Just fitted a new 180mm formula disc with a superstar (cheap) pm to pm adapter on my fox forks. Tightened the whole thing up and headset is tight too. Pads aren’t new btw but did work fine prior to new rotor

Sanded the new disc and pads. Sprayed the whole thing with disc brake cleaner – re bedded them in but the bottom of the forks is visabily vibrating and loosing massive power. I don’t trust it which isn’t the plan. Never had this problem before.

Searched the forum and all advice is to do what I’ve already done

Any advice before I ask the wife? Lol

Adapter on the right way up? Is it a toothed rotor – it may be clipping the claiper.

Whit is actually vibrating? the fork leg?

Go back one step at a time and see if anything is loose.

Also why did you sand the disc? Never heard of that one before.

Put the old disk on.
Problem solved.

My guess if everything really is tight is that It’s nothing more than the fact that you’ve cleaned it so well. In the past after using disc cleaner my brakes have felt harsh and violent. Wash them off some more with water, go play in some puddles and then see what happens. I think maybe they are TOO clean just now…

Also, are your forks rated for that size rotor? What forks?

Is the disc warped or distorted in any way? If you lay it on a perfectly flat surface, or hold it against a window pane, does it lie flat, or is any part of it raised slightly?

If none of that works you might just have to accept that you’ve accidentally engineered into your brake a problem that people have been trying to engineer out for years. A bigger rotor will be exerting a bigger twisting moment on the caliper, the mounts and the fork, changing all the forces in the setup.

Fork judder can be caused by so many things but my best guess is lack of rigidity in a vital component. The brake works and everything clamps up then something distorts and lets the brake off a little. The brake jumps then everything moves back to its original efficient position, grabs and distorts again, and so on setting up a cycle of vibration.

I’ve had this when using a non-standard adapter. Solved by using a different one. I’ve also had rotors which looked fine but obviously had a minute high spot which would bind every revolution. My money’s on the adapter, though

Also had a similar problem when the pads overhung the braking surface, and caught on it’s spokes(brake manufacturers own rotor, specifically for that caliper too), a Shimano rotor with a deeper surface on the front sorted it. Certainly worth checking yours.

my guess is a manufacturing fault with the rotor, either a small thickness variation, or it is out of true vertically.

I did the same up grade on my formula rx’s. The mounts came with the discs. Bought from Evans and it was a straight swap not had any issues

I use a Superstar 180 post to post adaptor on my Reba Race with a Superstar disc- no issues whatsoever.

Sometimes I have brake judder on my Pikes with Avid 203 disc and adaptor, it always clears itself up soon after it starts.

I’ve never sanded a disc either…

I had exactly the same problem with judder. New mazocchi forks and headset. I was using “wavy” aftermarket rotors and it made the bike unridable. I swapped it to “round” shimano rotor (using SLX brakes) and problem solved. I didn’t really notice it with the old forks ‘cos they were completely knackered!!

Try the rear pads in there for starters. It won’t cost anything so worth a try.

Thanks for the responses guys – good stuff

Ok here goes . Fox RL 2010 f-series so they should be compatible with 180 mm rotors
Mount is the correct way around. It’s the bottom of the fork thats visibly vibrating. Like it’s gripping hard, then judders then fades.

Sanded the pad to remove any glaze, sanded rotors to give it something to grip onto (done this for years with no ill effects)

Headset tight, bolt from fork to adapter tight and brake to adapter tight

Is it a toothed rotor – it may be clipping the claiper.

Laid the rotor flat and is good, flat as any other rotor (this rotor is second hand btw) – what’s a toothed rotor Mike?

iolo – Member
Put the old disk on.
Problem solved.

– yup, your bang on and it may have to be put back on

Kayak – that’s what i thought, too clean. Gripping sooo tight the fork wobbles? but that can’t be right can it?

goodgugu – it’s almost flat but not totally flat, i think it’s more than acceptable but maybe i’m missing something?

globalti – Member
If none of that works you might just have to accept that you’ve accidentally engineered into your brake a problem that people have been trying to engineer out for years. A bigger rotor will be exerting a bigger twisting moment on the caliper, the mounts and the fork, changing all the forces in the setup.

