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Discussion Starter · #1 · (Edited)
I am running Juicy 3s with 185mm rotors. Under hard braking, I get some shuddering in the rear. Not violent shuddering, noticeable, doesn't feel dangerous, more like annoying.

I got some great advice to sand the pads, which I just did. I also cleaned the rotors with acetone. I am unable to replicate the shuddering on the street. Just on steep downhill runs so I can't really test it until the weekend.

My question is, can it be the rear suspension? The bike is a Trek Fuel EX with the ABP link in the back.

BTW, my son's bike is squealing and I already cleaned the rotors. Anybody ever try to put molybdenum grease behind the pads to address squealing?

Thanks.

/bing
 

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Discussion Starter · #2 · (Edited)
After much research and spending time reading the Turkey Gobble Mega Thread, I see that my problem is common to Avid brake users.

To save the next poor soul from having to dig into a 580+ post thread, here is a summary what I have found about brake shudder / judder for Avid brakes.

I don't have a gobble problem, so this is all about shudder.

The reason for our woes is resonance. Either from the brake system or from the combination of the brake and the frame. People have experience transferring the same braking system to another frame and not having the problem. Resonance exhibits itself at specific speeds and with specific equipment combination. Changing something in the mix can change the strength of the resonance or completely remove it. Something in the system is acting like a tuning fork. Therein lies our predicament.

Cheapest and easiest - If your bike is under warranty, call SRAM. They know the problem and will send a fix, with your LBS acting as liason. The fix may or may not work, and your LBS may or may not comp the work done. What is certain is the parts will be free.

SRAM tech bulletin
http://forums.mtbr.com/attachment.php?attachmentid=520555&d=1266096836

FREE fix - align the calipers or align the rotors, or both and torque all the brake fasteners. Chances are you will change something that will change the resonance properties of the braking system.

Fixes requiring parts/supplies - change something in the system. One or a combination of the following will change the resonating frequency, hopefully beyond your riding range:

- resurface the pads by lightly sanding them. I used 400 grit sandpaper. It helps to do it on a glass surface to get a good flat surface.
- apply a thin layer of copper grease on the BACK of the brake pads.
- file the rotors for burs or scrub it with steel wool.
- change the height of the calipers, using washers, in relation to the rotor for better contact
- change the pads to organic or Kool Stop
- change the rotors to a different size or brand
- put a lead weight on your noisy caliper

The Warren Buffet Fix - change the whole braking system with the hope that the new system will not resonate on your frame. Shimanos and Formula users seem to have less judder problems.

As it is, I am waiting on the SRAM fix before I start spending money. The vibration seems to be harmless, at least in my case. All I get is a shudder when descending at very slow speeds while braking.

I changed the title of the og post for easier search hits.

Thanks for the info MTBR!

/bing
 

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Thanks for posting this, I'm in the same boat albeit with a different bike and Juicy Fives. I'm going to try sanding the pads, wiping down the rotors, re-centering the calipers, basically all the free stuff first. If that doesn't work I'll be ordering some Alligator rotors and organic pads.
 

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IF this wont move the caliper too far inboard, try putting thin nylon washers between the mounting adapter and the frame. Deadens the vibration, helped my avids (but still shudders on rare occasions)
 

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I sanded and chamfered the edges of the pads, applied automotive anti-squeal compound to the back of the pads, and re-centered the calipers. I went on a good 2+ hour ride this past weekend and NO noise/vibration! So far so good, and if it holds up for a few more rides I'll call it fixed! Thanks once again for all the info!
 

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Discussion Starter · #6 ·
Even before my warranty parts arrived, I follow advice I got here and sanded the pads (using a glass pane as backing) and cleaned the rotors. Works good now. I have a significantly weaker shudder, but only ever so often. Don't really mind it now.

/bing
 

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Permatex

Permatex Disc Brake Quiet fixed my Juicy 3s. Applied to the back of the pads as well as the spring. Did that about two months ago and have many rides in with the "fix" plus just rode ORAMM (some of it!) and no noise or vibration. Before applying the permatex they howled. Giant XTC1 29er.
Hope this helps.
 

