09-05-11, 01:23 PM   #7
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The fork mounted hanger thinggy you need is one of these;
http://www.rivbike.com/products/show/cable-hanger-frame-mount/15-089

They do make a huge difference reducing shudder.
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Old 09-05-11, 09:02 PM   #8
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The bottom line is cantilever brakes blow.
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Old 09-06-11, 10:48 AM   #9
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One way to keep canti brakes from chattering is to angle the brake pads with the end towards the rear touching the rim first. My Trek XO1 originally came with Avid Shorty 4's that always needed adjusted.
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Old 09-06-11, 11:32 AM   #10
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This is what you need and can order from Harris Cyclery, it's where I got mine:



It WILL solve your problem. It's actually a very common problem and is not due to low end brakes or cheap forks for that matter. But I'll let Leanord Zinn explain it to you in full detail:
http://velonews.competitor.com/2010/...shudder_147730
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Old 09-06-11, 04:52 PM   #11
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OK, I just don't get it. As far as I am concerned, shutter ought to be caused by the wheel prying itself free from the brake pad application. It is able to do this due to rotation about the fork blade axis, rotaing to the point that the pads loose grip, wheel breaks free, the cantilevers spring back, thus regaining grip, stopping the wheel again, then the process repeats. The issue then is rotation at the canti studs. The location of the brake cable stop is a non-sequitor as it only applys force in the verical direction through the brake cable, independent of the relative location of the cable stop. There are only two possible corrections. 1). Pads squishy enough to retain even pressure regardless of rotation, or 2).a bridge between the canti studs to provide torsional stiffness. If you have a cable stop that bridges between the studs, it is the bridging that stopped the shudder. I simply cannot see how a casble stop simply supported through a fork crown hole changes anything... Unless someone can explain what I am missing.
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Old 09-06-11, 05:42 PM   #12
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Originally Posted by balindamood View Post
OK, I just don't get it. As far as I am concerned, shutter ought to be caused by the wheel prying itself free from the brake pad application. It is able to do this due to rotation about the fork blade axis, rotaing to the point that the pads loose grip, wheel breaks free, the cantilevers spring back, thus regaining grip, stopping the wheel again, then the process repeats. The issue then is rotation at the canti studs. The location of the brake cable stop is a non-sequitor as it only applys force in the verical direction through the brake cable, independent of the relative location of the cable stop. There are only two possible corrections. 1). Pads squishy enough to retain even pressure regardless of rotation, or 2).a bridge between the canti studs to provide torsional stiffness. If you have a cable stop that bridges between the studs, it is the bridging that stopped the shudder. I simply cannot see how a casble stop simply supported through a fork crown hole changes anything... Unless someone can explain what I am missing.
http://velonews.competitor.com/2010/...o-cross_101807

Have a read^^^^ This explains why.
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Old 09-06-11, 05:48 PM   #13
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I've read it three times now. It does not make sense. The little diagram at the front of it only proves my point. Maybe I'm just dense.
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Old 09-07-11, 01:22 PM   #14
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Originally Posted by balindamood View Post
I've read it three times now. It does not make sense. The little diagram at the front of it only proves my point. Maybe I'm just dense.
Let's try for the simply explanation.

The user applies brakes, inertia causes fork to bend back, this causes the tension on the cable to increase (pythagorean theorum), the fork rebounds, and the cable tension relaxes, the brakes catch the wheel again, causing the cycle to continue.

The culprit is the flex in the system between where the cable stop is mounted and the brakes themselves. Less flex in this area means less change in cable tension, and less of the feedback that causes the cycle.
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Old 09-07-11, 03:56 PM   #15
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Perhaps I have a bit more length in all of my straddle wires, but the difference in length between the brakes on, and the brakes on with the fork sprung back is infitessimally small. Even so, the result would be the brakes being applied harder, further preventing the wheel from being released. Either the rider goes up and over, or the wheel breaks free from the ground. Cable tension is not a function of cable housing length (practically speaking); the tension in the cable is the same outside the housing as in, regardless of housing length. If it is a function of cable stop flex as you suggest, then a better headset-mounted cable hander would be all that is required.

I further point to the discussion in the canti-brake sticky where it points out that Richard Sach's team has been spotted with unusually short (i.e., cut/shortened), brake pads...presumably to reduced shudder. This would seem to support my prying position over the cable tension because there is less of a lever arm for the wheel to pry the pads.

I am not trying to be an @ss. I have some minor shutter issues, and no fork crown hole for a different cable hanger. As information, I did try a Delta Brakebrace on it (no cable hanger change) and did not see much, if any, of an improvement, though as the pads are wearing in (and the last remnents of a sloppy tire gluing job fade), the shutter is almost gone. I switched from the Ritchey (Kool Stop) big pads which were really bad, to non-pedigreed jagwire pads which seemed to make the biggest improvement. If it does not completely go, I am going to cut the long ends off the pads and see if that helps.
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Old 05-18-12, 12:53 PM   #16
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I first tried using the generic tektro aluminum bolt-on hanger but on my fork, the hanger did not have sufficient clearance to get around the lower portion of the headset without adding a substantial stack of spacers. The cast aluminum hanger also really didnt fit with aestheics of the handbuild steel bike. Inspired by this great thread over in the v-salon framebuilders forum;
http://www.velocipedesalon.com/forum...ops-24841.html
I decided to try fabricating my own fork mounted cable stop for the steel CX fork & frame that I built. (a few pictures if rest of the frame here if interested https://picasaweb.google.com/1102452...eat=directlink .)
I had minimal success with bending tubing like the Shamrock example in above thread (the tubing would kink), decided to build it using tubular steel design that is a bit more inspired by Tom Kellogs/spectrum design in above thread.







For materials, I cheated and started with an old roadbike seatstay with a nice classy looking capped end which I scavenged from an damaged frame. I cut an angled miter in the tube at 35°, so than when the two pieces were flipped and then pieced back together, it angled outward by 20° and the forward facing flat cap of the old seatstay was parallel to the steertube. I sized the length of the shorter piece of tube so that the longer angled cap piece would just clear the headset, avoided the more elaborate clearance notch that spectrum used. Once the two mitered pieces were lightly tacked together, I took another piece from the smaller end of the seatstay that can fit inside the short larger diameter tubing, gave the smaller diameter tube a miter angle around 45° on one end (so it overhangs a bit on the top end of the miter) and then inserted it into the short spacer sleeve and brazed it all together. The smaller diameter inner tube helps to firmly support the longer angled piece. I drilled the crown for the smaller inner tube to pass through the front and will braze it in-place at the inside/back of the crown and at the hole in the front of the crown, the short piece of outer tubing will also get a small fillet of exterior braze and should make for a nice stiff and strong assembly. The cable stop barrel is brazed onto the front of the seatstay cap and is threaded to allow for minor cable tension adjustment using an adjuster barrel scavenged from an old road brakeset.

End result weights 43gr, just a bit more than the 37gr tektro aluminum bolt-on version
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Old 05-20-12, 02:53 PM   #17
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Now that is cool.
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Old 05-23-12, 03:10 PM   #18
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I had an uncontrollable shudder issue w/my Felt F1X CX and carbon fork w/canti. The fork had an unrelated defect from the mfctr, replaced, same problem. No amount of adjusting made a difference.

Replaced the canti with a mini-V, problem solved. $20.
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Old 05-27-12, 06:47 AM   #19
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It would have been nice if some one had remembered we have the stickied canti faq just for this sort of thing!
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