« Back to Archive

Hydrolic brake maintenance (Shimano BK-M355)

So, it's a long week-end. I offered to work on my wife's bike. The brake pads were worn down and I offered to replace them. It dawned on me that the brakes were hydrolic. I did not know that. [insert comment re the importance of communication in a relationship]. I do have a bike with discs, but they're mechanical: easy to maintain. But, hey, it's pads. Anyway, I got what I thought were the right pads (B01S). But they're too big to fit into the space. No prob; there's probably an adjustment, somewhere. I look up the manual (which is when I discover the hydrolic thing). I double check the bike. Yup, that's a hydrolic cable. And there's a reservoir thingie up at the handlebar. Damn. I thought those things always came with batteries and flashing lights... I start reading the manual. It's scary. Especially the part about bleeding the system and being sure to use the apparently toxic (and Shimano approved) mineral oil. I use mineral oil to recondition the (wood) cutting boards in the kitchen. It's USP approved... but maybe not for bikes. I digress. All I really needed to do is to get some new pads installed. So, two questions:
  • Why can't I get the new (beefier) pads into the caliber (they do look too big). Is it just fiddling with random screws? {yes, yes, I pushed the pistons back in.}
  • Is this really some kind of complicated thing that only an LBS can possibly handle? Say it ain't so.
By tomorrow night that bike needs to be whole; Tuesday is a workday. If it isn't I am so truly deeply in trouble.
2018-09-02 18:46:19
Hydraulic is the correct way to spell that. I have hydraulic brakes as well, but I do not know how to change pads or add oil.
2018-09-02 19:47:04
Yeah, 'hydrolic' is wrong. But the spell corrector in my browser kept suggesting 'hydroponic'. Which even I am pretty sure is incorrect. I guess A.I. still has a long way to go (context is key!) But, hey, relax. It's a holiday week-end. Give me a break. (But, you know, maybe we should ideate hydroponic brake systems? There just might be something to it...)
2018-09-02 20:12:45
LOL, What about hydroponic bicycles that you can ride underwater?
2018-09-02 21:08:43
What about this? Looks simple and you don't need to touch the fluid. I'm wondering if you didn't push the pistons back in?
2018-09-02 21:12:22
Oh. Just read that you pushed the pistons. Are you sure you have the right pads? Ibet that's the problem.
2018-09-02 21:21:21
Replacing pads is really easy and doesn't involve lots of steps. If they don't fit you have the wrong size. Shimano pads, the "official ones,"  with metal, require a Shimano rotor. I'll bet you have the resin pads but bought the official Shimano pads. Consult your LBS.
2018-09-02 22:55:35
Just asking for clarification as I have the same setup. Where would he have gotten rsein ones go begin with, or does Shimano make some with resin and some with metal?
2018-09-03 09:49:01

