Had An Idea Tonight (Disc Brake ‘Pads’ That Are Abrasive Material?)

So, I was thinking about these new shop devices that basically spin your wheel/disc indoors, so you can break them in consistently without riding the bike.
( see Unior Sinter Brake Pad Bedding Machine)

https://uniorusa.com/products/sinter...edding-machine


Well, I was sanding some glazed rotors tonight, and I thought “What if I could make/find some Disc brake ‘pads’ that are really just abrasive material?”
To start with, they could just be a single set to see if it would work, and the next step would be rigging up something like a truing stand with a motor to run a hub.
(I know pro WC mechanics have made these for bedding in, but not necessarily for sanding the rotors).
Any of you jokers have any observations to chime in with?
After my recent thumb surgery, I can’t really do this manually any more. It also would be way quicker.

I did try to make something like this in the 90’s by epoxying sandpaper to some v-brake pads, but you can imagine how well/long that worked.

I think if it was just abrasive pads, you'd end up with linear scoring in the rotor. You'd need some oscillation to properly remove any glaze. Which means it'd realistically be easier to just slap the rotor on your bench and hit it with a random orbit sander. I'd imagine that'd piss off your thumb though.

That is a fair point about oscillation. And yes my thumb (and shoulder) would definitely have an issue with that.

How about mounting a Dremel somehow so you could spin the rotar while Dremel was doing it's thing?

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Originally Posted by toast2266

I think if it was just abrasive pads, you'd end up with linear scoring in the rotor. You'd need some oscillation to properly remove any glaze. Which means it'd realistically be easier to just slap the rotor on your bench and hit it with a random orbit sander. I'd imagine that'd piss off your thumb though.

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I had a piston that was slowly leaking on a long descent and the rotor got all glazed and f'd up. I took an orbital sander with 80 grit to the rotors. They worked ok for a ride or two but 'glazed' back, I don't think I displaced enough material.

How is the surface prepared on new rotors? I speculate the cutouts in them create a raised edge that pads bite on, but that's just my weak ass guess.

Why do you need to sand rotors so often? I don't think I've ever done that, or needed to. Seems like you should either just replace the rotors or figure out what's wrong with your brakes or braking techniques.


sfotex- the ideal situation with a brake is that the pads are heated in an intial bed in process which deposits a thin, even layer of pad material on the rotor. Then braking friction is happening between brake pad and pad material on the rotor which has a higher cf of pad material on metal. Go put new rotors on and try to stop and you'll notice it doesn't work very good, then you ride a bit and use the brakes a few times and things start to work better. With new rotors you should really do a specific, controlled bed in process to get things working as well as possible vs just relying on normal use to create the bed in layer.

Holes and slots and such do help slightly with friction but aren't specifically necessary for brakes to work good and there isn't like a raised edge or anything. The other purpose is to give pad material and other things like pad material, dust, water, gasses, etc somewhere to go instead of being between the pad and rotor. When things get really hot this becomes somewhat important.

I believe holes and slots are more about heat mitigation.

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I figured you dentists used fresh rotors every ride.

No one is questioning the absurdity of a $3k machine that just spins a bike wheel. Shop bros can be the kings of all rubes…


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Originally Posted by nickwm21

No one is questioning the absurdity of a $3k machine that just spins a bike wheel. Shop bros can be the kings of all rubes…


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The alternative is that shop rats take the bike out for a test ride to bed in the pads and spend 30 minutes farting around jumping off curbs. I'm sure for a big shop, it actually saves them money.

Of course, as a former shop rat, if I was told I didn't get to go on test rides anymore because now we have a fancy machine, I'd probably quit on the spot.

FWIW I have to resurface (or replace) my rotors around once a year (every 2500mi). They get too polished. They work 3x stronger afterward. MTX Brakes told me to do this periodically to keep performance top notch. I also clean the rotors every 5-6 rides, it's shocking how much junk comes off.

