# Disc brake "knocking"



## Vettevert (Jul 15, 2012)

My rear brake knocks for the lack of a better term. It is a thumping that can be heard and felt and only happens when braking. The rotor is clean and the caliper isn't loose.

Any ideas?


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## eb1888 (Jan 27, 2012)

Flip the bike and crank it and lightly apply the brake to see more about what is happening. It may be out of adjustment and one side of the pads(which is the moving side) may have the push the rotor to far to hit the stationary pad. OR
The rotor may only hit at one point. and be warped.


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## cobba (Apr 5, 2007)

Post a side on photo of the brake/rotor set-up.


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## Zuarte (Nov 21, 2010)

Make sure the rear wheel itself is seated squarely in the drop outs. 

While you have the bike upside down and the rear wheel still in place, look through the rear caliper for that tiny gap that should be on either side of the brake rotor. This will work easiest if you have a bright background to look against, as the tiny gap will be easier to see. Slowly spin the wheel, and if you have a warp, it will be easy to make out. I had the same symptoms as you on a rotor, and it didn't take much warp for the shudders to happen under braking.


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## jetboy23 (Jun 14, 2011)

Are these Avid brakes? I would get loud turkey warble and a thunking vibration all the way into my handlebars until i switched to organic pads. Even then, there was a slight vibration.

Your pads may also be hitting the rotor arms. There are way too many possibilities to narrow down without knowing more or even experiencing first hand. If you can't figure it out visually, i would pay your LBS to look into it. Brakes are NOT something you want to chance their functionality.


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## Vettevert (Jul 15, 2012)

Was going to try to recenter the caliper on the rotor using tips I picked up here. I was concentrating harder on how I was going to squeeze the lever while tightening the mount than which bolt I was loosening. Loosened the caliper bolt instead of the mount bolt...squeezed and lost a good bit of fluid. So now I ordered a bleed kit to try and get back to where I was 

Live and learn I guess...


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## Berkley (May 21, 2007)

Hub might be loose?


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## Spec7 (May 3, 2000)

Need to know what kind of brakes they are before anyone can better assist. The current generation of Shimano brakes tend to knock when you first apply them, however its not that big of a deal.


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## Vettevert (Jul 15, 2012)

Brakes are Avid Elixer 5s. Left that part out since as soon as Avid is mentioned, threads seem to get derailed 

Can you explain what you mean by loose hub? I'm assuming you don't mean the maxle. I did notice that removing/reseating the rear wheel did make a difference in the knocking...it got worse. Does that make any sense?


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## Vettevert (Jul 15, 2012)

I should also mention that this is a brand new Salsa HT. This noise/thump started happening on the 2nd ride.


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## SchnitzelNinja (Apr 20, 2012)

Vettevert said:


> Can you explain what you mean by loose hub


I'd assume they're referring to the bearings. Check if there's any side to side play in the wheel.

Also, How many times does this knocking sound happen in a wheel revolution? Is it regular or does it occur randomly?


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## Vettevert (Jul 15, 2012)

SchnitzelNinja said:


> I'd assume they're referring to the bearings. Check if there's any side to side play in the wheel.
> 
> Also, How many times does this knocking sound happen in a wheel revolution? Is it regular or does it occur randomly?


I haven't attempted to count. It happens multiple times per rotation. I will try to count (might be hard) after I get some fluid back in them. Bleed kit is out for delivery...


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## Spec7 (May 3, 2000)

If this started the second time you rode the bike, as long as its under warranty I'd take it back to the shop to get the repair taken care of under warranty rather than fix it yourself.


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## Vettevert (Jul 15, 2012)

Bought online.....


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## jetboy23 (Jun 14, 2011)

Vettevert said:


> Bought online.....


Even then, i would find a local authorized Salsa dealer to take it in. Most "good" LBS's will take care of warrenty stuff. They know that customer service is what will get you back in the door.


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## Vettevert (Jul 15, 2012)

jetboy23 said:


> Even then, i would find a local authorized Salsa dealer to take it in. Most "good" LBS's will take care of warrenty stuff. They know that customer service is what will get you back in the door.


I'm sure I will end up taking it to a local shop at some point, but the closest salsa dealer is 3 hours away...

Bled the brakes. I don't think I pushed hard enough on the plunger to pressurize the system enough. I have brakes again, but they aren't strong enough. I have to squeeze HARD to lock up the rear wheel. I will try again tomorrow. I did loosen the caliper mount bolts, squeezed to center on the rotor, and retightened. Don't hear the knocking any more, so if I can get back the original braking power, I'm good.


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## comphynum (Aug 14, 2012)

what are some good organic brake pads?


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## imcastock (Dec 21, 2012)

sounds like bent rotor or possible hard spot on it?


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## Vettevert (Jul 15, 2012)

Got some braking power back...and the knocking has returned. I am starting to think it is the wavy part of the rotor hitting the caliper. Haven't been able to confirm. I cant replicate it by Pedaling it by hand on a stand...


