Riding home after a really wet and muddy ride I realised the front brake was juddering badly, causing the fork to flex back and forth at a frightening rate. After washing and drying the bike, I could reproduce the problem inside my garage at very low speed, by gently applying the brake and rolling the bike along the floor. It’s as if the rotor has a slippery patch on it every other inch or so. As far as I can tell, all is tight and the bike is pretty new (Whyte T129). Any ideas? Why would this gripping/slipping pattern be so regular? Is it the rotor design? It has the original 180mm SRAM rotor.
Thanks!

Hiya.

Have you checked the headset has no play?

Could also be play in the fork bushes.

That said, my DB5’s always did that to a degree in a new fork with new headset correctly fitted also…

You using Centerline rotors too, as I did?

Yes, all checked and no play anywhere – headset, calipers, fork… everything rock solid. Centerline rotors. I will try cleaning the rotor and new pads. If that doesn’t work, I think I’ll change the rotor… and after that, I’ll buy slx brakes and be happy ever after, I reckon. SRAM has been awful on this bike (which is great otherwise). Fork sent back for warranty repair, shock broken and replaced under warranty, and the reverb just started sagging. All in the first three months with gentle use. Not impressed.

I never did fully get to the bottom of it but I’m fairly sure the rotor design leads to the juddering action on the front fork.

Not at the rear though, on my bike anyway, as it’s just too over engineered to let the brake get away with it.

Let me know how you get on with a rotor change!

I really like SRAM stuff to be honest.

Wouldn’t touch a Reverb though. The new build has the BRAND X dropper going on it.

Would like longer drop but prefer reliability/simplicity more!

Mind you, Brand X bringing out a longer drop version this year. 🙂

Update: changed the pads, cleaned the rotor (which was utterly filthy), bedded the pads in with some hard stops. Problem solved, judder gone, but the rotor was pretty scored so it’ll just start accumulating rubbish again I reckon. Anyway, good ride today, except that my rear wheel now squeaks. Ruled out jockey wheels, chain, etc. so I guess it’s somewhere around the bearings/axle. This T129 is quite princess-like, I find…

I had this, but couldn’t see anything wrong. Got so hacked off with it I binned the rotor, at which point I found the issue.

The rotor was missing 3/4 inch of brake surface from the inside face.

Thanks for update limburger!

Celticdragon, could you clarify what you mean as I think predictive/ imperial might have hampered what you typed?

Cheers bud.:-)

Imagine the rotor is a sandwich of brake surface – core – brake surface.

When I took the rotor off, it looked like someone had milled a 1/2 inch slot through one of the brake surfaces, so everytime the edges of the slot went through the pads, it banged causing judder.

Infact, a picture says a 1000 words

Hmmmm, got (front only) judder on my rival hydros and centreline discs. Bikes only a month old and is my first drop bar bike/time I’ve used sram brakes so just thought it was normal,,,, is it ?
Everything tight and torqued ,Degreased pads/discs last weekend with no change.

😯

That actually has a step on it….

Soft spot in the metal..?

I’ve got DB5s on a nukeproof scout, and have to say I’ve been really impressed by them considering their entry-level status.

I think most of the time these things can be traced to contamination issues.

Celticdragon!

Jeez, a picture does say a thousand words.

How on earth did that happen I wonder?

I reckon it’s like a brake bump on the trail. A tiny imperfection in the surface causes a sudden increase in friction on the exit ramp, which then gets eaten away further and further, with friction and erosion growing.

My own judder was probably caused by the design of the rotor. If you look at celticdragon’s picture, you can see how the cutouts cause variation in the total contact surface (and hence friction), and in the profile of that surface. Especially if a pad is contaminated unevenly across its surface, judder is the inevitable result. Unless I am talking b******s, of course 🙂