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Discussion Starter · #8 ·
dustoff67 said:
Permatex Disc Brake Quiet fixed my Juicy 3s. Applied to the back of the pads as well as the spring. Did that about two months ago and have many rides in with the "fix" plus just rode ORAMM (some of it!) and no noise or vibration. Before applying the permatex they howled. Giant XTC1 29er.
Hope this helps.
My son complained about a vibration in his brakes and also some squealing. I cleaned the calipers and rotors with some brake cleaner, then sanded the pads. While I was at it, I sprayed back of the pads with that Permatex stuff. Initially, it look promising. Smoother, no grinding, mucho quiet. We'll testing it on the trail on Tuesday.

The Permatex puts on a tacky rubber coating on the back of the pads. Eeeeenteresting.

/bing
 

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Brake problem - Avid Juicy 5

I have an interesting situation and not quite understanding the cause at this point. I flip my bike upside down by lifting the bike from the front handlebars to be able to read the bike serial number, while doing so, I have compressed the rear brakes to lock the rear tire from rolling, so far no issue, bike is upside down at this time. While I still have the bike in the same position, I compress the front brake level and the level compresses all the way to the grip, which made me puzzled, I looked all over for oil leak, but none found. I put the bike right side up on a riding position and continued to compress the brake level a few time, level is still compressing to the grip. I wait for about 1 minute or so and tried to compress the brake level and level returns back to normal, level never reaches to the grip. The rear brake level doesn't do that, why would the front do it? Keep in mind I did this a few times in the same order that I explained it on top.
 

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Camster said:
I have an interesting situation and not quite understanding the cause at this point. I flip my bike upside down by lifting the bike from the front handlebars to be able to read the bike serial number, while doing so, I have compressed the rear brakes to lock the rear tire from rolling, so far no issue, bike is upside down at this time. While I still have the bike in the same position, I compress the front brake level and the level compresses all the way to the grip, which made me puzzled, I looked all over for oil leak, but none found. I put the bike right side up on a riding position and continued to compress the brake level a few time, level is still compressing to the grip. I wait for about 1 minute or so and tried to compress the brake level and level returns back to normal, level never reaches to the grip. The rear brake level doesn't do that, why would the front do it? Keep in mind I did this a few times in the same order that I explained it on top.
Your brake needs a bleed. There is an air bubble that is rising into the caliper when the bike is flipped upside down.
 

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Discussion Starter · #12 ·
UPDATE: So no more juddering, but I do get the squeals every now and then. Ive resorted to blasting the calipers and pads with brake cleaner. Its important to CATCH THE OVER SPRAY with a rag on the opposite end so as not to damage the hub lube.

It will squeal for a very short while thereafter, but after re-bedding, they'll be fine for a few rides, until they get dirty again.

Seems like an acceptably cheap and easy solution to keep my Juicy 3's quiet (I maintain 2 sets for myself and my son). Not permanent, but they are working good, and it takes less than a minute for the maintenance. Strong, not grindy and mostly silent.

/bing
 

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I have maintained for some time that the root cause is the stamped vents in the rotors. Here is some indication from Avid that this is indeed the root cause (taken from Universal Cycles' website):

"G3 SolidSweep rotors are designed to help eliminate resonance/vibration in certain frame/wheel/brake configurations by removing cutouts in the rotor braking surface"

The SolidSweep rotors have no vents.

I'm not having a good experience with Avid's organic pads. After >1k quiet, vibration-free miles on the semi-metallic pads, I switched to organics and now have both noise and vibration. I believe what's going on here is the organics are softer than semi-metallic, and therefore the leading edges of the pads can grab the rotor vents more than a harder pad. The organics do have more grip, but not enough to justify my bike feeling and sounding like a piece of crap. Do note that I have the alloy-backed organics, so there is a chance the standard-backed ones would perform differently for me.