No one has touched slots and holes? This place is slipping

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Originally Posted by rideit

So, I was thinking about these new shop devices that basically spin your wheel/disc indoors, so you can break them in consistently without riding the bike.
( see Unior Sinter Brake Pad Bedding Machine)

https://uniorusa.com/products/sinter...edding-machine


Well, I was sanding some glazed rotors tonight, and I thought “What if I could make/find some Disc brake ‘pads’ that are really just abrasive material?”
To start with, they could just be a single set to see if it would work, and the next step would be rigging up something like a truing stand with a motor to run a hub.
(I know pro WC mechanics have made these for bedding in, but not necessarily for sanding the rotors).
Any of you jokers have any observations to chime in with?
After my recent thumb surgery, I can’t really do this manually any more. It also would be way quicker.

I did try to make something like this in the 90’s by epoxying sandpaper to some v-brake pads, but you can imagine how well/long that worked.

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https://www.youtube.com/watch?v=zUfWdi0oaLQ

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Originally Posted by The Reverend Floater

I believe holes and slots are more about heat mitigation.

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This is my understanding, but anyone can feel free to chime in to correct me or add detail:

Holes and slots are mostly to get contaminants off the braking surface. At very high brake temps that ‘contamination’ can be gases coming out of the pads. (Not sure bike brakes get that hot, but brakes on race cars can.)

On a car, drilled brake rotors can help lower rotor temperatures because the pumping vanes of a ventilated disc brake rotor can pull additional airflow through those holes.

That said, most race car rotors are slotted these days, not cross drilled.

Honestly, Probably sand rotors once every few years for myself. But it sure would make production tunes easier without having to sell them a new rotor.

I have tried sanding rotors in the past but I don't really think it does much cuz I don't think you can really take much if any material off

but what you can do is get one of those red sanding discs that you chuck into your drill, put the bike upside down and run the sanding disc against the rotor at a bit of an angle , you can get that rotor spinning pretty fast

I had a new Fat bike with whining/ squeaking/ noisy brakes, I got a shuttle to the top of a very long very steep hill and rode the bike down doing multiple panic stops and it cured the noisy brakes

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Originally Posted by SJG

FWIW I have to resurface (or replace) my rotors around once a year (every 2500mi). They get too polished. They work 3x stronger afterward. MTX Brakes told me to do this periodically to keep performance top notch. I also clean the rotors every 5-6 rides, it's shocking how much junk comes off.

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What is your cleaning procedure? Do you have to rebed the pads after?

I was considering cleaning my rotors every so often with brake clean but then thought it would remove pad material and don’t feel like bedding in pads multiple times a season. Maybe Iso alcohol is a bit less harsh.

I use automotive brake clean and the blue shop towel (lintless).

The initial bedding process transfers pad material to the rotor, then the brakes work great. Brake clean doesn't remove that, so no addl bedding is needed. Really brake bedding takes like 30-60sec of being on the brakes, that's all. Easier on a hill, but can do in 10min on flat ground 3-4sec at a time.

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Originally Posted by east or bust

What is your cleaning procedure? Do you have to rebed the pads after?

I was considering cleaning my rotors every so often with brake clean but then thought it would remove pad material and don’t feel like bedding in pads multiple times a season. Maybe Iso alcohol is a bit less harsh.

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Old school cantilever / v-brake method was to just cut some little rectangles of Scotch-Brite and wedge it between your brake pad and rim. Assume you could do the same with rotors. Rig up a colostomy bag to a drip system of isopropyl and fly down a hill.

Assuming rotors are steel it seems like they should be ground or dressed with a stone, not sandpaper. This is purely from my experience with metal working so I may be completely wrong, I just wouldn't expect sandpaper to be all that effective.

Agreed, that’s why I would be interested in a MUCH more durable abrasive medium.

Cut thin silver off a gummy stone for ski edge. Hall ass down a hill and see what that does?

Definitely on the right track, but I think it would be very, very difficult to cut it 2.2-3.0 mm thick, and figure out how to affix it securely in a caliper.

I thought this was about f-ing around to play with glazed jank? Just supper glue the sandwich cheese slice of gummy stone to old pad.

I'm an idiot, how to slice gummy. Probably band or hack saw and then sand down. The winterstiger gummies are not that hard to cut (gray ones, red probably to soft you.

