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I wouldn’t put my 45kg beginner rider wife on those things
Does anyone know if you really have to resurface the rotor after it has been contaminated through the pads, or if a thorough wipedown with isopropyl alcohol should be sufficient?
I ask because I have brand new Hope green pads(that I have bedded in properly) that at least on the front are starting to act as if they are contaminated(my caliper is bone dry and so are the backplates and pad material) so the pads are continuosly skipping across the rotor surface while I'm braking.
I really don't want to dump money into a powertool and all of that now so it would be good to know what really is necessary after a contamination ordeal.
alcohol and sandpaper should do the trick
Hayes Dominion A4 weirdness - looking for advice.
One of my dominions keeps losing bite point. I bled the brake it an the bite point was feeling sharp and where I wanted it, after a couple rides the bite point kept pulling in towards the bars further and further to the point where the lever was pulling all the way into the bar. I did another lever bleed to get the air out of the system, which returned the bite point to perfect. Riding around the parking lot it felt mint. Again on the first ride the bite point completely disappeared. It seems like there is an air gap somewhere into the system, but no brake fluid is coming out of any of the ports or elsewhere. The system seems completely sealed so far as I can tell. Looking for advice - front brake lever pulling into the bar is scary! Thanks
Likely that there is air elsewhere trapped in the system. You may need to do a full bleed instead of just a lever bleed.
Dislikes very pinkbike, it’s a brake nerds thread not a crap brakes, let’s be honest with ourselves
As Jaloypj said, do a full bleed. Also, double check that the hose nut at the lever is fully torqued. When I had them, at least once I thought I had it tightened up enough, but the bleed felt like crap. I put an actual torque wrench to bring it up to whatever value they say, and ended up turning the nut like at least 2 full rotations more, and the problem went away.
Clean the calipers really, really well and make sure they are completely dry. Go ride and inspect afterwords to verify that they are not leaking anywhere. I have both heard and seen that the newer Dominions have been prone to leak which can cause issues similar to a bad bleed even when there is no air in the system. But first make sure that there is no air in the system, full bleed and work the pistons out to make sure nothing is trapped behind them. Hayes has been quite good, from what I have heard with the warranty process if that is the issue, leaking.
https://youtu.be/yKDVB37AOic?si=UjivGrJdZkxmFB-Y Interesting video regarding brembo’s DFM methods for F1 brakes. I’ve heard some anecdotes about how F1 brake fluid is vastly superior to DOT fluid, but after looking at the composition details it’s still poly- glycol ether based fluid, same as DOT. Will try to get my hands on some as I have some connections to a LMP race team with a few Rolex wins.
I have a feeling that as I have theorized, system fluid pressure is key to management of the fluids boil point, and the idea that using phenolic or other thermoplastic inserts are more armchair theory vs having any practical application in high performance applications especially considering that F1 or LMP car brakes operate at temperatures that no mtb brake would ever hit, >800c. I have a few phd chem eng. at work and will have to pick their brains on the idea of localized boiling and if that’s an actual fluid phenomenon that could cause degradation but I have a feeling that the heat flux isn’t high enough to cause that to happen even if the thermodynamics support the idea. Pretty wild to see how little material is used regardless of the forced induction aero being used for brake cooling. Interesting stuff nonetheless.
Would be pretty cool to build a thermal test system to subject heat to pistons and measure the fluid pressure loss based on various line pressures. Based on the fact that most fluids exhibit similar characteristics where as heat increases the inverse of the bulk modulus of the fluid decreases, thus compressibility increases, giving you some sort of predictability in the system response. It wouldn’t be that hard to measure the thermal effect in a system once you a lookup table to account for the density change.
What kind of grit level would be ok for a brake rotor, and does anyone know if my new brakepads now are considered "contaminated" again or if it should work just to do a light surface treatment of the rotor as well as a a quick once over on a sand paper with the pads as well.
I just want the brake to have a consistent bite as it should be, without the "abs" feeling.