Fork judder can be caused by so many things but my best guess is lack of rigidity in a vital component. The brake works and everything clamps up then something distorts and lets the brake off a little. The brake jumps then everything moves back to its original efficient position, grabs and distorts again, and so on setting up a cycle of vibration. lol – never a truer work spoken. That’s exactly what i’ve done and that’s exactly what is happening

Cheezpleez – i hope it’s the adapter cos i’ve added 2 components – an expensive 20 mm larger formula rotor and a cheap pm to pm superstar adapter. it’s gotta be one of those that is now causing the problem that Gobalti beautifully put

coatesy – not sure i understand, it’s deffinatly not overhanging? – when i get my head sorted i will post some pics on flickr – don’t have a head cam otherwise i’d film it but the vibrations are quite shocking

retro83 – Member
my guess is a manufacturing fault with the rotor, either a small thickness variation, or it is out of true vertically.

– again it’s one of the two new components added so yes that would make sense

nwgiles – if the formula adapters went silly money then i would have done the same thing. Everything is formula (even pads) other than the adapter

PolisherMan – Member
I had exactly the same problem with judder. New mazocchi forks and headset. I was using “wavy” aftermarket rotors and it made the bike unridable. I swapped it to “round” shimano rotor (using SLX brakes) and problem solved. I didn’t really notice it with the old forks ‘cos they were completely knackered!!

– now you may have something here – my 160 mm rotors are ’round’, the 180 mm is wavy. ahhh, ok we might be getting somewhere now

martinxyz – when i installed the new rotor i swapped the front and back pads round as the back are always near new – i haven’t swapped them back yet but like you say, worth a try

thanks guys – love you all

What brakes have you got?
I’ve got XT, and I changed my rotor from the standard Shimano to a Clarks, one of these:

I had really bad judder with this, and the same on my other bike with the same brakes and rotor. Both rotors were straight and true, so got a couple of different rotor, ones without ‘teeth’, and everything was fine! I can only assume that the teeth were somehow catching slightly, maybe due to the pad shape.

Also had a similar problem when the pads overhung the braking surface, and caught on it’s spokes(brake manufacturers own rotor, specifically for that caliper too

Yeah me too. Only fouling the ‘spokes’ of the rotor by a mm or two but t’was enough.

As the different sections of the disk are swept by the pads during braking the area in contact will vary, thus frictional force will vary. Hence it grips better where there is a larger contact area and the vibration sets up.

Bead (bed?) your pads in. Might need to rough them up a bit first. Happened to me and was surprised when I traced the actual cause.

Have you got the rotor rotating the right way round?

Had exactly this prob’ last year, changed the new s.s. 203 rotor for an old hayes one and it instantly went away. B.T.W. I usually use formula 180 rotors and think they’re great.

Also had a similar problem when the pads overhung the braking surface, and caught on it’s spokes(brake manufacturers own rotor, specifically for that caliper too), a Shimano rotor with a deeper surface on the front sorted it. Certainly worth checking yours.

This.

I run mono mini’s (older version, ditched MM4’s because of squeal) F&R and they are supposed to be 180/160, but I run them 200/180 on hope adapters.
Rear is perfect, never had a problem ever with it (on various frames). But the front is a nightmare (MM4 rotor has less on the braking surface of the rim), so what happens is pad’s judder from the spokes going round. I could solve it with a more suitable rotor, but a bit of dirt in there and it doesn’t happen anymore.

So its either rotor spokes, flex in the adapter, or a combination which gets the fork wobbling in a harmonic way.

Yup, mine were Mono Minis too, switched to a 6 bolt Shimano XT rotor on the front(concentric braking surfaces, not tapering off between the spokes like the Hope)and juddering stopped. Tried the same on the rear, but the XT 160mm has a shallower braking surface, so still suffered, ran a Deore with no trouble for a short while, then ordered a custom Hope with a 17mm deep concentric surface for not much more than a standard off the shelf part once I knew it was all sorted.

My guess would be that the pads used to overlap the old rotor a fraction and that this isn’t the case with the new one. If you’re getting and ABS pulsing type feel it’s likely that the pads aren’t flat and there’s a lip where they wrapped around the old rotors fractionally and that this can be remedied by either chamfering the pads slightly at the edges or replacing the pads. I had this when changing form Shimano rotors to another brand and the pads were catching on the “spokes” of the rotor – chamfering completely eliminated it. I think some people are overthinking the issue. Gary

What disc brake cleaner did you use and why did you use it on a new rotor anyway ? I have ruined my braking performance with clean streak degreaser in the past .