djb

Just to be clear, I didnt put this in "mechanics" just because I figured more touring folks would see this....
will try to make this short (ish)

have had a disc brake bike now for about three years, and have had to learn, figure out, muck up, muddle my way through stuff with them, but all and all like how they work for loaded up touring, especially in mountains.

comes down to having to learn new techniques to work on them, and without getting into specific models and such (mine are tried and true Avid BB7's that work perfectly fine for me and while one piston, give me ample braking)
the one thing I figure any of us with discs will run into are noisey, screeching brakes at some point.

my bike started this on the front brake last year, and got worse and worse, and actually started with new pads I put in for my Mexico only trip, the Central America trip pads were getting a bit thin but figured I'd just change them given that I had spares.

The screech started out slowly, and would go away with slightly harder braking, but got worse and has been annoying for a long time now.

Figured it was contaminated pads, from having wheel off for air transit, and maybe getting something on the cardboard stopper I stuff inbetween the pads in transport.
I tried taking out pads, cleaning with alcohol etc, car disc brake cleaner, no change.
I tried sanding away the top layer of pad, no change again.
Cleaned rotors with alcohol also during all this, no help.

so kind of just lived with it until the other day
repeated the same stuff, no help
even took out my propane torch and cooked the pads, no help

but then saw this webpage that describes sanding away the ridges that form, and my front disc looked very much like this one, in the "before and after" photo, "figure 2"

https://www.bbinfinite.com/blogs/new...isc-brakes-now

I just used some metal sandpaper I had around, did it by hand, didnt even take the rotor off, but worked my way around with reasonably pressure, always going perpendicular to the streaks.
Tried a moderate amount of sanding, not that much, until they looked scuffed up, but didnt over do it either

and voila, after doing the prerequisite multiple hard brakings to transfer pad material to the rotor, it seemed ok.
Went for a loaded up ride yesterday to really test it out, and finally the screech is gone.

it actually makes sense, after each time of cleaning pads , sanding pads, I could feel even more with light braking , a fast "pulsing" going on (maybe more after cleaning cuz the pads were more "grabby" with fresh material exposed.)
and this pulsing is what sets up the high frequency resonating vibrations that create the screech , think how a violin bow going over a string makes it vibrate and creates the high sound, and violinists put resin on their bow strings to create "grabbiness"

so it would appear that as my rotors wore, and ended up with grooves in them , just like the photo shows, the sanding removed the ridges, and hence the vibration causing pulsing.

anyway, I just figure that more and more of us are using disc touring bikes, and its nice to be able to deal with stuff on your own, and to have a better understanding of fixes.

I wish I had figured this out last year, but there you go. I probably could have just sanded the rotor and not done any of the mucking around with the pads, and it would have fixed it.
Hope this helps some of you a bit.

ps, rotor thickness does need to kept an eye on, and a proper mechanic will have a gauge to check if your rotors are getting too thin, so be aware of this, especially with sanding going on. I will ride by a shop and have them check the thickness out again, did it last year, but will make sure.

conspiratemus1

Thank you very much for posting this helpful how-to. I'm going to print it off and hang it over the workbench to remind me what to check next time I hear squeal.

Mr. Wiggles

I’ll try this. I only have 1100 miles on my new Surly Trucker and the front disc has started squealing like a pig on the way to the slaughterhouse.

thanks

djb

I'm no expert, but that's only 1700-1800 kms, I wouldn't think your rotor looks like in the photo, like mine did.
At that mileage my front brake was quiet ish, so it might be a contamination issue.
Who knows.
Well, you will get better at taking out and putting back in pads, which I found a bit tricky until I figured getting them in mostly in, and lined up properly and clip always in right position and pads in clip properly--and then giving them a little whack with a screwdriver handle to make sure they "click" in place.

Bottom line, the more you muck around taking out and putting pads in , the better.

Inspect the pads to see if obvious oil stains or something , but I guess just good luck with trying the various steps.

