[jeff]

I feel like this has been addressed before but I couldn't find the thread (or maybe it was one of Syd's blog posts). Anyway, I just started noticing my fork stutters rapidly when I apply my front brakes and it's most noticeable on pavement. I tried adjusting the rebound settings thinking the fork was to blame but that didn't do it. Now I'm thinking it's the brakes... I did replace the pads in the last couple of months but didn't notice anything until now. Ideas?

[mtbgreg1 offline]

Rebound settings would have been my guess, but I'm no syd. How's your air pressure in the fork? Did you check to make sure it's aired up all the way?

[GoldenGoose]

Is the fork diving a bit on braking or, by "stuttering", do you mean you are feeling a pulsing type feeling as you brake? Two different causes.

Pulsing is usually a rotor/pad interface type issue. Sometimes rotors and brake calipers dont play nice and you get this issue. I've had rotors with large ventilation holes will make this pulsing feel. I've been able to recenter the caliper to fix the issue and I've also heard of people using a thin shim to move the entire caliper out which also helped.

Fork dive upon braking is usually a sign of too little air pressure or a spring that isn't firm enough for your weight.

[jeff]

It's definitely not diving. If anything the pressure is too high in the fork (not getting the full travel).

Riding on flat pavement I can see the tip of the fork & the axle rapidly stuttering when I brake but there isn't any noticeable sound from the brakes (squealing, scratching, etc.). Still, there must be something about the way the brakes are gripping (maybe I have fancy anti-lock brakes on there)...

[maddslacker offline]

Is it stuttering up and down? Or front and back.

I bet 650b bikes don't have this issue.

[jeff]

Actually, it seems to be stuttering front to back, almost like a wobble.

[jtorlando25 offline]

Are you using Avid rotors?

I've had that issue with BB5s, BB7s, and most recenty (last week) Elixir 7's. I've fixed the issue with Hayes rotors every time.

If you take some high grit sand paper to the pads and wet sand the rotors (w/ alcohol instead of water of course) then re-do the bedding procedure, it will go away for a while until the pad material bonds back to the rotor. Then you'll be in the same boat.

[jeff]

Yes, they are Avid rotors but the thing is I've been running these (and other Avids) for thousands of miles with no issues. Will try sanding the rotors or maybe even swapping them out - will keep you posted.

[maddslacker offline]

If it's front to back, check the rotor to make sure it is true.

Also, with it on the stand, spin the wheel by hand and gently squeeze the brake to see if it engages the rotor smoothly and evenly.

My guess is that the brake is not gripping smoothly and you're just feeling the symptom in the fork, however, it also wouldn't hurt to stand over the bike, lock the front brake, and move the bike back and forth .. the same way you would test for a loose headset, to see if there is any play in the fork at all.

I had a similar issue on my previous bike and it was ultimately resolved by cleaning the rotors and lightly sanding the pads.

[maddslacker offline]

My front brakes just started exhibiting similar behavior. In my case, the rotor bolts had loosened, allowing the rotor to rotate a bit on the hub. I re-applied some blue locktight to the bolts and now they are back to normal.