If you have a strong degreaser like a foaming one and a clean brush that’s the way to remove contaminants I reckon, we do it all the time at the shop with 100% success, for the rotor
As others have said, redo a fresh bleed and check all the fittings.
It sounds like you have a leak somewhere since as you add pressure during use the levers creep closer to the bar.
I'm talking about if it's possible that the contamination can be embedded into the surface itself together with pad material so one would need to resurface it. If there's just things on top of the surface then isopropyl alcohol should be golden, but as that doesn't fix my issue, then I need another solution and was wondering if someone with that knowledge would be willing to share.
When I bedded in the new pads I did notice this exact behavior but I expected it to go away through some usage, but it simply has not. I bedded in the pads with a speedo as I do every time just to be consistent, and it doesn't look like the pads nor the rotor have been glaced.
Which brake and which bike do you have? A loss like that points to a leak in the system. Possibly the reservoir bladder, possibly the hose. As others have said, check torque on the hose fittings, but there's a quick diagnostic you can do to determine if it's an internal rupture on your hose. Pull the wheel out of the drops and insert a pad spacer. Set the lever up into the bleed position and attach your syringe to the lever without the plunger in it. you'll need to keep that syringe vertical, so you'll need to figure that out. With the syringe vertical, add a bit of fluid to it, maybe a cm or so. Slowly and lightly pull the lever. This is key. If the lever goes to the bar, watch the fluid level in the syringe. and pull it the same way a few more times. If you notice the fluid level is dropping but not returning to the same height, stop pulling the lever. This is indicating you have an internal rupture in your brake line and it needs to be replaced. This is generally not a warrantable condition as it's related to damage, be it form a crash or poor hose routing. Most bikes have routing down pat these days, but I wouldn't say all do, so if it's the rear brake I'd look where you could make the hose arc smoother.
If the lever is going to the bar but the fluid level is maintaining volume, that indicates a MC piston seal failure. Warranty that bugger.
If the lever firms up, I would inspect the bladder. I've seen brands develop slight tears at the seal surface that would not allow fluid to leak but in use would allow the res to ingest a smidge of air or overzealous syringe use causing the diaphragm to pop out of its sealing surface resulting in the same slow air ingestion.
I've used every grit from 80 to 400. Even a coarse scotchbrite pad.
But I think 240 is the sweet spot for the rotors. Followed by a wipe down with IPA.
Pads, I rub together in the sink under soapy water. Followed by rubbing them together under clean running water.
Super curious about today's BOTD brake set up. Maven calipers matched to Lewis levers. Say what you will about Lewis, but their levers feel really good. Very light and smooth. I'd definitely be interested to see how much of a faff it was pairing them, or if it went pretty smoothly.
I have had a much better success rate using a stiff bristle brush with dawn dish soap on rotors then anything else. Spray the rotor down with water, scrub away, spray down with water to clean, let air dry. I cannot recall the last time I have scuffed/sanded a rotor.
Pads can be hit or miss salvaging, I have found that once Shimano OEM pads are contaminated they are basically garbage. However, I use drywall screen sandpaper to scuff glazed pads. Aftermarket pads that have paint on the edges of the pad material get scuffed prior to installation. I also use Marshy's method of watering new pads, rubbing them together until they have a bit of a rough feeling and washing them off.
When cleaning contaminated rotors I boil a pan of water and dish soap on the hob (use an old pan, or feel the wrath of your partner) and leave the rotor in there a few mins bubbling away. Got the tip from the yeti race team mechanic years ago.
When you say another bleed to get air out of the system, did you actually pull air out? Or was it just a general term?
If you are sure sure sure there is no more air while doing a bleed and then you have air in the system the next time you bleed, you have a leak somewhere. I'd do the things others have mentioned.
Regarding the nut, thanks for that one, I have code rscs that seem to be pulling some air slowly (also have a wandering bite point a while after a bleed) and is for sure a very easy thing to check. The old set I had (that GF uses) still functions flawlessly and it's been in use since 2019, had two bleeds and then a full rebuild in 2024.
