Nerding out on Brakes shall we? Not another tech deraliment

Yes I’ve used adapters. Nothing wrong with them but it makes installing slightly more faffy.

I haven’t used centerlock adapters with magura 220mm rotors. I won’t consider rotors from unknown manufacturers like sumart or other shit like that. Aside from hope vented rotors (which are too thick to work and also don’t fit the adapters), the mdr-p’s are one of the thickest rotors I know but they don’t make the 220mm in centerlock.

BCA makes a 2.4mm 6-bolt rotor which I could use with an adapter but I haven’t tried them (yet).

Kiitos AnttiH for your replies.

Has anyone tested the effects of fully cleaning the Shimano phenolic pistons? Is using compressed air the safest method to remove the pistons?

Cleaning pistons is good general maintenance and makes a difference in the seal longevity and helps clear up the bores of any material that might lead to corrosion build up, but I'd just go ahead and order one of the aftermarket rebuild kits on Amazon/Ali and swap the pistons and seals out. Then you'll be well able to clean the piston pockets, ensuring less likelihood of corrosion build up. Those kits work well enough and are cost effective, so if you're going to disassemble a caliper you may as well rebuild it with fresh seals and pistons. Air compressor works a peach to pop the pistons. Blow in from the hose port or caliper bleeder port and make sure to wrap the caliper in a rag prior to doing so. 

Yeah man, I don't know what I was thinking! I have seen brakes that have little signs of fluid weeping from the vent hole in the membrane cover, and I had thought some manufacturers might have been incorporating a sort of pressure relief hole into the rubber membrane. On further consideration, I guess they all probably just had membrane failures, or weren't' tightened evenly such that fluid could work its way around to the air vent hole in the cover. 

It's just water/moisture getting pushed out from above the membrane. It's normal. 

Or fluid that might have gotten in there from messy bleeding or that has seeped through the membrane.

Have anyone tested pads from Sixpack racing?

They are quite a bit cheaper then Magura or Galfer pads. And as stated earlier in this thread, that when pads get contaminated they are impossible the get back to top performance, a cheaper but decent pad alternative would be good.

MTB Brake Pads | Semi, sinter, organic | Sixpack Racing

Got a reply from Taylor.

Long story short, he said that it’s normal that the brakes don’t hold a vacuum due to the design of the piston seals.

This is the first time I’ve had this with any brake but I got a relatively good bleed by cycling fluid back and forth and then bleeding the lever with a cup. I kept the lever depressed for 30mins and then pumped it to get any residual air out (there wasn’t any). But that seemed to lessen the pump up.

My dumb ass did that thing where I drink tequila and go online shopping… anyhow I bought a pair of these before thoroughly reading (and being thoroughly unimpressed with) the specs. I guess I’ll decide if they finally arrive whether they’re worth running or not. Currently on Hayes Dominions and they’ve been my favorite brakes as of late, Magura MT7s were ok but had some issues I wasn’t super happy with but I was able to finally get a good bleed on them after much trial and error. 

They are probably made by Galfer as apparently they have euro Manufacturing 

Crosspost from another forum but I find the information interesting:
https://www.emtb-news.de/forum/threads/bremsscheiben-design-vs-funktion.11971/

Tirolbiker63 seems to be on the topic. I'm not sure if he posts here either.

My finding from here was that Intend 220m 2,3mm or Brakestuff discs would be quite okay upgrade to my current Shimano Saint with 203mm icetech rotors.

Anyone have solutions to pad/retainer clip rattle for your Hayes Dominions?

Just expand the pad spring out more before installing? That's all I do and never had rattling.

Any (real) idea why one side of the Saint master piston looks like it has been scratching itself to the point that the surface looks matte? The other side looks more glossy and normal.

It's being pushed to one side by the lever mechanism. The lever is not acting perfectly axialy but at a bit of an angle. I suppose. 

FYI: Trickstuff finally released a high quality English bleeding videos https://www.youtube.com/@trickstuffgmbh It is good to see the extra caliper bleed step in video format.

As Primoz just said, clearly its being sideloaded. In addition to that, it might have to do with the surface finish on the inside of the master cylinder body. In the huge volume of discussion of the Shimano wandering bite point phenomenon, I saw it pointed out that Shimano master cylinder bodies are bare aluminum, while the claim was made that other more boutique brakes like Hopes are hard anodized after the master cylinder is bored, so they have a smoother internal surface. I could imagine that after a lot of cycles, especially if there is any oxidation that has formed, the Shimano may offer a significantly more abrasive surface.

Exactly. Watch how the push rod articulates through the stroke. There's a sudden direction change. If the ball joint interface between the pushrod and piston bind up, that piston is getting loaded incorrectly and won't travel parallel through the bore. 