This is from a conversation with Frank at BikeTek, my LBS. They have to open up the brakes to see what kind you're using, generally. I'm assuming Ahlir thought, "ooh Shimano brakes," and got the wrong kind. Less high-end bikes use SRAM rotors and resin pads.
2018-09-03 11:24:04
I got it now.   I guess the best thing to do is to look on the website for the bike manufacturer to see exactly what type of brakes you have and what the replacement parts are. I have a Trek and I've emailed them a few times about replacement parts and they give me the exact model #.
2018-09-03 11:52:56
Ahh... what a night away from the garage can do. This problem was obvious this morning: I had not pushed the pistons in far enough (or maybe I just hallucinated doing it). I had to confront the fact that working on a bike on +80°F weather on a humid day is maybe not the ideal, and it does affect my judgement. Good to know. I did have the right pads (B01S) for the caliper (BK-M355). I got them from the Amazon. I got the resin ones just because. I usually use sintered ones. Once I pushed the pistons in properly, the pads took 5-10 sec to install. To all who responded with suggestion: Thank you! I'm sorry to have had to vent in public.
2018-09-03 13:49:59
That's ok. I learned that changing my disc brake pads is super easy. I didn't know how to do it before, so this saved me a lot of$$$
2018-09-03 14:43:52
@Ahlir,  if it makes you feel any better,,, I spent Friday afternoon installing new brake pads on the SO's automobile only to discover that one of the caliper pistons was frozen.  So I had to install the new pads temporarily so I could pick up a caliper rebuild kit from the parts store.  The guy at the store was real surprised when I asked for the rebuild kit  - 'wow! doing it old school' he says.  Apparently most shops just replace the whole unit instead of replacing the internal seals.  But the seals were only six bucks instead of over forty for the new unit.  My labor is cheap....  it was a fun day.    
2018-09-03 14:50:45
Again, apologies for my intemperate intrusion... I put the wheel back on but then discovered that the brake was just not working right . (Botttoming out the lever stops the wheel, sort of, on the stand. Maybe it's time for bleeding the system? (And, in retrosect, maybe part of the reason in the first place that the brake didn't seem to be working all that well). Back to the YouTube. After watching three versions of the bleeding process, I feel confident that I know what to do (hah). I order up a kit on the Amazon. Only a couple of days. (I hope that the front brake keeps braking.) Hey, I notice that I'm connected to the interwebs... Suddenly I feel an urge to check up on alibabaexpress; my preferred source of bicycle bling. Purple tube caps. Check! (My blue ones don't match my purple cable ends. But for 0.93$, what's the big deal?) Blue presta stems! (I asked for advice: I was told they would go fine with purple caps.) And, besides, I have a tube with a bent stem. So it's, uh, a legit purchase. Labor Day (as opposed to May 1st) is a shopping holiday. Some establishments have the decency to give their workers the day off. But only some. I'm happy that I could spend the day doing bike things, including buying stuff, some of which was not necessary (though it was, per the point of the holiday as celebrated).
2018-09-03 19:33:45
Yeah, I always wondered how I can buy something small like bike lights or pedal extenders from china and have them shipped to me for less than $10, but I can barely ship those items to a friend in Philly for what I paid to have them sent around the world.
2018-09-04 12:46:11
I bought a pair of bike lights about 8 years ago. $2.89 total, shipped from Hong Kong. I wonder if we'll see a major company like Amazon take advantage, putting a warehouse in China, say, and using it for certain US shipments.
2018-09-05 05:13:11
@Marko, Next time I buy a car, I'm just buying a second set of calipers right off the bat... I go through enough of them that swapping in the alternative set every spring doesn't seem like a bad idea, and then I have an entire summer to take apart, clean, and rebuild the other set. I'll stretch that out to every other year if I think once a year is too frequent. I'm tired of having the damn things freeze up on me. It also amazes me how poorly automotive rotors wear.. I'm starting to think it's worth it to pay double for a thicker and better metal. You can't even machine the cheap ones and the warp so darned easily. Grr. Oh yeah, and on topic. I hate bicycle hydraulics! lol I still need to give a better set a try but most likely my next build will be cable actuated spyres. Also, I'll take the "toxic" Shimano mineral oil over the SRAM automotive fluid.
2018-09-05 09:49:19
@Ahlir Also, make sure the wheel is in the dropouts correctly... over looking that can lead to a lot of headache with self-adjusting disc brakes. I say this from experience... I had a set of SLX brakes that were a nightmare for a couple of months and it never dawned on me to really focus on how the axle was sitting in the dropouts. That finally solved a three month headache (for the most part). Venting isn't going to do anything except give a firmer response when you squeeze the lever... well, aside from pushing in the pistons. *edit* whoops, ok, you said that you were squeezing the lever all the way.. Yeah, refill away. I'm not even sure if bleeding is necessary. You should just top it off first and give a few squeezes, vent again... then do the bleed, compare, report back! I'd be curious if it's even necessary for the extra step!
2018-09-05 09:50:51
Thanks to this thread I replaced my back disc brake pads today. $10 and 15 min. I can totally see how it looks like the caliper is already all the way back when it isn't!
2018-09-17 12:27:28
And yesterday I got around to what thought would be bleeding the brake. (The brake lever had been acting as if there was no oil / lots of air in the system.) Oddly the system didn't want to take any oil (yes, I did it right). I gave up. When I everything back together, it worked. Just fine. So I'm not sure what happened. But at this point, I don't really care...
2018-09-17 20:00:58
you basically scared it into compliance.
2018-09-17 20:13:39