giskard

My new Kona Jake the Snake (2010 model) has some serious fork judder when braking at low speed. The Kore Race cantilever brakes have been adjusted by my LBS and were working fine, but a few days ago, whilst filtering through city traffic, I noticed serious judder and flex in the front (carbon) forks. Admittedly, I had an impending flat front tyre, could this be a factor?

What's the general fix for judder with canti brakes?

FastJake

Is the judder gone now that you fixed the flat?

On "road" bikes with more flexible forks, the usual cause of this is having the cable stop too far away from the straddle cable. Is your cable stop up on the headset? If so it can usually be moved down closer to the brake by using a mount that goes through the hole in the fork. I have never had this shudder problem on mountain bikes, even with very long main cables. Presumably the MTB forks are more rigid.

Also, if your brake pads are positioned poorly, it can sometimes cause squealing or other annoying stuff.

furballi

Clean the rims and pads with scotchbrite. Wipe with alcohol. Adjust pads so that they hit squarely on the rim. Some people prefer a 1mm toe-in at the front (1mm gap at the rear).

1saxman

This, plus possibly a need for adjusting the headset as well as a very close inspection of the rims to make sure there are no imperfections. You may simply have picked up some oil off the road that contaminated the braking surface.

1saxman

I don't like the word 'juddering', but will go ahead and use it as its too early for me to think of anything better - 'chattering' doesn't really work. In rebuilding my 1989 Bridgestone Comp MB2 that I bought new, but which was used hard by my son for a few years before limping home, I took a short ride before really starting work on it. When I applied the front brake, violent 'juddering' ensued. I had planned to replace the rims anyway, so I parked it and started working on it. When I went to put in the new Kool Stop brake pads, I realized that the RH cantilever arm on the front brake was twisted, resulting in pronounced 'toe-out' of that brake pad, or the rear of the pad contacting the rim first. Obviously this was the cause of the 'judder', but what happened to it? Then I remembered my son told me on the phone once that he had really crashed hard on a fast trail and badly warped the front wheel. He had the wheels trued. That's when it hit me - the badly warped rim slammed into the RH brake pad during the wreck, pulling it forward and twisting the arm. Fortunately, the new pads have a lot more adjustability than the old ones and I was able to get just a tiny bit of positive toe on that pad, so I expect it to be okay when I get the new wheels in. Its generally not a good idea to do any major twisting on aluminum components, but if I can't get it right during final assembly I will 'tweak' that arm with a large wrench.

Gerry Hull

Juddering perfect word. so what not in dictionary. I knew Exactly what you meant when I saw it. Can be caused by so many things.

I just bought some new Rolf Prima wheels. They have very atypical spoke set up. Design weakness in these wheels is that the rim is slightly flared at every spoke juncture. At the brake tracks the rim is, if you measure between the spokes, .740 wide. Measured at the spoke junctures, its .746-.748. Manufacturers instruction manual had said, You need to dial in a s-load of toe in with these wheels. When I read that I thought, hmm, wonder why? Then go ride it with brakes set flat on rim like usual. Judder my God. Tons of toe in alleviates symptoms but doesnt fix underlying problem. Trying to figure out how to fix it without destroying wheel.

But maybe you can narrow down problem by rotating wheel while applying light pressure to brake. See if it grabs at particular place or places.

tru

install one of these: https://www.specialized.com/us/en/bc/...jsp?spid=47409

1saxman

'Juddering' is a BS word and there are plenty of engineering terms existing to describe brake pulsation and cyclic 'grabbing'. Like many other new 'words', it only came into existance because of ignorance of the established terms describing the effect, which has been experienced since the invention of the wheel. I started seeing it on car forums referring to the same effect on brakes. I suppose the word came into being when somebody tried to describe a 'jarring shudder' and came up with 'judder'. Things like this remind me of a lady I used to work with from Alabama who had a delightful way of combining words into very descriptive non-words, like beaucoup and 'oodles' into 'beaucoodles', or 'flustered' and 'frustrated' into 'flustrated'. As cute as they may be, they're still not real words.
'But maybe you can narrow down problem by rotating wheel while applying light pressure to brake. See if it grabs at particular place or places.But maybe you can narrow down problem by rotating wheel while applying light pressure to brake. See if it grabs at particular place or places.