The 800degC temp is the rotor to pad contact. They make sure to both keep them warm enough but at the same time have enough cooling. As you can see in the video, they take away everything from the caliper they can. This is for weight savings (unsprung mass and all) bu to also bring the fluid as close as possible to the cooling air. So much so they have cooling fins, ribs and barbs to ensure the caliper itself is cooled. So caliper and by extension oil is cooled, pad and rotor cooled, but kept warm enough.
As for System pressures and boiling prevention, all is fine and well as long as you have said pressure. QED PWR nuclear reactors where water is under 150 bar to prevent boiling at 350°C. But as soon as you take away the pressure, the fluid will boil. With brakes that happens every time you let off them.
Not Mavens, but I'm using Lewis masters paired with Magura calipers. I'd been intrigued about eeking more power out of the stock LH4 I was initially using. The LH4 caliper uses 17 & 14 mm pistons, so I gained quite a bit with the quad 17 mm pistons in the Magura
I was thinking about pairing them with a Cura 4 caliper or a Maven base caliper, but was unsure if the 18 mm pistons would mean I'd have too much lever throw before the pads would contact and didn't want to risk it. Plus I found the Magura calipers for cheap
My Lewgura set up has more throw than stock, but the power bump more than makes up for it, they have immense power and a really nice light lever feel
I did a few full circle passes with 240 grit paper today and it didn't change anything sadly. As this skipping shenanigans happened only in the front, I decided to just swop the front and rear pads just as an experiment. It actually works better, so I simply feel it has to be something with the pads I purchased that just want to be weird. At this point I'm just going to leave it at that.
If it works, don't fix it... 🙈
Getting some pretty horrendous pad rattle coming from my shigura brakes - have been running the same setup for ~18 months now but it’s only been over the last 3 months or so that I’ve been getting it since buying a fresh set for a new bike.
Using Galfer pro pads (which I’ve always used) - wonder if I’ve got a bad batch in terms of tolerances or the backing material isn’t working well with the magnetic piston?
Either way it’s driving me mental, brand new bikes with new brakes sounding like a filing cabinet being pushed off a cliff through any sort of rough corner. In a straight line it’s not quite as bad.
Anything I can try before just buying mavens?
trickstuff power or sinter pads, one piece per side rather than 4, never had any issue or noise with either
This seems to be a galfer thing with their springs. Try bending the tangs of the pad spring into the sides of the pads so that they're held more tightly in place I.e. "preloading" the pad spring. Just be careful to keep the tangs flat with the pad backing and stop them sticking out into the rotors when the pads wear down.
I usually do this before fitting new pads as the rattle drives me nuts if I don't.
The galfer pads are often a little bit short in the length department, They rattle Bad in shimano's and gets worse as it wears the caliper.
Opening the spring helps alot.
It's for a magura brake unfortunately so there's no spring involved, just magnets!
Will try the one piece trickstuff pads
Some detailed shots of the new Hope Evo brakes in this build video.
Hey hey folks, having an interesting conundrum with my Hope T4 V4's and am interested to see if any of you have had similar issues. I picked up my set last August and had run them without complaint until the other week when my front lever started pulling much farther into the bar about 2 minutes into a mild descent. I inspected the brakes and couldn't find any sign of fluid leaks or anything of the sort. I subsequently performed a gravity bleed and had the brakes feeling new again. Next ride, exact same issue! At this point, I was sure there had to be a leak somewhere, so, rebled them and strapped the lever to the bar to pressure test overnight and sure enough, they held perfect pressure. I did notice that when I opened the reservoir to bleed them after the rides, they did seem to be down a small amount of fluid and I was also able to "pump" them back up to a normal feeling (similar to Shimano's wandering bite problem). My conclusion is that there must be a leak somewhere in the system, just not exactly sure how to deduce that problem yet. I think it must be up at the lever as the pads and rotors are not being contaminated, but I can't see any signs of leakage. Let me know what you guys think.
FYI: I have checked the torque and fitting of all the barbs/olives and brake hose fittings, definitely not the issue
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