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not sure why i'm not a fan of sand paper and rotors, i feel they would become uneven and do more harm than good
Well I have access to a high accuracy surface grinder at work, I wonder how I can get it to hold brake rotors.
Your commitment to the cause is notable and commendable!
Magnetic base.
Story time. Ages ago, a good customer at the shop I worked at picked up some fancy aluminum Italian road frame and at the same time a brand new Phil Wood bottom bracket to go with it. He installs it and torques to spec (he was a highly competent home mech and used us when the WTF quotient got outta hand) and goes to tweak the chainline some and lo n behold, bottom bracket is frozen solid. Keep in mind, this is brand new, hasn't had the wheels installed yet much less been on a ride. We're contemplating the hows and decided to call Phil before proceeding with any plans from C on up the alphabet. Good thing we did. The cups and the frame were made from the same grade aluminum and had the same heat treat. This in turn meant the thread surfaces had near identical surface finish/topography, so when the BB was tightened to torque, those high and low surfaces interlocked to each other fast, creating a mechanical seizure between the mating parts. Keep in mind those surfaces would need to be seen under a microscope, you wouldn't see any difference, and the threads were greased properly. So, turns out ours and our customer's ignorance of this material property was at fault, and Phil has cups made from a different alloy strictly for this reason. Thankfully we didn't sell em the wares or that would've been an expensive error.
So what's that got to do with brakes? Simple. Different compounds will have a different 'grit' if you will, be it size, composition, or both. Doubt my claim? Take different grit sandpapers and rub them against each other, grit to grit. Note which ones slide easier and which ones lock up. The same grit sandpaper will damn near be impossible to rub against each other under pressure. The closer you get to the same grit, the more /easier the grit will interlock with each other, their topography matches. If you want the most consistent braking possible, replace with like or be prepared to take an orbital sander to a rotor if you don't want to replace it. Thank you for attending my Ted Talk.
That would require a helluvan aggressive abrasive and muscle. I'm not a fan of sandpaper as I don't know the composition of the adhesive and abrasive and don't want to potentially cause a contamination issue on the rotor surface resulting in poor braking characteristics. I think about how much I clean the metals I TIG when after cutting/grinding and apply the same reasoning to my rotors. Maybe I think too hard on these bits, def a possibility.
How about some good ole (glass) lapping plate and fine lapping compound? Still too much risk of having the compound getting embedded in the rotors?
Rotors are hardened steel -- you're not removing a meaningful amount of material.
That would be overkill and not necessary. The goal is to scuff up the rotor surface so the new pads can deposit themselves quickly, evenly and efficiently. You really don't need fine sanding compounds for this. Nuke it with some 99% ISO or brake clean for added peace of mind. From Hexon's TED talk, we can gather that we want to match the roughness of the pad and rotor for maximum interlocking. Lapping happens naturally when you ride the bike.
Agree that people misinterpret "sanding the rotors" as it's commonly practiced (or at least as I do it). I think of it like taking a brillo pad to a pot - very aggressive cleaning. I'm not trying to really "sand" the rotor. Just take off the most microscopic top layer of pad material and scuff it up enough to remate with new pads.
I never prep my rotors. I just run cheap 2,50 chinese resin pads and they all bite the same. To bed them in more quickly just use a few drops of water.
What you're describing is galling. A situation where a like-for-like metal will basically weld itself in the threads. Some metals are more susceptible to this than others. You can see the effect here:
https://www.youtube.com/watch?v=R54spcBn-Sk
Or here: https://www.youtube.com/watch?v=mHAhfX7iRjs
Or here: https://www.youtube.com/watch?v=jlDUqf-1XsM
The point is, galling is not relevant to brakes. Unless you're trying to use brake pads that are a billet of the same stainless steel that's used for the rotors. Then maybe.
Totally aware, but using it as an example to show why I switch rotors if I switch pad compounds. The like size grit/ grain structure analogy is legit when it comes to the discussion at hand, providing context to what happens between a bedded in rotor and pad set and why simply swapping pad compounds may not provide the desired results. The pad material grabbing at each other as contact made is not significantly dissimilar to what occurs during galling.
Side, that AvE cat is one of our own. Highly entertaining fellow that one.
Hopefully you've all been being careful when performing maintenance on your brakes, but a couple new studies just dropped reinforcing that inhaling brake dust is bad, mmmkay. No types of dust were good for you, but interestingly one study showed that metallics were less damaging than organics when exposing lung tissue to dust. Either way, I'd encourage everyone to clean their stuff using a wet method to avoid dust generation, and ideally catch the majority of the liquid in a garbage can for proper disposal, because if you just let it dry on the floor of your workshop it can get kicked back up if you use the air compressor, sweep, etc...
