Fork judder under braking

On my epic (for me it was epic that i actually rode) 2.5 hour ride today i noticed something I've not had before. When braking up front (magura mt6 disc), i could feel and see the fork lowers juddering.

The forks are rock shock Sid 29er at 100mm travel and are as new, having just been serviced and a new set of lowers fitted (so bushings should not be an issue).

Would i be barking up the wrong tree in thinking the brakes are the causerather than the fork? Pads are also new, but i did spill some fork oil on the rotor the other day, so thinking pad/rotor contamination? I did clean the rotor of course, but maybe some residue?

Any thoughts?

My other hypothesis is that sids are known to be a bit flexy, so a 29er version is perhaps more so?

As the ride went on i forgot about it so perhaps it was the oil on the rotors until it was cleaned away as a result of a lot of braking? I'll be out again soon so will check, but would be keen on any opinions.

Re:

Had the same on my bike, revelation forks and Formula brakes. Changed the brake blocks and it was gone. Cannot explain, the blocks were almost new, but it worked. Possibly sanding down the blocks a bit could also help. The bike probably has a through axle, check and clean the axle and refit.

Re:

I'll see how the next ride goes, as it's possible it stopped part way around. Useful to know that changing the pads helped in your case, though mine are new pads albeit possibly contaminated after the oil spill.

Any other theories?

Re brake fluid contamination, hold pad over hob gas flame and any fluid will be burnt off.

.... but anyway pads are reasonably cheap.

Re juddering, could be contamination, worn bushings or brake rotor type. Many lightweight rotors have big gaps in the braking surface so thr pads catch metal then air and it is this transition that judders.

Take a look at avid hs3 (?) and formula, these are reasonably light ad they have many small holrs as opposed to few large holes.

I think going from 160 to 180 will help as less squeezing is needed.

Re:

Cheers for the feedback.

Lowers and bushings are brand new so i doubt the issue lies there.

Rotor up front is a 180 magura rotor as specced with the brakes.

I suspect it's co tamination and that through the course of the ride, it was burnt through, well that's what I'm hoping as whilst pads are cheap, this was a new set and was hoping to get some use out of them before having to replace.

This was a big enough issue for Specialized to send out replacement forks on their Tri-Cross in 2011.

Replacing the pads sounds like the right idea, try a different compound. If the fork is particularly flexible under braking it may not help. Theres a lot of physics and leverage forces trying to send the front wheel under the bike every time you brake and you may just be unfortunate with a combination of weight, fork design, head angle and so on.

Re:

Sounds like contaminated brake pads/disc.
Sand the pads a little and blast them with brake cleaner.
Also try sanding the disc and use brake cleaner again.
Then do several brake tests ftom 20mph or so to bed the pads/discs in again.

I've just had similar on some XT brakes (contaminated with mineral oil) and doing the above transformed the braking from "meh...." to "right on!!!! :mrgreen: ".

If all that doesn't work then get new pads.

Re:

Had contaminated brake pads on my Voodoo. Wouldn't stop for anything and just squealed like a pig. Someone suggested giving them a bit of a rub with sandpaper and then chuck them in the oven. I laughed but tried it anyway.

Next ride out I nearly went over the handlebars so yes baking them does work.

Re:

Great news. 35k ride today and no judder at the front anymore so I guess the contamination has gone. Just need to get the rear brake to stop better, and dial out a few other niggles with the build.

Might try the sanding of the rear pads. When you suggest bake, how long for and what temp?