'But maybe you can narrow down problem by rotating wheel while applying light pressure to brake. See if it grabs at particular place or places.'

Like I said, I know what caused my problem, but that is obviously the first step in assessing the situation for anyone experiencing this.

'the rim is slightly flared at every spoke juncture.'

Wow - a brake chatter machine if I ever saw one. I'll bet it would take a ton of toe to stop that rim from chattering.

Jeff Wills

I had a couple bikes that would vibrate fiercely when I put the brake on. The thing they shared was new Velocity Aero rims and Kool-Stop salmon brake pads. Installing all-black pads cured the problem immediately, and once the rims had some miles on them the salmon pads worked fine, too.

I bet the OP's bike has some sort of rough finish on its new rims. A few wet rides will take care of that.

Hibonite

As others have stated it could be a number of things that all add up for fierce fork shudder. In my case it was that the CR720 brakes fit loosely on the pivots such that when the brake is applied the rotation of the wheel would twist the arms and the pads would end up being toe-out, despite having adjusted them toe-in at first. When i increased the toe in a lot, it fixed the problem for me.

giskard

It has a somewhat radially rough finish so I wouldn't expect that to cause problems, but I'm not discounting it as a possible cause.

s4442jlp

. . . you may find this of interest.

https://velonews.competitor.com/2010/...o-cross_101807

Most likely the simplest thing is to check that the front pads toe-in is exisiting; you can increase it to ~1.5mm and still maintain effective braking.

HillRider

Brake shudder is a real problem for road and cross bikes with cantilever brakes and particularly with carbon forks. The main cause seems to be the long span of brake cable between the headset mounted cable hanger and the brake itself. Here is Lennard Zinn's explanation of the cause and cure:

https://velonews.competitor.com/2010/...o-cross_101807

giskard

Thanks for all your feedback on this thread.

The brake shudder problem has now been fixed by my local repair shop - the fix was to replace the straddle cable and the lightweight alu hanger with a slightly heavier and far more solid steel hanger, the latter has made all the difference. Also the right-angled noodle was removed and the angle of the cable from the bars down into the cable housing is now gentler.

The attached pic shows the old cable setup at the bars but I'll post updated pics later today.

TurbineBlade

Yep, common problem. The fixes usually are:

1. toe in the brake pads
2. check the headset for play
3. install a fork crown housing stop

I did #3 because it had the added benefit of routing my brake cable a lot more smoothly. I had minor "judder" and it cured it instantly.

giskard

I did consider that because such a thing might also provide a cable adjuster but it would have meant more work that was required for the solution provided by my lbs.

cycle_maven

Just to be a nudge, the term "judder" is perfectly fine in this context. It describes the apparent "shudder" in the motion when 24 Hz film sources are shown on 50 or 60 Hz video displays. The rate of the motion artifact is approximately 10 Hz, so it's not that far a stretch to call any unpleasant 10 Hz mechanical motion that starts and stops "judder". BTW, "shudder" is something people do, not mechanical systems.

ecnewell 

I didn't think "judder" was a real word either, though I did understand what the OP meant. Turns out it's a perfectly cromulent word. I learned something today

From my MacBook's built-in dictionary:

jud•der |ˈjədər|
verb [ intrans. ] chiefly Brit.
(esp. of something mechanical) shake and vibrate rapidly and with force : the steering wheel juddered in his hand.

noun
an instance of rapid and forceful shaking and vibration : the car gave a judder.

joejack951

Possibly the strangest rant I've read in the mechanics forum. According to www.m-w.com "judder" has been in use since 1931. You probably have a better chance of causing the extinction of newer, not-real words like "email" and "cellphone" than something so entrenched in the English vocabulary as "judder".