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Old 2012-09-04, 07:52 PM   #1
uniShark
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Disc Brake Vibration and other Problems

There are various other disc brake threads, but this one is intended to discuss general disc brake problems and, hopefully, fixes.


My issue is that after a few minutes of braking nirvana, my new disc brake developed a loud hum with vibration that is bad enough to shake the whole uni. The problem started up as a slight issue, but then progressed rapidly to the point where the brake is almost unusable due to the extreme vibration. There is no rubbing, hum, or vibration when the brake is not being used.

My setup is a 2008 KH29 with D'Brake, Spirit cranks, 180mm round Alligator rotor, and Magura MT2.

My initial thought was that something must be coming loose, so I checked all the screws that I could get to while on the trail, and everything seemed tight. Tonight I'll strip it down more and re-check.

I've also seen threads on mtbr, with no obvious fixes other than checking the rotor and pads - but mine are new and straight.

Any thoughts?
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Last edited by uniShark; 2012-09-04 at 07:53 PM.
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Old 2012-09-04, 10:11 PM   #2
TopHatPlus
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I had something similar to this on my mountain bike, it ended up the pistons in the caliper were not rectracting properly and were causing some nasty feedback through the entire bike, i had to lube them up and get them working smoothly again. The issue was non existent while the brakes where in use as well, might be the issue?
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Old 2012-09-05, 08:18 PM   #3
uniShark
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Thanks TopHat. How did you go about lubing the pistons? If I take apart the caliper to do that, will it require a bleed job to get the hyraulics working again?

Also, to clarify my issue, the problem is only while applying the brake, and exists every time I apply the brake, even lightly.
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Old 2012-09-05, 09:18 PM   #4
Into the blue
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As with TopHat, I had similar problems with my mountain b*ke.
After buying it second-hand, everything was fine after a few weeks, but after that whenever I applied the brakes there'd be squeaking.
This escalated to actual vibration which could be felt through the forks at the front, and the frame at the back.
It got so bad that I took it to my LBS and it turned out that the problem was the shape of the rotor.
It was one o' them fancy ones, and the guy at the shop told me that basically the uneven outer form of the rotor was causing oscillation every time I applied the brakes.
I switched to round rotors and the problem was sorted immediately, no more noise, no more vibration.
I did a quick google search on your rotor and it looks like on o' them fancy ones too.
Not saying this might be the same problem, but it can't hurt to switch to a round rotor (maybe borrow one off a b*ke buddy for an afternoon) to see what happens.
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I wuld get a 20' trialls uni prolly with a blu tiar.
Get splined an a KH saet or ur a pansy.
Get trials cuz thaz whut i du n u mus wannaa whut i du 2.
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Old 2012-09-05, 09:46 PM   #5
uniShark
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Quote:
Originally Posted by Into the blue View Post
As with TopHat, I had similar problems with my mountain b*ke.
After buying it second-hand, everything was fine after a few weeks, but after that whenever I applied the brakes there'd be squeaking.
This escalated to actual vibration which could be felt through the forks at the front, and the frame at the back.
It got so bad that I took it to my LBS and it turned out that the problem was the shape of the rotor.
It was one o' them fancy ones, and the guy at the shop told me that basically the uneven outer form of the rotor was causing oscillation every time I applied the brakes.
I switched to round rotors and the problem was sorted immediately, no more noise, no more vibration.
I did a quick google search on your rotor and it looks like on o' them fancy ones too.
Not saying this might be the same problem, but it can't hurt to switch to a round rotor (maybe borrow one off a b*ke buddy for an afternoon) to see what happens.
Thanks, but I kept it simple with a round rotor. I figured the wavy/spiky rotors are just for show and can only cause more problems. I got this one:
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Old 2012-09-05, 09:52 PM   #6
Into the blue
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In that case...

I haven't got a clue.
Sorry.
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Quote:
Originally Posted by Harper
I wuld get a 20' trialls uni prolly with a blu tiar.
Get splined an a KH saet or ur a pansy.
Get trials cuz thaz whut i du n u mus wannaa whut i du 2.
lol...awwsum.
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Old 2012-09-05, 10:18 PM   #7
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I had the exact same problem.

Geared KH36, D'Brake, Avid Elixr 5 w/160mm rotor.

After a couple of short rides where it was perfect, it started vibrating, sometime so much that it was almost funny. I was in the middle of a tour in the Swiss Alps, and tried resetting everything but had no luck. So I just put up with it.

By the end of the tour, the vibration was magically a bit less, but still present. I didn't use the brake much at Unicon, but have quite a bit since coming home. Sometime, a few weeks after returning, the vibration has quit completely. When I ride now, even braking really hard, there is just pure smoothness.

