so my GFs bike with SRAM DB8s was developing sticky pistons. not surprising, i thought, given its been ridden.
but i recently had G2s go under warranty so I ended up buying DB6s as an emergency to salvage a bike trip. worked fine. but, they also developed sticky piston despite being brand new brakes (installed by bike shop) with basically 1-2 rides on em.
looked at the front caliper this morning and they definitely stick out more than one would like. gave them the ol cleaning with the pads out. got the pistons to sit all the way in. pulled evenly and returned. looked good and clean. threw the pads back in. put the wheel on and saw good spacing, felt good. on first proper pull the pads are right back to getting stuck out...
again new brakes, but either the pistons are so grimey deeper on the piston wall that theyre still sticky unless i damn near pop them all the way out to clean... or i'm just approaching this wrong.
i hate that it looks perfect on install, lots of space rotor in the middle no rub... and then the first pull after install you get that spongy to the grip pull until the brake resets, and thats where my problem starts. is there a way to avoid that? or is that inevitable having re-mounted/reset the wheel?
i feel like i'm missing a crucial step between re-installing the wheel... and the first usage of the brakes/pull of the levers. such that i can retain that initial spacing to avoid rotor rub. (or SRAM DB8s/DB6s are just SUCH garbage I should rip them off both bikes, but otherwise they've seemed fine so i dunno)
Have you tried a piston massage (or several piston massages)? I talked with SRAM's Chris Mandell about this for my DB8 review, and it was really helpful for me to understand what exactly it's for. I thought piston massages were about purging air bubbles, but apparently it's exclusively for reseting "piston/seal friction coefficients." I'm still not exactly clear on how a piston massage accomplishes that, but that's what the man from SRAM said, straight from the source.
My best guess is that the high pressure squeeze on hyper-extended pistons helps evenly coat or re-coat the outer ring of each piston seal with oil, whereas those seals can be starved of lubrication otherwise. Seals with unequal oil will create pistons with unequal resistance, which will result in some stickier pistons and some smoother ones.
Anyway, the piston massage spacer is $4, so I'd try that first. And you don't even have to crack the brake open to do it, just pull the pads and let it rip.
Sorry in advance for the ridiculously long response, this is the section from the article: https://www.vitalmtb.com/product/guide/hydraulic-disc-brakes/sram/db8-59421#product-reviews-607871
"So what exactly does the piston massage do? According to SRAM's Mandell, "It isn't purging air, and despite what some people say, it shouldn't be pushing air bubbles out if you have a good bleed. If a piston massage does push air bubbles out of the caliper, that's a sign it wasn't a good bleed." Mandell said the piston massage is "intended to reset the friction coefficient of the square-shaped rubber piston seals in the caliper." Those square rubber seals in the caliper serve two distinct purposes: they need to be slippery enough to slide in certain situations and sticky enough not to slide in other situations. Surprisingly, when you pull your brake lever during a normal braking event, the pistons don't slide through the caliper seals. Instead, the seals stay firmly in place on the pistons, gripping the pistons as they bend and twist in place to allow the pistons to extend. Once extended and twisted out of their natural shape, those square rubber seals want to snap back to a neutral position. It's this elastic spring force in the seal that provides the rebound mechanism in your brake system, not the vacuum from brake fluid. However, those square seals need to stay slippery enough to allow the pistons to occasionally advance in position as your brake pads gradually wear down and get thinner over time. SRAM chose the seal shape and material to provide a very specific rebound force for the brake, and the surface treatment of the piston, seal friction, and tolerances are scientifically tested and selected to create a very specific coefficient of friction. These tight design parameters are also why SRAM recommends using only Maxima Mineral Oil Brake Fluid.
Over time and after extensive use, and sometimes even as brand-new brakes sit in a hot sun-baked container for a month on their way across the Pacific Ocean, the square seals can develop unequal amounts of friction, leading to uneven piston activity when you pull the brakes and a vague feel at the lever. This is where the piston massage comes in. By cycling lots of fluid through the caliper and hyperextending the pistons, the massage procedure helps reset the piston/seal interface, restoring caliper function and lever feel. According to Mandell, this massage step is good to do when you replace brake pads, but he says it's a great thing to do every time you bleed the brakes, and even when your brakes are new. Simply put, "the piston massage is integral for getting the most out of the SRAM mineral oil bleed process." He even does the piston massage on his old Code now, even though the massage procedure was never officially recommended for that brake. You don't need to open the system or rebleed the brakes to do this step, so there's not much stopping you. Using the new 3.8mm piston massage spacer, it's about a five-minute job per brake."
Yep. I did a little bit of piston exercising during the cleaning, but like... How long would these things need to be massaged to work better? lol
One of my issues is the spacer I got is too big so I ended up just using tire levers to achieve the same result... But uhhh can I ride over to your place and steal your spacer tool real quick? I gotta summit trip this weekend and I'd love to not roach my rotor with these lazy calipers. Not sure if I'll get a spacer shipped in before Friday.
