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Technical Q&A with Lennard Zinn – Brake squawk

  • By VeloNews.com
  • Published Feb. 17, 2009

By Lennard Zinn

Shimano has plenty of advice about keeping these quiet.

Photo:

Disc brake squeal

Dear Lennard,
I have a Santa Cruz Blur Classic with full XTR components. Now on my third year with this setup and suddenly both disc brakes are squealing like mad. I had replaced the old Shimano metallic pads with new Shimano metallic pads and the noise started.

I switched to Shimano resin pads and they are no better. Cleaned and lightly sanded the rotors, no change. Double checked, everything is tight, how do I get it to quit? New rotors? They sound like the old V-brakes when not adjusted properly.
Pat

A thorough answer from Shimano

Dear Lennard,
When disc brakes start making noise there are several possible causes. Let’s take a look at some basic categories. For elaboration on these topics, check out the tech tips section of our website.

First, there are different characteristics of different pads. It sounds like Pat already knows about this because he mentioned that he tried our resin pads. There is a chart on our website that describes those different characteristics but the important thing here is that some naturally make more noise than others.

The next thing to take a look at is the proper procedure for changing the pads. The basic rules are: always clean pistons before pushing them back into the caliper and always loosen the caliper mounting bolts before pulling the lever to bring the new pads out to meet the rotor. The reason for those rules is that we are trying to avoid an imbalance between the pistons that can lead to reduced performance. In some cases an imbalance can lead to brake noise, so this is a good place for Pat to start. Check out the “Brake Reset Procedure” on our site for step by step instructions on getting rid of that imbalance.

The fact that Pat mentioned he tried cleaning his rotors tells me he is also aware that contamination can sometimes cause noise. It is possible to clean a rotor but personally I have never been very happy with the results of trying to clean or sand them – replacement is a better option. The key to avoiding frustration here is to remember that just a little bit of braking can be enough to transfer contaminants from the rotor to the pad so when troubleshooting, always replace pads and rotors together. This is one place where the mechanics at the local bike shop have a big advantage. They can put on fresh rotors and pads to see if the noise goes away. If so, great. If not, they put the old ones back on and you didn’t have to buy anything to find out your old parts were fine. Actually this brings up another rule when dealing with disc brakes: never put the old pads back in when changing rotors.

That segues nicely into a brief discussion about rotors. If they get overheated – replace them. There is no saving an overheated rotor. You can usually tell if a rotor has been overheated because it will have some discoloring and, of course, it will make noise. It is possible that Pat’s rotor became overheated on his last ride on the old (likely very thin) pads and now he is hearing the consequences of that overheating. There is a document on our site called “Brakes and Heat” that goes into more detail.

Rotors also need to be burned in properly. If they aren’t they can have decreased performance and, again, make noise. This is a possibility in Pat’s case because if a strong chemical was used to clean the rotors they may need to be burned in again. The proper burn in procedure is available online.

Finally, there are several alignment and torque issues to think about. The wheel might not be straight in the frame or fork. The caliper might not be perfectly aligned with the rotor. There may be play in the axle allowing the rotor to move independently of the caliper. The quick release skewer may be loose, allowing the wheel to shift while riding. The caliper mounting bolts may be loose. Any of these things can cause brake noise, and a wheel being not settled in the drop outs has gotten the best of many quality mechanics.
Nick Murdick
Multi Service Technical Representative
Shimano American Corporation

New brake pads or earplugs?

Dear Lennard,
I recently bought a set of Roval carbon wheels as part of a bike upgrade. Great stuff, but I cannot stop the incredible brake pad squealing which is present front and back although much more annoying on the front because of the extra loading.

The bike came with Swiss pads but I have exchanged these for Coolstop and more recently with Dura-ace with no improvement. The pad alignment is good and it seems more a problem with the carbon contact area which is showing an irregular wear pattern which likely explains the fact that braking is associated with a grabbing as though the wheel is out of true (which it isn’t). This has gone on for almost four months as I was told it would gradually resolve! Now I am finding it tough to find riding mates who don’t wear earmuffs. Do you have any ideas?
Dave

Answer from Specialized

Dear Lennard,
I would have him get rid of the Dura-Ace pads, as we found that that type of pad generates a lot of heat and we have seen people melt rims. The Roval pads are made by Swiss Stop and they work well, also the Corima pads seem to work great.

The grabby feel is a tough one with Carbon rims as you know you can’t machine the side wall, so some start with a slight grab but it will get better, I think that as he has persevered for four months he should call our customer service department and discuss it with them, it may be a case that they would replace or re rim the wheel but he should talk to them.

Another thing is if people are heavy on brakes the rim and pad glaze and it is a good idea to sand the pads and clean off the rim. You can also use a fine sand paper and sand the rim to remove any build up, this will also help get rid of the dreaded brake squeal, but it is definitely more of a problem with Carbon wheels than with Alloy.
Nicolas Sims
Specialized

Dear Readers,
In last week’s column, I mentioned adding a couple of spacers and a second wavy washer to get a Campagnolo Ultra-Torque crank to fit in a Trek Madone BB90 shell. The wider bearing-to-bearing distance mandates more spacers, and Trek puts these into its Campy UT kit, and this is an easier, foolproof way to do it – much better than trial and error using my suggestion from last week.

Here are instructions from Trek:
The bearings and seals that come pre-installed onto the Campy cranks are actually 92mm wide at the seal location. There is a specific kit required for the Madone that has an extra spacer (between bearing and frame) and then two rings that get loctited into the frame. Those rings provide a location for the Seals to run against (widen BB shell from 90 to 92mm). See the assembly manual. The Trek PN’s are listed below.

TCG # 08 Trek Madone Bottom Bracket Parts
• 404699
Trek Madone BB Bearing Kit – Shimano
• 411813 Trek Madone BB Bearing Kit – Shimano – Ceramic
• 404700 Trek Madone BB Bearing Kit – Bontrager – SRAM
• 411814 Trek Madone BB Bearing Kit – Bontrager – SRAM – Ceramic
• 408957 Trek Madone BB Bearing Kit – Bontrager – SRAM (Triple Spacer Add-On)
• 407383 Trek Madone BB Bearing Kit – Campagnolo
• 407382 Trek Madone BB Bearing Kit – FSA – Mega Exo AL Cranks

Also, we are in the last weeks of approving a kit for the FSA carbon cranks. They have the opposite problem that the spindle length is only 88.5mm long, so we are trying to pack bearings and seals into a more narrow envelope.
Tyler Pilger
Trek Bicycles



Technical writer Lennard Zinn is a frame builder (www.zinncycles.com), a former U.S. national team rider and author of numerous books on bikes and bike maintenance including the pair of successful maintenance guides “Zinn and the Art of Mountain Bike Maintenance” – now available also on DVD, and “Zinn and the Art of Road Bike Maintenance,” as well as “Zinn and the Art of Triathlon Bikes” and “Zinn’s Cycling Primer: Maintenance Tips and Skill Building for Cyclists.”

Zinn’s regular column is devoted to addressing readers’ technical questions about bikes, their care and feeding and how we as riders can use them as comfortably and efficiently as possible. Readers can send brief technical questions directly to Zinn. Zinn’s column appears here each Tuesday.

FILED UNDER: Bikes and Tech

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