I didn't really do anything to fix it, other than to keep riding. I only recently realized how weird (and nice) it is now. I don't really want to touch it now that it's working so well.

Good luck and please post any info/results you learn for this problem.

---Nathan
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Old 2012-09-05, 11:10 PM   #8
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I had the same thing happen using a MountainUni UCM and disk with a Shimano M775 brake and metallic pads.

I ended up switching to organic pads which don't grab as much as the metallics and was very happy with the switch. All my problems went away and my braking became buttery smooth again at the expense of faster wearing pads and slightly reduced stopping power.
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Old 2012-09-06, 02:00 AM   #9
Nurse Ben
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First off, this vibration problem is very common, too common, but it seems endemic in disc brakes for bikes, though auto brakes do squeal on occassion. There is an anti squeal fluid that can be appied to a clean set of pads:


Bike shops usually have a tube of the stuff and might just put a little on for you at no cost, BUT you need to remove your pads.

That said, the OP (Unishark) done good by getting a pair of the new Magura MT brakes, whose pads can be removed from the caliper without removing the caliper from the mount. It is one Torx screw bolt, takes just a minute to pull the pads.

Try a light sand on the pads to remove the sheen, then clean the rotor front and back with rubbing alcohol; don't drink the stuff, it's not good for you

Now try doing some gliding, gentle stops to allow the pads to mate to the rotor without overheating. Some folks like to use water to cool the pads/rotor as they break in, but I find a little gliding downhill braking will do the trick fine.

If you have a repeating problem with squealing, try the antisqueal, or consider getting a different composition pad like Eric suggested. Bigger rotors also cool better.
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Old 2012-09-06, 04:40 PM   #10
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Thanks all.

Last night I did pull the pads, sanded them a little, and did clean the rotor with alcohol (only drank a little ). As noted by ben, the Magura MT pads are super quick and easy to pull out. I didn't get a chance to ride, but shop test (hanging uni, cranking with one hand, braking with other) indicated that this helped but did not eliminate the issue.

Other web browsing reveals that it's common for the Magura MT series to take a little while to seat the pads properly. I jumped right into riding this brake hard on a very steep downhill, so that's probably part of my problem. I'll do some riding this weekend and take it easier on the brake, and hopefully that will take care of it. If not, I'll get organic pads.
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Old 2012-09-06, 04:56 PM   #11
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Also, just to clarify, I really don't have what I would describe as a "squeal." It's definitely a hum. The sound isn't all that unpleasant (although not as good a silent). If it were just the hum, I wouldn't worry about it. The problem is with the really bad vibration (which hopefully won't be nearly so bad after cleaning the pads and rotor).
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Old 2012-09-08, 12:20 AM   #12
Nurse Ben
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You gave me bad luck!!

Now mine started grunting again

Disc brakes are funny like that, I had a set of Tektro, one was perfect, the other caused me no end of sqealing, now I have the same situation with a set of MT2s.

I pulled the pads on my 29er, it has a 180 disc, it worked fine for a ride last week, then today it's back to it's old tricks.

Meanwhile the brake on the 36er (200mm) is plug and play, smooth as silk.

I wonder if it's the differnce in disc size...or the fluid pressure; the lever feel is much firmer on the 29er.
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Old 2012-09-08, 02:18 AM   #13
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Thanks, but I kept it simple with a round rotor. I figured the wavy/spiky rotors are just for show and can only cause more problems.
Well, actually not. The concept behind the first wave rotors was give the same cross sectional area across the entire disc, thereby giving an approximately similar temperature rise across the rotor, reducing distortion. So, the wave extends where there are holes/slots drilled in the rotor and retracts where the rotor is solid. Of course marketing has taken off with the concept, so I'm no longer sure that this is true. But wave rotors were at least initially created to help solve a legitimate problem.
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Old 2012-09-10, 11:44 PM   #14
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I read on a mtbr thread that braking in reverse had helped someone set their pads and stop any problems. So I gave that a try, and fount that although it didn't fix the problem, there was absolutely no noise or vibration braking in reverse. So I flipped the rotor, and carefully aligned the pads, and everything was great. . . for a little while. Then same issue started up again, although not as bad.

I just ordered a pair of Koolstop organic pads, and I'll try those with the rotor oriented properly.
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Old 2012-09-11, 09:33 PM   #15
piranhamatt
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over the summer i was trying out my new disk brake muni, and going down some very steep slopes, and i usually get a very high pitch whine from my disk which i don't mind, but it started to hum, louder and louder, to the point where the whole unicycle was shaking, then, while coming to a stop on a down hill section, the D'brake snapped! the humming must have been it starting to snap, i don't know weather this is the cause for your noise but watch out for stress fractures around the bottom bolt for the calliper
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