I was impressed about how long my front pads lasted.

Good luck finding solution
Doing one step at a time is better to know which one it is. Like all troubleshooting.

conspiratemus1

In that case (and if your bike's not a tandem), the rear pads should last forever.

djb

My bike still has the original rear pads on it from when I bought the bike.
So they've done riding with first owner in mtb guise, me riding bike around through various handlebar setups, Central America, 1/3 ish of Mexico, crossing France, a week long supported trip, and some other riding this summer....
So yes, I'm impressed.

Thread I made sometime after Central America about pad life

https://www.bikeforums.net/touring/1...ld-vs-new.html

But remember, this is my experience

seeker333

Your rotors are likely in good condition. Replace pads with new Avid pads.

BB7 calipers cause the brake pads to wear in an uneven manner - they quickly lose their flat braking surface, so that the surface area of pad which contacts rotor is reduced, which compromises braking and causes increased braking noise. Until the pads are quite worn, you cannot see the uneven wear, but if you have a digital caliper you can measure it long before you see it. IIRC, pads generally wear so that there is a high point in center and low points along the leading and/or trailing edges. Use only Avid brand pads. More comments on this topic here.

djb

Hey there seeker, thanks again for your more experienced take on things.
Don't you think given the mileage on those pads it's that worth him just taking them out and doing the clean, sand of them in case they have surface contamination?
I remember finding removing and putting back in pads to be a bit frustrating/awkward because I wasn't doing it properly, so I'm actually glad I messed around with doing this numerous times because at least now I know I can do it properly and fairly easily.

I also now know to have a tiny pair of needle nose pliers and a small screwdriver in my "trip" toolkit.

I didn't have pliers with me in Central America, and one day on a particularly hot and steep climb in Honduras (the norm) there were a pair in the middle of the road as I went past at 5or 6kph, turned around and voila, had a pair.
Switched them out for a light pair for the following trip....

DropBarFan

Interesting, I hadn't read about sanding rotors. My BB7's with stock pads always squealed in the rain; SwissStop organic pads were quiet but wore out relatively soon. Recently bought Jagwire semi-metallic pads to see how they work.

Brett A

Someone please chime in if I'm missing something, but you only need to put a wedge between the pads of hydraulic brakes to keep them from overextending, causing them not to withdraw into the calipers, necessitating you push them back in with a large screwdriver or specialty tool. Mechanical disc pads, OTOH, can be actuated without a rotor in place without any issues. Or at least I've had no problems with my mechanical discs in the 19 years I've had them on bikes.

djb

mine always were the same in rain and or high humidity even if I recall, but ok when dry--but the dry screech was clearly getting worse as time went by. It used to quiet up with a certain amount of harder braking, but seemed to get worse, ie doing it with moderate braking , so thats why I figured I'd try to deal with it, and then saw the article about doing the rotors with sandpaper.

I realize though that writing about sanding doesnt really give a proper idea of how much I sanded, but I did clearly take it easy, not wanting to overdo it for no reason and taking away more rotor material than needed.

basically a learning experience for me.

kingston 

This is the same as my experience with BB7's. The squealing will return, and you can do it all over again. So much effort for so little improvement over cantilevers IMO.

djb

Im learning here still, but here is the story.

I did this the first time flying with the bike, simply from not wanting to have to deal with a possible issue, wasting time and having to figure out a new problem at the start of a trip--so I figured it couldnt hurt to jam some clean cardboard in there when I boxed the bike.

on one flight, my handlebars shifted and most likely had the front brake lever get pushed on hard--and maybe combined with I think the cardboard having fallen out--in the rides post rebuilding bike after trip, at one point the lever moved in suddenly after a harder braking action, and an audible "click" happened.
What I think happened is that the pad got pushed out a bunch, and when I set up the bike again, I had to back off the piston and stuff, and didnt twig to what had happened. The hard braking pushed the pad against the rotor, and then everything popped back into its normal position, and I had to reposition the adjustment dials for the piston and non moving other side.