Riding long steep trails can fuck a rotor. The less of a badass you are, the more you're dragging brake the whole time. And sometimes they just seem fucked out of the gate. Some pad/rotor combos just don't play well together. I've had downhill seasons where I'm cursed with squealing. I've had bed ins that never resulted in quiet stopping. I've had successful bed ins where the brakes started squealing 2-3 runs later. Considering a ballpark average of $160 to replace front & rear pads & rotors, it's hard not to want to fuck around a bit when the rotor's fairly new or the pads still have a lot of meat on them.
I've spent a fuck ton of time sanding pads, soaking pads in alcohol, torching pads with a mini propane torch, sanding rotors while spinning the wheel, sanding rotors by hand to achieve the recommended against the grain rub, sanding rotors with a random orbit sander, cleaning rotors with auto brake cleaner, cleaning rotors with alcohol. It's fucking maddening and a humongous waste of time and energy. And inevitably irritates the fuck out of my arthritic thumbs. So yea, I've got a ton of empathy for rideit on this one and I've also thought about a padset with diamond stone instead of sintered pad material. These things even look like brake pads! https://m.media-amazon.com/images/I/..._AC_SX569_.jpg
Correct me if I'm wrong, but when an auto shop turns brake rotors, they're scoring the rotor in the direction of travel. So why would it be different with bikes?

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Originally Posted by jm2e

Riding long steep trails can fuck a rotor. The less of a badass you are, the more you're dragging brake the whole time. And sometimes they just seem fucked out of the gate. Some pad/rotor combos just don't play well together. I've had downhill seasons where I'm cursed with squealing. I've had bed ins that never resulted in quiet stopping. I've had successful bed ins where the brakes started squealing 2-3 runs later. Considering a ballpark average of $160 to replace front & rear pads & rotors, it's hard not to want to fuck around a bit when the rotor's fairly new or the pads still have a lot of meat on them.
I've spent a fuck ton of time sanding pads, soaking pads in alcohol, torching pads with a mini propane torch, sanding rotors while spinning the wheel, sanding rotors by hand to achieve the recommended against the grain rub, sanding rotors with a random orbit sander, cleaning rotors with auto brake cleaner, cleaning rotors with alcohol. It's fucking maddening and a humongous waste of time and energy. And inevitably irritates the fuck out of my arthritic thumbs. So yea, I've got a ton of empathy for rideit on this one and I've also thought about a padset with diamond stone instead of sintered pad material. These things even look like brake pads! https://m.media-amazon.com/images/I/..._AC_SX569_.jpg
Correct me if I'm wrong, but when an auto shop turns brake rotors, they're scoring the rotor in the direction of travel. So why would it be different with bikes?

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yeah its a lathe like m/c that skims off metal as the disc or drum rotates , you can only take so much material off , the more you take off the thinner/ more easily they overheat and warp again SO I think that was something they did back in the day of big American cars, I beleive they just get replace discs & drums now days

IME sanding discs or pads cleaning with a solvent or brake clean is something to try but I don't find it real satisfying but if it works great

If you havent got any sandpaper taking out the pads and scuffing them on a concrete basement floor works pretty well

I try to give the brakes a break by pumping them to let them cool instead of riding them all the way down

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Originally Posted by jm2e

Riding long steep trails can fuck a rotor. The less of a badass you are, the more you're dragging brake the whole time.

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I feel seen. :D

Honestly, I've had the best luck with just rubbing new pads together under running water and perhaps finishing up the rub with a bit of isopropyl before installation. Typically caliper alignment is a bigger issue for me. I'm intrigued with a gummy Stone idea or just for fun.

Yeah, this is more of an idea to get some more life out of heavily glazed, well used pads and rotors. New bed in is simple.

I do a lot of very steep and long descents (LCC, BCC, Skidders stuff), and do have to de-glaze my pads every 30k' descending or so. A day at Deer Valley can be 15k' descending, so that's every other time. 3-4 sec on a belt sander to remove glaze and they are as good as new.