From: https://particleandfibretoxicology.biomedcentral.com/articles/10.1186/s…
"The scientists examined the effects on lung health of particulate matter from four different types of brake pad with differing chemical compositions; low metallic, semi-metallic, non-asbestos organic and hybrid-ceramic.
Results showed that of the four types of brake pads, non-asbestos organic pads were the most potent at inducing inflammation and other markers of toxicity, and were found to be more toxic to human lung cells than diesel exhaust particles. Ceramic pads were the second most toxic."
And from: https://www.sciencedirect.com/science/article/abs/pii/S0300483X25000113
•Exposure to brake pad particles induced lung inflammation and a tendency towards fibrosis.
•Notable alterations in pulmonary function parameters, indicating compromised respiratory health.
•Significant changes in plasma metabolites, implicating KEGG pathways of purine metabolism and caffeine metabolism.
•Alterations in intestinal microbiota, with implications for the gut-lung axis.
Ok I'll try bring this convo over here and reply to this comment-
I really hate to derail this conversation but I must talk about those maven cups. I've always been a fan of the Shimano overnight cup bleed rubber band thing and I thought these cups would help me do the same things to my mavens.
Needless to say, it did not work, in fact it made my mavens feel terrible. So I've never used them again and suck with syringes. I think having a bit of positive pressure in the system and "overfilling" it a bit by pushing a little bit of oil from the caliper up with the bleed port on the lever closed makes them feel the best.
Though I'd be really interested in your thoughts.
I've never relied on the rubber band to the bar method (now or 20 years ago) - it might help if small air bubbles have been mixed in and trapped in tight corners of the brake but generally I try to flush degassed fluid through the whole system and that carries a lot of the air with it.
Theres 2 things which seem obvious but manufacturer bleed methods seem to forget -
Gravity - air will always travel upwards so if there is a local high point then a vacuum won't be able to pull it unless the path to the bleed port is roughly vertical. Some brakes have more spots to trap air than others so if you're having trouble you might need to experiment with orientation of the whole system*
The reason a vacuum helps is because it changes the ratio of bouyancy vs friction (archimedes principle). Small bubbles have a relatively high surface area compared to their mass so the friction on the bubble prevents them from floating. Pulling a vacuum causes the bubbles to expand, greatly reducing their density and if there are multiple bubbles that can join together they will now be much more likely to travel up to the lever.
Tapping the brake gently also breaks the friction between the hose which helps it get moving, and once moving will be more likely to continue travelling upwards. Too much agitation will break up the bubbles and create a foam which is harder to move though. Personally I like to fill a sysringe and pull a vacuum to degas it before gently pushing it in to the brake from the bottom. That makes for far less air to remove later on. Holding pressure on the bubbles shrinks them and might help it squeeze through small gaps but might not be a lot of help getting it all out.
*I really want a workstand that somehow clamps in the middle of the bike and makes it easy to spin 360 degrees for this exact thing. EVT had an offset clamp on their stand for the reason too, but it held the seatpost which I would like to be able to remove in the stand as well
Yup I do it a very similar way - the the inital bleed nipple opening at the caliper involves drawing the air out, as well as any crud that might be stuck there. I'll often hold the lever closed so its not sucking the bladder back or if you have already installed a cup/top syringe. But leaving the top plug in place works too
And yeah i've had bleed blocks fall out too - I'll always hold it with a pin or rubber band now!
@Digit Bikes mentioned that pulling a vacuum might make the bubble too big for them to be able to move through the hose. I'd say pulling a vacuum with the other syringe opened (there's enough restriction in the line or complete system that there still will be a vacuum) will enable the oil to flow under a vacuum, so pulled through the system, thus the bubbles will enlarge and flow together with the oil.
That's why I was saying here about using a vacuum machine connected to both ends of the brake system with a Y plumbing system and pulling a vacuum on a reservoir then maybe even having a pump or something flowing the oil from the caliper to the lever (and back towards the caliper through the external plumbing) to promote this flow of bubbles. The only reason for this is to a) be able to tune the level of vacuum (0,9 to 0,8 bar absolute pressure, so 0,1 to 0,2 bar vacuum might be enough and prevent ingress of air past the master seals) vs. how you're able to control it with a syringe and to be able to plug the system and have the machine run instead of standing there and handle the two syringes back and forth, pulling vacuum, holding it there, holding your hands up above your head, etc. etc.