You can borrow the piston spacer for sure. Hell, you can borrow my set of DB8's from the test if you need to, for the weekend. I suspect you'll be able to get your brakes working well. I've had a hell of a time getting SRAM mineral oil rear brakes feeling consistently firm, and have worked out a system that I can bore you with when you pick up the pad spacer.
Noice. Imma text ya. Doin laundry right meow.
But ya I need to chew the fat with ya on what process you used. Cuz I'm still worried I might be missing something crucial in terms of like... Literally just re-mounting and getting the lever pulling against the rotor nicely. But that said never had this issue with my Shimanos in the past sooo :/
I've also never had this sort of trouble with Shimano brakes. It's been really hard for me to find a good consistent bleed technique for all three SRAM mineral oil brakes I've had so far (Maven Ult, DB8, and Maven Base). Weirdly it's only been a problem on the rear brake, though. The fronts have all been great, first time.
I think it has to do with gravity and bubbles sticking around in the lines or the caliper, which is only solved by having the brake hose significantly sloped upwards from the caliper to the lever, ideally with the caliper vertical as well, with the caliper bleed port at the extreme bottom. I've only had luck when I got the rear brake line nearly vertical in a stand, which is a huge PITA with internal cable routing (BOOOOOO!!!!!). Also makes me never want to switch brakes, because it's such a pain in the butt to get a good bleed and then you 1) lose your good bleed on the rear brake you're taking off, and 2) have to start from scratch with a new bleed on the new rear brake.
Well my rear has been fine (knock on wood) and we'll be looking at the front today lol. So... Let's see what I'm missing.
Given that they were just emergency DB6s to salvage a planned bike trip (as G2s were under warranty for failure, that did cause a crash)... I don't mind throwin these away or just sellin em to a hardtail upgrader.
I just wasn't gonna be able to ship MT520s/deores in time. But now I regret the whole scenario. Guess I coulda just rented a bike.
IME you can use a stack of quarters (3 iirc) as spacers, tape them together to make them easier to hold... (Pretty sure this is a Calvin Jones trick).
Ya I was puzzling out what to do about this issue, particularly since tire levers are not straight/flat surfaces.
Luckily I live in the best timeline and TEAM ROBOT had me over to literally teach me how to do it top to bottom, let me borrow his SRAM spacer specific for the task, and then finish it off with cutting my bars for me lol
Sometimes it pays to spend all day posting nonsense in Vital forums. What can I say, I'm lucky.
Heck yeah, go @TEAMROBOT !
In case other people aren't as lucky to live close to Charlie, this guy makes pretty nifty 3d-printed blocks too, I've bought stuff from him and it's all worked very well: https://www.etsy.com/listing/1901682137/brake-maintenance-blocks-the-un…
I made my pad massager out of an old 160 rotor. Hack saw’d it in half and got some bolts from hardware sales. Beats my old one which was just a shimano bleed block that a buddy took to a grinder.
When my pistons are all the way out I clean them with qtips. Once there as clean as I have patience for I take a qtip with brake fluid on it and coat the piston.
I used to just call this piston advancing but now sram probably has a patten on piston massage. When you do this really squeeze hard once your pads hit your spacer. I find this helps.
This next part is dirty, but when I put my pads in, if one piston is being lazy and not moving as much as the others, I have a small shim that I can put between my pad and the piston. I put it on the side that is moving too much to prevent it from pushing too far out. Once the lazy piston is in the right spot I remove the shim. Then I go bed the pads in and the heat normally gets the lazy piston moving good.
I 100% agree with this.
I never had any issues with bleeding countless SRAM Code RSC's (dot), and really liked them for how easy and consistent the bleed process was to make them feel great. I now have Mavens and can't seem to get the rear feeling good no matter what I try. I've tried countless bleeds, new hoses, new lever, and various methods, to try purge any air in the system out. It's always the first pull that the lever pull's in further then I'd like, then 'pumps' up to better bite point? Guessing this is the piston seal bedding in more as they start moving under force?. My front brake however has never had this issue and has felt crispy and consistent the entire time I've had the brakes (since the maven launch early 2024).
I will admit I have only been doing the, let's call it the basic piston massage, keeping pads in and using the supplied pad spreader, highlighted in the end of this video. So I will be trying the newer tool and more advanced piston massage to see if this improves the rear bite point.
Silly question, but I can't tell from the original post - are you manually centering the pistons when setting them up after a bleed? One side will always extend faster than the other. With the pads and wheel installed, I use a small screwdriver to push the eager pistons on one side back in to let the other side evenly extend.
I had a SRAM mech advise me to extend the pistons and put a few drops of brake fluid around where the piston goes into the caliper, then perform the piston massage. Use the correct type of oil for the system and be sure to clean up any oil with some IPA after recompressing the pistons to not contaminate the pads (SUPER IMPORTANT). This was from back in the pre-Maven CODE era.