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## MTBerNick (Oct 23, 2012)

Has to be a warped rotor, easy fix, you should try to straighten it out before you try anything crazy.


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## Zuarte (Nov 21, 2010)

Are the caliper and pads still installed on the bike? Look through the gap between the rotor and the pads while spinning the wheel slowly. Deflections will be easy to see from that.


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## Vettevert (Jul 15, 2012)

Zuarte said:


> Are the caliper and pads still installed on the bike? Look through the gap between the rotor and the pads while spinning the wheel slowly. Deflections will be easy to see from that.


Using this method, I can see no deflections.


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## Spec7 (May 3, 2000)

One other thing maybe....Is the disc rotor bolted tightly to the hub? Years back I thought I was having major brake issues due to weird popping noises happening when I applied the rear brake. Long story short I tightened up the six rotor bolts and the problem was solved.


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## goodmojo (Sep 12, 2011)

Vettevert said:


> Using this method, I can see no deflections.


I know you dont want to believe it but the huge avid threads exist for a reason.

The thumping is probably the turkey warble. Did you bed the brakes?

Bedding means ride 15 times at medium speed and slow to a walking pace
then ride another 15 times at a fast speed and slow to a walking pace.

If you didnt bed them initially you may need to sand the rotors and pads, clean them with brake cleaner. then bed them properly. Also, CRC brake adhesive is cheap and helped me. Cleaning rotor/pads, then bedding worked for a bit, but then the brakes were howling (but not thunking). The brake adhesive stopped the howling (it is applied to the spring to attach the spring to the pads and the back of the pads to attach the pads to the pistons.

I did all of those things which worked, then the levers started losing power. I bled but couldnt get them to work right. I switched to XT, while I was waiting for XTs to arrive I bled again and managed to get even more air out and then the brakes werent bad. However the XTs are still much better.

XTs cost 230 for the pair, trying to sell the elixir 5s for $100.


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## Vettevert (Jul 15, 2012)

goodmojo said:


> I know you dont want to believe it but the huge avid threads exist for a reason.
> 
> The thumping is probably the turkey warble. Did you bed the brakes?
> 
> ...


I'm sure the threads do exist for a reason. Due to them, I didn't have my expectations high from the start. I just felt like my situation was a bit different (being brand new and all), but maybe it isn't.

I did bed in the brakes. I spent an entire afternoon on my driveway (slight descend for the section I used...about 1/8th mile long) following the procedures I had found here, increasing speed gradually. I did not notice the knocking sound during this, and the braking power definitely improved over these passes. I noticed the knocking during my first trail ride.

I will try to clean them with brake cleaner. I assume I only clean the rotor, and keep it off the pads? I could handle the squealing, but the knocking makes me feel llike something is getting damaged. It is mid 20's and snowing currently, but I will try to take some pics and maybe a video of what is happening when I get the chance. Thanks all for the help.

On the XTs. That sounds great....but I barely got the bike wife approved, and she wouldn't understand why I was replacing brand new brakes if you know what I mean.


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## jetboy23 (Jun 14, 2011)

Vettevert said:


> On the XTs. That sounds great....but I barely got the bike wife approved, and she wouldn't understand why I was replacing brand new brakes if you know what I mean.


Let her ride the bike and feel the vibration. She will immediately agree that they are unsafe and require replacement.

Disclaimer: they're probably not unsafe, but, from the vibration i've felt... it can remove confidence on a technical downhill pretty quickly with the shuddering.


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## shwinn8 (Feb 25, 2006)

is the Salas HT referring to the full suspension HorseThief? If so, I'm guessing one of your pivot bearings is shot or possibly a loose mounting bolt.,


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## smithcreek (Nov 27, 2012)

I had some thumping also. Seemed like the most obvious cause was some unwanted contact with the "arms" of the rotor so first thing was to realign the caliper. I could see one pad was contacting first and warping the rotor about .01+" before the other pad contacted. It took about a dozen attempts to get the caliper positioned so there was absolutely no detectable rotor movement, either visual or by feel, to either side when I pressed the brake. The thumping disappeared instantly and so far has not returned.


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## Vettevert (Jul 15, 2012)

I think I am seeing the same thing. I think the pads are hitting the rotor arms...

I have tried many times to center the caliper. Sometimes the thumping gets worse, and other times it cures it...temporarily. I guess I should keep trying. Since making this adjustment changes the problem, it must be what is causing it.


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## Vettevert (Jul 15, 2012)

shwinn8 said:


> is the Salas HT referring to the full suspension HorseThief? If so, I'm guessing one of your pivot bearings is shot or possibly a loose mounting bolt.,


Yes, a horsethief. Bike is new, so I doubt it is shot, but I will check the mounting bolt.

Thanks


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## shwinn8 (Feb 25, 2006)

bearings can fail even if they are new due to poor manufacturing. you never know! just another possibility to look at


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