Re a work stand clamping in the middle of the bike without using the seat post, could you use the Silca ‘Hirobel Frame Clamp’ or something similar? Seems designed for aero road bikes but a very brief web search shows people using it on mtbs.
The vacuum machine makes me think of the Unior rotor/pad bedding machine. It's a $2,000 piece of equipment to replace pedaling up a hill a few times. But sometimes it's raining, sometimes it's snowing, it takes employees time to go do the pedaling (assuming the shop actually does a bed-in procedure), maybe the shop is located where it's hard to do the bedding procedure.
The vacuum bleeding machine seems similar, although standing there with a syringe in each hand seems like a lot less trouble than bedding in brakes.
Saying all that to ask the industry folks on here if they are seeing or hearing about the Unior machine getting purchased by larger shops. I would think that would be a useful data point on the commercial viability of a vacuum bleeding machine for brakes.
I suppose shops could also use the vacuum machine to get more business be claiming that their brake bleed with the machine is superior to a home bleed with syringes, but I'm not sure I'd buy that argument.
It's actually Sinter's machine, not Uniors. COmpletely different company, but they both sponsored the now defunct team
Apparently they made it to have consistency in bedding in brakes vs. the variability when shop employees pedalled up the hill.
As for better or not, if it frees up a service tech to do other things, any machine will pay itself off VERY quickly if it actually works. As for me asking it, I'd use it at home and I'm just lazy
As someone who went from bleeding shocks by hand to using a vacuum pump about 10 years ago, a brake bleeding and pad bedding machine are 2 things I would immediately buy if I was running a general workshop. The time saved plus consistency (which saves even more time on parts coming back to be redone) is crucial for a sustainable workshop. I only occasionally do brakes but I'm still planning on building more tools for pad bedding when I get the time.
Actually the same goes for wheel building - I used to do about as many wheels as I do shocks but the reason I stopped is I couldn't invest in dedicated machines for both jobs. Look at Wheelworks in Wellington, NZ for the kinds of stuff I mean. https://www.wheelworks.co.nz/?srsltid=AfmBOooE6xOR6S3PT9hMztNxJQiCKBytlFTaQxgyXLGz_M1V2wYOaGln
In my opinion if a shop is hoping to do technical work like brakes, suspension and wheels they absolutely need to invest in modern tools. The productivity rapidly pays for itself, making life better for customers and the workshop more sustainable/profitable. The trend I see is if bleeding brakes is too much of a hassle then a mechanic will convince themselves its "fine" and doesn't need to be done, whereas if the service is super easy you'll be much more likely to get it sorted then and there without much thought
Couldn't a cheap treadmill be used to bed brakes? Sure the size is a bit of an issue in a small shop but it'd get some better use out of them that way instead of as a clothes rack they typically become.
https://www.wheelworks.co.nz/what-makes-us-unique/
Pretty cool read for anyone who's curious. A lot of very expensive, very cool tools and machines.
I hadn't thought of the Hirobel but those are pretty cool - and might actually do a pretty good job. My dream stand would be able to spin an ebike right around the centre of gravity but with shocks and wildly different frame shapes in the way that could be overly ambitious! Might have to get one to try, and possibly use my new 3D printer to make some custom pulleys for different shapes.....
Probably - apparently the motors in treadmills are super robust and torquey so are perfect for re purposing in to stuff like that
IDK about the whole expensive tools necessity spiel. If you have good pitch perception, you can tension wheels like a champ. I understand that an amateur like me has infinite time to fine tune their wheels unlike a shop that has to optimize time budget to make a profit. But like in many other crafts, a talented and skilled wheel builder likely doesn't need fancy technology for superb results.
That makes sense to me. Thanks for taking the time to reply.
If you could wave a magic wand, would the brake bleeding machine also be able to pressurize the system at a consistent and repeatable pressure - like the trick of pressurizing Codes from the bleeding edge fitting at the caliper before closing it off. Sometimes I do end up letting a touch of fluid out of one or the other. I can definitely see the value of doing that consistently and quickly in a shop setting.
Any extra pressure in brakes will go somewhere. Either inflate the bladder (and could cause problems once water is ingested and the volume increases, see option two) or the caliper pistons will push out and advance towards the rotor to take up the slack. The timing of the port will stay the same and the brakes will grab at the same time. Maybe the bite point will be quicker because the pads are advanced more, but you don't need to overfill the system to achieve that, just advance the pistons.
Or get contact point adjust brakes...
When we agree, we agree pretty damn well.
Post a reply to: Nerding out on Brakes shall we? Not another tech deraliment