[RAG2]

Now a new set of brakes, on a new bike, I am again experiencing the front brake pulsating, similar to the feeling of an anti-lock brake. I don't notice when riding aggressively, and I dont suppose it affects performance, but annoys me nevertheless.

I'm currently running Formula Cura 2-pots with the newest design XTR 2-piece rotors. But I previously experienced this issue on my last 2 bikes with Guide Ultimates...i blamed the brakes because I tried several different rotors (RT86, Magura, SRAM Centerline). I even tried 2 different sizes, resurfacing with 600 grit sandpaper, rounding the edge of the cutouts with sandpaper....and of course countless and methodical break-in procedures. But eventually it went away on one bike, remained on the other (both with SRAM RT 86 rotors)...unfortunately, I really do not know how or why it ceased on one setup but not the other.

What causes this?
I initially thought pad material built up unevenly on the rotors, but I've nearly ruled this out now. Instead I think it must have more to do with the cutouts, and/or hownthe cutouts interact with the particular brake pad.

I'm again about to start troubleshooting. Might try a rotor design with more consistent cutouts...maybe one with evently spaces holes such as Hope will help?

Thoughts and feedback welcome, please.

 

[wytemike21]

If you've tried different brakes with different rotors (it's always safest to use same brand caliper and rotor, you can get issues mixing things like sram calipers with Shimano rotors where the full pad doesn't engage the rotor) you've validated that is is something other than the rotors causing the issue. I don't think I've heard of anyone having pulsing on a combo of guides with centerline.

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[LyNx]

Well now, what you usually do in situations like this is look for common denominators, something that's the same across the board despite lots of other varying things and to me that one thing that stands out, is you Have you ever stopped to think that maybe it's user/setup error? That would explain the problem "going away", most likely caused by not properly aligning the caliper with the rotor and getting uneven pad to rotor interface, then once the pads wear to match the angle of the rotor, it goes away.

Just an :idea:

 

[PuddleDuck]

Well now, what you usually do in situations like this is look for common denominators, something that's the same across the board despite lots of other varying things and to me that one thing that stands out, is you Have you ever stopped to think that maybe it's user/setup error? That would explain the problem "going away", most likely caused by not properly aligning the caliper with the rotor and getting uneven pad to rotor interface, then once the pads wear to match the angle of the rotor, it goes away.

Just an :idea:

it could be the bedding in procedure...perhaps somehow unevenly depositing pad material on the disc

see this article for more: Enduro Mag - Enduro Workshop: Fixing noisy disc brakes

 

[RAG2]

it could be the bedding in procedure...perhaps somehow unevenly depositing pad material on the disc

see this article for more: Enduro Mag - Enduro Workshop: Fixing noisy disc brakes

Yeah. I felt like I've done everything right, and for the most part I don't buy into the need to use rotors designed by same company as the brakes (with rare exceptions)...but I'm leaning towards uneven pad material build-up as the culprit. Analyzing my break-in procedure, I've been doing one brake at a time. The front is not stiff relative the back (there's a long axis with a squishy 160mm fork)...certainly that's why you feel it in front and not back, but that also might be leading to uneven buildup since things aren't rigid. I think the uneven cutouts in Shimano XTR design lead to minor differences in friction as they pass over different sized cutouts. I'm gonna grab a fresh rotor i have on hand and try bedding in with both front and rear brake simultaneously and lock out the fork...hopefully the stability of then rear will help the front bed in evenly.

If that doesnt work, I'll order up some Formula 2-piece CL rotors...I'll then be using the correct brand rotor, and more importantly, that design uses an array of evenly sized and spaced circular cutouts/holes.

I'll get it sorted and report back. Fortunately, I dont ever notice it on a run/trail and I'm confident it doeant actually affect performance (and these Curas are the real deal...i have Trickstuff on order...which I might simply cancel).

 

[RAG2]

Darn. I took a fresh XTR 2-piece rotor, bedded it in on the rear wheel first (felt great) and then swapped it up front...pulse/anti-lock feeling present. Ruling out break-in procedure. Just placed order for set of formula rotors...hoping the evenly spaced wholes are a better match. If it happens after this, then something else is going on. Next theory would be that I need to have the brake mounting surface on the fork (2020 Fox 36) resurfaced/trued.

 

[clintj]

Might be time to look elsewhere. Fork flex, fork bushing wear, headset adjustment, etc. Any looseness associated with the front end could let a wobble like that develop.

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[PuddleDuck]

If that doesnt work, I'll order up some Formula 2-piece CL rotors...I'll then be using the correct brand rotor, and more importantly, that design uses an array of evenly sized and spaced circular cutouts/holes.

I'll get it sorted and report back. Fortunately, I dont ever notice it on a run/trail and I'm confident it doeant actually affect performance (and these Curas are the real deal...i have Trickstuff on order...which I might simply cancel).

There's another thread on this brake forum where issues were had due to not "matching rotors" - I think it was for Magura's. In theory the rotor shouldn't matter, in practice, when a bike is a series of components bolted together, each with different characteristics e.g. resonant frequencies...running matching components can matter.

 

[RAG2]

There's another thread on this brake forum where issues were had due to not "matching rotors" - I think it was for Magura's. In theory the rotor shouldn't matter, in practice, when a bike is a series of components bolted together, each with different characteristics e.g. resonant frequencies...running matching components can matter.

Yeah. I hope that's the case here. Matching rotors are on the way, although they weren't available from my normal suppliers so it will be a week. And, fortunately, in all practical trail applications, I've never felt it...its only when coming to a complete stop do I feel it.

 

[scottzg]

issues were had due to not "matching rotors" - I think it was for Magura's.

for the most part I don't buy into the need to use rotors designed by same company as the brakes (with rare exceptions)...

Agreed.

Magura rotors are 2mm where most rotors are 1.8mm, and shimano disks have narrower brake tracks than most anyone else. Can lead to problems from the pads touching the arms of the rotor or such. Also, it's possible to have 6 bolt rotors non-concentric to the hub since the bolt holes have play- that can lead to the rotor touching the caliper in just 1 spot each revolution.

It can be helpful to ensure the rotor is centered on the hub, and you can use a thin washer to space the caliper a touch further out from the rotor.