People need to keep in mind that anytime they loosen the caliper mounting bolts, they're re-aligning the caliper, even if only slightly. Therefore, if you do something like sand or change your pads and it affects the noise/vibration, you cannot know whether the re-alignment, the pad change, or both affected the problem.

Anything that causes the forces on each of the pads in a caliper to be different is going to cause some vibration as the difference in force attempts to twist the caliper from side to side. The magnitude of the vibration is largely dependent on the rensonant properties of your entire bike setup, so it's possible to have a fair amount of vibration at the caliper that is not objectionable to the rider, while the opposite is also true. Because the rotor vents are stamped, and not quite perpendicular to the rotor surface, you will get a different amount of force on each pad as they pass the rotor (no material is perfectly rigid, so the pads do slightly catch the edges of the vents as they pass).

Slightly filing down the 'sharper' (outboard) edges of the rotor vents worked for me. I did this with the rotors on the bike, so the calipers were not re-aligned during the process, nor any other changes made. Of course, I can't make the new organic pads quiet even with another round of filing, so I think I'm going to return to the semi-metallic pads soon.

-Pete
 

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So, another update: noise has come back. Same thing, squeak in the front, shudder/gobble/wharlgarbl in the rear. Sanding and applying the automotive brake quiet compound to the back of the pads worked great for 3-4 rides and now it's back. I'll probably sand them down one more time and REALLY shave down the leading edge which seems to be a big part of the problem. If that doesn't work, then it's Alligator Serration rotors and Alligator pads for me...I sure am done with the noise.

Also, I noticed that after some longer descents the brakes will quiet down some, only to return after they cool down. And if I grab the rear brake hard, I don't get the noise/vibration. It's only under light to medium pressure that I get the shudder.

EDIT: I've also sent in an email to BikesDirect to see if they will cover this under warranty. I've heard of people getting shipped new rotors and/or pads as part of the warranty. I hope this will be the case.

EDIT: Called Avid and they said to handle it through ANY bike shop, but they may require proof of purchase to verify you are the original owner of the bike. They mentioned this is a known issue and they will work with the shop to send out new pads and rotors, depending on what rotors are currently on the bike. They said that there are some rotors that were manufactured with "uneven thickness" and this contributes to the problem. They also said they cannot deal directly with a customer and you have to go through a bike shop.

EDIT: BikeDirect got with Avid and sent two G2 Cleansweep rotors and two sets of organic compound pads. Going to throw them on tonight and see what happens over the next few rides. I'll report back my findings.
 

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Discussion Starter · #15 · (Edited)
I think Ive completely solved my squeal / judder / turkey gobble problem. Not a perfect solution, but its good enough. Ive used my bike about 12 times since I last blasted it with Brake Kleen. No problemo. Its as quite as a baby. It was time for its monthly cleaning and inspection so I washed it with car soap and water. Turkey gobble came back.

Blasted the calipers again with Brake Kleen, making sure to catch the overspray with a paper towel, and the noise is gone. One paper towel, a spritz of brake cleaner and 3 minutes :) Make sure you get both sides of the pads and use enough cleaner to wash them out. Wipe down the rotors while the towel is still wet from overspray. You"ll be surprised how much stuff comes out of a perfectly clean set of calipers. It's not necessary to take out the wheels. You do have to bed the brakes a bit, a couple of stops to get that last squeal out.

Considering Ive got the noisiest disc brake in existence (2 sets of Juicy 3s) I think I'm doing good. However, next time I wash my bike, I'll bring it over to the lbs and hit Avid up for a free set of pads and rotors :)
 

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Avid Elixer CR mag Turkey Gobble

I had bad turkey gobble front and back. My carbon 2010 Stumpy came with metallic pad so Avid sent me thru my LBS some organic pads. Didn't work. Then they sent me another set of organic pads and a new set of G3 rotors. Didn't work.

To brake up the "resonance" I put a used metallic pad on the right side of the disk and a organic on the left side of the disk on the front wheel. Still good after one 2 hr. ride. The others so called fixes that Avid suggested lasted 15 minutes.

I'm going to try it on the back and see what happens. I'll let you know.

Wolvie
 
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