spectastic

i got a new rotor for my bike. it uses a different brake pattern than the rotor i had before.

when I put it on, I noticed it would be centered, but there's still significant rub each revolution. also, when I brake on the bike, I can feel both the rotor and brake lever pulsate.

things I've tried:
- sand paper brake pads
- sand paper rotors
- re-align caliper
- ran bike up to speed and brake several times to bed in the pads/rotor
- re-true the caliper.

I've more or less been able to get rid of the rubbing. however, the braking is still uneven. I will try to use newer brake pads to see if it'll work. but considering I've already sanded down the previous pads, I don't see how newer pads would help.

any ideas?

dsbrantjr

Try truing the rotor, a pulsation can be caused by a warped one.

aclinjury

a pulsation could mean certain section of the rotor is thicker then the rest (similar to pulsating rim wheel).
You'll need to measure the thickness of the rotor entirely to find out which section may be thicker

drlogik 

Try cleaning both pads and rotors thoroughly with denatured alcohol and try again. I mean really clean them well. Any oil at all will cause problems. Do not touch the pad surface or the rotor surface with your fingers. Wear gloves if you have to. See if that simple fix works.

Just so you know...pads and rotor should break-in together. Unlike a car where it's not as noticeable, on a bike it is. I agree with a previous post about checking the true of the rotor. Even if it's just a little bit off, the brakes will probably pulse. Re-true carefully and try again.

If that doesn't solve the problem....and,

If you can afford it, put some new pads on the calipers and break them both in again slowly and gradually. You shouldn't have to sand either component since they will both be new. If they still pulse then well, welcome to the world of disk brakes! Ain't it fun??

BTW, "cheap" rotors aren't cheap in the long-run. If they are cheap rotors that may be your issue. I've never had problems with high quality rotors and pads.


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spectastic

it's as true as it can be.

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tried different (much newer) pads. sanded the sh** out of the rotor and pads. put everything back together, and it's doing the same thing. I'm sure I'm doing it right. I can feel the brakes become more grabby after each braking. However, the pulsating is still there. I've concluded the rotor is not even. when i look at the 2 parts of the rotor where the braking fads, I see marks that are perpendicular to the direction of rotation (on the inboard side), as if the pad was skidding or something. on the outboard side, I found one mark. I can't explain why it's doing that though. I've sanded that part, and the marks reappear. my best guess is that's part of the rotor that's slightly thicker/thinner than the rest, causing the brake pads to momentarily exert different pressures, causing the skid marks. my caliper measures to the nearest .1 mm, which isn't accurate enough. hopefully this is something that will disappear with time.

drlogik 

Over time they may wear-in and smooth-out. The rotors may be slightly warped by your description of those perpendicular marks.

These things are finicky for sure. Breaking in a new rotor is an important step and there is a process one needs to go through to do it right and avoid pulsing brakes. I'm not saying you didn't do it right but these things are really finicky. Quite frankly I don't like them and only ride them on one bike of mine, a mountain bike.

Try the cleaning with denatured alcohol and a light sanding of both pads and brakes and Google breaking in brakes to see the process. FWIW my first foray into these things came up with the same issues you're having. After going through the proper process with new pads and rotors they are smooth as silk.

fietsbob

Caliper too low? gripping the 'spokes' of the disc and only the inside part of the disc edge ?

Add flat washers under the caliper around post mount bolts. So as to bring it outward ..


Out here we suggest a lot of gentle stops for break in /pad bedding, not a few high speed agressive stops..


...

Kapusta

Bigbus

I had that same problem with a rear rotor on a bike I purchased new. After trying everything that you've done, I replaced the rotor with an el cheapo one I picked up for $2. used from the local LBS and the problem went away. All the sanding and cleaning in the world isn't going to help when you have a bad rotor. Good luck.

base2 

Good advice here. Particularly the bit about the caliper being too low.

Another thing, is "pulse." There is just too many variations to define. I had one bike that had a "Pulse" It was pretty high frequency. After a while, I reasoned it had to do with the cut-outs in the braking surface for clearing mud, etc...The fix was switching to compressionless kevlar wrapped cable housing. Standard coil wrapped housing just wasn't up to the task. It had me puzzled for about 3 years.

I had another bike with IceTech rotors that had cooling flutes. The steel backing on the pad would contact the flutes when the pad wore down. Innocous, but made a tickity-tickity sound. The fix was to take the pad to a bench grinder & grind the overage off the lower edge of the pad backing plate. Works great.

Good luck.

spectastic

i've addressed any possible rubbing or pinging. the rotor is perfectly straight and not touching anything. the one thing i did notice was that when i stand up to pedal, the lateral forces cause the rotor to rub, which is not unreasonable, but not something that happened with the other rotors i was using.

Right now, I'm just going go with bad rotor. I've ordered more that are on their way. they're cheap floting rotors i found on ebay. perhaps they won't have this problem and I just got unlucky

alias5000

Another shot in the dark:
Where did you get the rotor from, is it a cheap one? Cheaper rotors sometimes do not have their surface polished/treated omni-directionally so that the steel has a unidirectional surface pattern on it. You can see that very clearly on rotor D1 in this ebay posting:
https://www.ebay.ca/itm/Snail-MTB-Mo...orCZWeHJc_Asbw
The other rotors seem to be similar.

As you move along the rotor circle, the direction of 'grooves' changes w.r.t to the rotor pad, creating varying brake force as the wheel turns resulting in pulsating braking force. At least this is what I read from other people having tried these rotors.

However, this would not explain the pulsating lever feel.

HerrKaLeun

QR or TA? If QR, I assume you have set the axle in when the bike was on the ground? Front or rear?

I have a fat bike with TA, and never have problems. My hybrid with QR has some "ding" every once a while, no matter what. It has to do with how the frame is loaded as the frame flexes a bit. Sometimes some dirt gets on the rotor, but after some time braking ig goes away.

spectastic

yea i've had experiences with the rotors you describe. however, i've not had a problem with them once they break in. but yes, it is a cheapo floating rotor that cost $8 from HK.

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it's a thru axle.

Branko D

Check if the rotor is torqued well enough (so that it won't budge when you try to push-pull-turn with your fingers even applying force), under-torqued rotors can give you an odd sensation when braking, as it can move slightly.

spectastic

here's a picture of the rotor. I ordered multiple rotors from this company. the 2nd one that arrived doesn't have this issue. notice the inconsistent wear mark at 12 o'clock. for whatever reason, the coefficient of friction on both sides of this mark are completely different. so it's not the thickness, but the material surface that's the cause. there is a similar mark at 7 o'clock, but this one is less noticeable under braking.

alias5000

I think the picture is not showing (at least not to me)

Bigbus

I thought it was just me....

spectastic

F.Ind.

If these go through heat treatment process but issue occurs during that process its possible for harder spots/sections to develop. Quickest way to to find out if disc is the problem is to replace it and leave everything else the same. If pulsating goes away then disc is the problem for sure.

MaxCycle

Just after purchasing an ADO A20+
I am still currently dealing with seller and with ADO support
What I understood, is:
Cheap manufacture and material of discs/ rotor, probably cheap brake pads too.

Replaced with new discs, same issue
Tried to measure with a caliper , same thickness on all circumference, resurfaced a very little, on my workbench, and got precision tools, it's just improved a very little, NOT enough, discs are only 1.82 mill. there is not much to resurface

I am thinking to return the bike or substitute the whole brake system, hope to find a compatible one
Probably you got same or similar issue. Probably are cheap disc

I can keep you posted, if I find a solution. if you want
Cheers
Mx