I've revived some super crusty, unevenly actuating brakes with this lube technique. It's likely not officially recommended due to the possibility of contaminating the pads without thorough cleanup after. Makes sense to lubricate both sides of the seals IMO.
With Mavens, the black pad spacer that comes with them is designed to work as a centralizer with the pads in. Pads in, thin side of the spacer between them, and there are 2 wings that extend out into the notch in the caliper. Another reason not to skip on the piston massage (using this piece) after a bleed, it gets the pistons advanced nice & even.
https://www.birzman.com/products_2.php?uID=2&cID=4&Key=386
This thing has been a god send. Just makes doing brake maintence so much easier. Yeah the cut out blocks work. But I love a purpose built tool.
Cut out block I bought didn't fit
not sure anyone made one specific for the DB models.
But luckily for me Robot lent me his official SRAM block so I just access all pistons at once, at the perfect limit.
(sadly, the brakes are barely improving lol... i dunno this is my first year being a 'SRAM customer' and i may describe the process as grueling. GX runs like a top tho so thats fine)
That's quite clever/tidy. I'm sure someone could make their own with the right dimensions too.
Didn't know this, but it makes perfect sense. I will do this every time now.
This tool is also great to know about.
I suppose since this thread is about finding solutions, I should mention what I'd done and talked about with Robot.
So even with the massager and cleaning and what not, the DB8s (not the DB6s) are REAL sluggish on one side. And I was making the issue worse, kinda, as predicted) with that first lever pull being so confident.
There is a video of a guy on youtube using a screwdriver to hold back the normal side to allow the sluggish side to catch up.
I didn't want to try that specifically yet so what I did was just FEATHER the lever over and over. Like 1% more at a time. And let the sluggish side catch up to the normal side. Once they were matched up in spacing, THEN go for the confident pull against the rotor.
While I wish there was a bit more spacing and free movement of the pistons in general, this is at least allowing me to ride with these brakes without roaching my rotors.
I'm just worried it's going to be a 'forever' issue and will probably just swap them out eventually. But I at least got the process down for now, and can buy my own 4$ spacer and get this done easily when I have issues. Exercise the pistons on the spacer, probly give them lil cleaning while they are out, push em back in, pads in, wheel on, feather the lever over and over until pistons match up in extension, then pull hard on the rotor. Done and done. (As long as it's not a bleed issue and I have to chase air bubbles for the rest of my life... I'd rather go back to brakeless BMX than do that lol)
https://www.etsy.com/listing/1901682137/brake-maintenance-blocks-the-un…
Thanks, but they don't have a Maven one.
Nice tools posted.
Turns out the yellow plastic pedros tire levers are just the right size and shape to push one piston out on Codes. Seems like I have to clean the pistons about once a year to keep them running optimally.
Doesn’t TRP and Shimano 4 piston use same size blocks? Looking at Etsy link wondering why there are two different ones.
Something like that birzman tool is great for advancing 1 sticky piston - or take a regular bleed block and cut 1 section out of it so it holds back all but one piston. Do each piston 1 at a time and then when you push them back, make sure they go fully back out in to the bores. You might need a plastic tyre lever to force them right back in there. I think sometimes the square seal design works both ways - when you push them out the seal flexes and gradually pulls them back in, so if you get them completely topped out they are more likely to fully "reset".
You can also give my friends at Radic a dollar (NZ, which is like 10 US cents) and 3d print their version https://www.radicperformance.com/store/p/heavy-duty-bleed-block-3d-stl-file-only-l64mh?srsltid=AfmBOoqFCfJvoqx4-X06xadTK_dxLRO7v1Xr1yPdlEY68_75BiSZx8rr
I'm liking the sram tool that lets them all out at once (and you can still visibly see which ones are sluggish). It seems like, knowing there brakes are a faff, they took more of a hammer approach to piston block rather than scalpel. And they basically say to pop em in and out over and over again with the tool, seemingly implying they need to be 'broken in'.
I've also found it great for getting max piston access and just cleaning them all at once. To me it's clear part of my limiting factor is my work space and how it affects my ability to actuate the brakes and what not to re-set them. Once installed, I have to flip the bike right side up to get better piston actuation with each minor lever pull... And slowly work my way towards all pistons coming out matched up and then pull harder against the rotor.
I've yet to resort to the screwdriver trick from youtube, as I'm kinda doing a gentler method of the same idea of allowing the sluggish side to 'catch up'. But if this problem immediately comes back its straight to the screwdriver and after that straight to the bike store to get different brakes. As this is ridiculous. Never experienced this before lol
Or you can download this one I made for free: Shimano 4 Pot Piston Pusher by askingforafriend | Download free STL model | Printables.com
I found this one on printables in NZ - The guy made it for me.
Shimano 4 piston cleaning block | Download free STL model | Printables.com
Theres so many on printables though, here anther:
Shimano Saint / Zee piston cleaning block | Download free STL model | Printables.com
I wonder if we should go back to two pistons, that are just much bigger?
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