I think this is what happened, so if Im right, this confirmed to me that its better to have something in there, in case your lever gets pushed on hard while in a cardboard bike box in transit. Depends on your bars, how the levers are open to getting whacked etc.

have you heard of this sort of thing happen before?

djb

I'll certainly see.
On the positive side, I really was impressed how well they worked for such a long time, and having done a fair amount of loaded riding in big mountains with cantis over the years, the extra braking power of mechanical discs with less finger pressure has sold me on them for these sort of conditions, not to mention the clear advantages in gritty, mucky downhill riding for rims.

but there certainly is a learning curve to all this stuff, and a certain pain in the rear aspect until you sort things out and learn the new techniques.
Even just putting a qr front wheel back in and having to futz around with getting the alignment juuuust right, to avoid rotor rub, is one thing that isnt for everyone.

kingston 

Perhaps if you do a lot of loaded touring in the mountains it's worth the trouble. I spend most of my time in the midwest so I have all the headaches without any of the advantages. I switched to hex-key skewers because it took forever to get the front wheel aligned just right with with the QR, and I never have been able to eliminate the rub without excessive free-play at the lever.

djb

and you know what, I would tend to agree with you.
Yes, for mountainy stuff, and gritty wet dirt road stuff over long periods of time, they clearly have an advantage. That said, I think its realistic to say that a lot of our riding isnt like that, and rim brakes work fine for most of our experiences. If I had to take a front wheel off regularly, it would get a bit tiresome getting the wheel just right, but I guess thats why thru axles are the thing, although my understanding is that there certainly is not a standard for that.

no clear clear answer, but as someone who uses bikes with cantis mostly, they do the job, but I do also appreciate disc stuff.

edthesped

I run HY/RD's on two and hydraulics on one and canti's on another. Early on I was indifferent regarding disc and canti's but am now fully converted fan of discs. One bike has at least 5k miles on it and the pads still have plenty of life in them, though there's a distinct ridge in my rotors but not enough to make me want to replace them. I've done minimal adjustment to my discs since installing with the primary need to adjust coming after a wheel pull. Initially I would just loosen the two bolts holding the caliper and re-tighten while squeezing the brake. Now, if I do a wheel change I flip the bike upside down, tighten the skewer and shine a flashlight on the back side of the caliper while I spin the wheel, if the gap between the pads appears even I'm done, if not I tighten or loosen the skewer as needed, though I now use the DTSwiss RWS skewers and am better able to tighten my wheels by feel so rarely have an issue after pulling a wheel.

venturi95

Cantilever squeal works better than a bike bell. I agree discs can be finicky, I hate things rubbing that shouldn't be rubbing.

seeker333

TL;DR version: no

My BB7 rotors have never developed anything more than microscopic scores - even magnified 10x they look tiny - but I no longer bicycle off pavement or in winter rain/snow. I expect MTBing or lots of off-road use would change this situation. In my road-only experience, BB7 brake pads seem to wear out many times faster than rotors, and I believe this is by design. My new Avid rotor measures ~1.88mm thick, and my used rotor with ~2,000 miles ridden measures 1.95mm thick, which tells me that a. there has been variation in rotor thickness over the years and b. rotors don't seem to wear much the way I use them.

Since Avid (and most others) rotors are under 2mm thick, and I know they can be warped much easier than they can be straightened, I lean towards not recommending anyone attempt to refinish a brake rotor. The prudent solution to is to replace pads and/or rotor with new Avid parts and remount rotor with threadlocker compound. New rotors are not cheap but they are much less expensive than medical or dental care, lost wages due to injury, collateral bike damage from a rotor failure/crash, etc.