Has anyone thought (in theory atleast) about modifying a motorcycle brake master cylinder, like a Brembo or equivalent, for use on a downhill bike? What issues, aside from handlebar radius and the large brake fluid reservoir, might arise?

Main issue would be your friends making motorbike noises at you on every group ride 

FWIW, in the pre silver/bronze Code days RSC was anodized while everything under it was not. Doing a bleed rsc has clear fluid even after two years while lesser models have a very dirty fluid due to wear of the aluminum bore and suspending the particles in the fluid because of it. 

Thanks for that tidbit @Primoz, that's quite interesting!

No probs, happy to share. 

FWIW, I don't know how it's handled in the current Bronze & co days, haven't had my hands on any of the newer brakes. The situation I described (RSC anodized, R(S) and lower not) applies to Guide and G2 brakes too. And the reason for the difference is that with RSC (and Ultimate) brakes both the master and the caliper are anodized after all the machining, so anodized inside and out. Lower tiers are painted on the other hand and are obviously painted only on the outside. 

Could this be one part of the equation that makes green Shimano brake fluid go dark together with dirt from slave pistons? I cleaned and checked the actual bore and there's no sign of wear. If the piston would be metallic instead of plastic I guess there could be signs of wear. This could be case with aftermarket titanium etc. pistons.

I'd say yes. DOT fluid is translucent amber and with painted brakes becomes opaque (non-transparent) grey-ish if they are used. If the brakes sit unused for a long period of time this does not happen, ergo it looks like it comes from bore and piston wear.

Yeah, aftermarket titanium/alloy pistons from AliExpress are obviously a great idea when you take all this info into account
There's a reason Lewis for example does PEEK pistons - hard, stable, chemically stable. Maybe a bit hard (PEEK is often used as a counterpart material to steel when it comes to gears to make them quieter). Trickstuff does POM (Delrin) and Igus has an article Piccola uses (used?) one of their bearing grade (plastic) materials.

Tried those Ti MC pistons when the ones on an old set of SLX brakes went and crapped out. No good. They were undersized and rocked enough in the bore during use to allow the primary seal to lose seal, I.E. lever go straight to the bar. Unfun to learn to say the least. Had high hopes since the alloy ones I used to replace the plastic Sram jobbers in his Levels worked a peach. 

Careful there, PEEK, PAEK, and PEKK are not replacements for any alloy steel or SS. Compressive strength of any of the PEEK materials in the family is between 13-18KSI in a neat form, no glass or carbon fill and generally will not ever be over 25KSI without significant carbon fiber loading. PEEK is one of the most expensive thermoplastics, and while it does have very good chemical resistance to solvents and heated solvent vapors it by no means is it a mechanical replacement for Aluminum or steel. Its also a PITA to machine, and sucks to mold as tool temps under 300°C will result in an amorphous material with severely reduced mechanical properties, on the flip side molding clear PEEK is pretty cool... All these plastics will suffer in the sense of CTE. Just doing some quick math a 60° increase in piston temp with PEEK would result in diametrical growth of about 55µm or .002". That might seem like nothing, but I have a hard time believing that it wouldn't have some effect on brake feel due to the extra compression on the piston seal. 

I never said it's a replacement. I said PEEK is used as a counterpart material to steel in gears. Meaning one gear is steel, the other is PEEK. I'm not an expert in geartrain design and obviously you don't see PEEK gears in car transmissions and the like, but I did hear a steel/PEEK combo has been used in an eBike drive unit to quite things down, which is the role PEEK plays - use it where you need a quiet geartrain but also need more strength in gear the usual plastic materials give you. COnsidering you don't see aluminium gears, there must be something on PEEK that gives it an advantage, I'd bet it would be surface hardness or something along those lines.

Considering this (PEEK being used to pair to steel gears) while aluminium is neve used for gears, I said PEEK might be a bit hard, i.e. used as a brake master piston it might scratch up the bore too, just like a steel, titannium or probably even aluminium piston would. But I don't have any experience with it and it might be empty worries...

As for CTE, if that is an issue that arises with a master cylinder in the brake, there are bigger issues than CTE itself... With the way seals are done on a master piston, there should be quite a bit of clearance radially between the bore and the piston, shown by pistons being scratched on only one side. One exception here is Sram's piston selling and jamming, but year... In either case, POM is also used as a master piston material from what I've seen and the CTE of it is about twice as big as PEEK's. If CTE was an issue, everybody would be using aluminium pistons anyway...

PEEK is indeed quite hard, and yes can (and indeed does) scratch up materials that would be perceived to be harder. One example in my line of work is desalination plant HP pumps that use PEEK for the casing wear rings. These definitely do scratch up the corresponding impeller wear rings that are made from super duplex.