Solving front fork judder.

Marcus_C

A colleague of mine has tentatively started commuting to work on his hybrid, not a bad one as far as they go, however, he's been complaining about fork judder under braking, I had a quick ride this lunchtime and, holey moley it's bad!! I presume the basic problem is the alloy fork but is there anything apart from a new fork that would help? Different brakes etc? He's getting a new stem to replace the adjustable one which creaks rather badly but I can't think that'd be the problem.

I've never had much of a fork judder problem so i'm a bit lost what to suggest.

shefbiker

Where is the movement happening? headset? wheel/hub? hub/fork?

does it only happen during braking?

shefbiker

oh, and what brakes? v-brakes? or disk? cable or hydraulic?

Marcus_C

It's in the fork, only during braking and they're tektro v-brakes.

[Tim]

http://velonews.competitor.com/2010/09/ ... oss_101807

Uphanger?

desweller

I would make my way through this list:

Make sure there's no play in the hub.
Check that the front wheel is true, that there's no damage on the rim and that it's properly fitted to the fork.
Clean both the rim and brake block surfaces.
Make sure there's no excessive play in the brake arms.
Remove the brakes and check that they are not cracked or otherwise structurally damaged. If they're OK, clean (i.e. with wire wool) and regrease the pivots before refitting.
Make sure the brake blocks are mounted square or slightly toed in to the rim.

Marcus_C

Will do that, he cycled in today again, thanks for the tips.

The Rookie

One option is to slightly overtighten the headset and see if this removes the judder quick trial) and then set it back.

I would suspect loose/worn brake pivots, some toe in (actually its toe out, but you look at it the 'wrong way' and everyone calls it toe in now) on the pads will often sort this for a while anyway.

Ignore the bit in tims link about the uphanger (bow string) as that is specific to stone age canti's, not V's.

Simon

Blue Meanie

Cheap forks can have non-parrell bosses. Remove the canti arms and insert long bolts (to exaggarate the effect) and measure with vernier calipers. If they are off, it's new fork time, or just put up with it

AndyOgy

Blue Meanie wrote:

Cheap forks can have non-parrell bosses. Remove the canti arms and insert long bolts (to exaggarate the effect) and measure with vernier calipers. If they are off, it's new fork time, or just put up with it

Even expensive forks suffer from this. That's why V-brake pads come with 2 sizes of concave washer, so that you can flip these around to overcome the problem. I have never seen a set of Kona P2's, for example, where the brake bosses are parallel.

The P2's fitted to one of my bikes has brake bosses which are out by quite a bit. Even if I install V-brakes without flipping the washers, the braking power is still unaffected (ie, no judder), they just look a bit odd.

Does the bike in question have suspension? If so, apply the front brake and gently rock the bike forwards. Watch the bridge of the fork and see if it moves independently (back and forth) of the fork uppers. There is often some play here, which causes fork judder. Best solution is some very extreme toe-in on the front brake pads.

The Rookie

AndyOgy wrote:

Blue Meanie wrote:

I have never seen a set of Kona P2's, for example, where the brake bosses are parallel.

From an engineering viewpoint I doubt any forks have truly parallel bosses if you make accurate enough measurements! The importance really is the degree of out of parrallel and how well the pad is set to accomodate the discrepancy(ies).

Simon