The problem with hand-refinishing a scored Avid rotor is that it starts out new <2.00mm thick. If you have scoring with a depth up to 0.25mm on each side (that's only 0.010"), and sand this out, your rotor ends up being ~1.50 thick, which is likely below the minimum thickness spec (I searched but can't find a spec for Avid). Also it is unlikely you will remove metal evenly in this process, so you may end up with hills and valleys, resulting in a pulsating depressed brake lever (like the brake pedal on a car with warped/worn rotors), and braking performance as bad or worse than it was with only scoring.

I think it may be possible to have a situation where the pad and/or rotor surface has developed a slick, hard glaze, in which case very light sanding with fine emery cloth/sandpaper might improve braking performance. Not removing much material is critical - the more removed, the more likely you will reach a minimum pad or rotor thickness, and the more likely you will introduce undulations and chattering in the pad-rotor interface.

Can you remove a rotor from hub, screw/bolt it down to a flat surface to prevent warping, then hand sand lightly with 800-1200 grit emery cloth in small circles to refinish without removing much material? Probably. Will this result in better braking/less noise? Maybe. Will this procedure cause a front rotor to fail catastrophically, resulting in injury? Unknown. I don't recommend people do things that might get them hurt, even if I believe it probably will not - I choose to err on the side of caution.

Obviously thousands of automotive brake rotors are refinished (on a precision lathe) in a similar fashion every day with the only result usually being a reduction in rotor runout, reduction or elimination of brake pedal pulsation and slightly improved braking. However, bicycles do not have belts and air bags in case something goes wrong.

Rob_E

I did switch to TRP, but I'd still take BB7s over rim brakes. I am not in very hilly territory, but I do ride in whatever weather comes my way. As a result, I wore right through my rim after a few years of riding with rim brakes. After that I put "disc brakes" on my list of requirements for my next bike. I haven't regretted it.

kingston 

It seems most people prefer disks, so I realize I'm in the minority, but I'd rather replace a rim every once in a while than deal with the constant squealing and fiddling with the BB7's. I can replace a rim in under an hour for less generally than the cost of a rotor and pads. On my foul-weather/winter bike I use drum brakes which last basically forever with almost no maintenance. All my other bikes since my first and only experience with road disks have rim brakes. As I said, I live in Chicago, so we don't have to use our brakes all that much. I might feel differently if I lived or toured in the mountains.

djb

thanks,
I do get not recommending something that could lead to a dangerous situation, and erring on the side of caution is always best.

When I think of what I did, I used a very fine metal sandpaper (not sure what number), probably emery cloth, and I really did do very, very light and very little sanding. The rotor trueness wasnt affected, but as you say, I really need to go to a store where they have a digital caliper and really find out how the thickness is.
It will be interesting to compare the rear and front rotor, and I also have a spare rotor I need to dig out and compare it also.

thanks for the thickness references, and yes that is interesting that the new one is 1.88 and the 2000 mile older one is 1.95

I'll try to get this bike to a store , or ask around to neighbours for a digital caliper, and I'll post the results.

Oh--one other question, I would imagine organic pads are a lot more friendly to rotors than metallic? Ive only had metallic or semi metallic, Im not really sure what mine are, and the spares I have and put in last year look the same as the originals.

anyway, again, thanks for the tips and info.

Brett A

I hadn't heard of that happening before, but it sounds totally reasonable. No harm in taking the precaution.

djb

I'm fairly certain that Ive seen an image of a plastic doohicky with a tab on it, made for doing this, might have even been an avid part.
but I figured some clean cardboard folded and jammed in there couldnt have a downside, as long as its clean I guess.

Bike Jedi

Is this seriously legit and OK to do?? After all the things I have heard about being careful contaminating your rotors and all the things that can go wrong with them...seriously just take sand paper and go against the grain?? Seems wrong without ever doing it, but I actually have a bike I can try this on. I am in similar spot...changed pads multiple times, clean rotors neurotically, and the squeak always comes back. I didn't even know what to do or think anymore about it and just learned to live with it looking forward to a different system one day. This is the only other thing I can try before new rotors and I wasn't going to spend the money on new rotors to find out if that will fix it.

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