Author Topic: Worth trying to rebuild Shimano hydro calipers?  (Read 684 times)

Worth trying to rebuild Shimano hydro calipers?
« on: 08 May, 2022, 08:22:08 pm »
I have Shimano RS505 brakes/shifters on my road bike (with 105 shifting kit, because that was the only way to get 105 and hydro brakes in 2016). I've not ridden it much for a couple of years, but finally got myself healed enough to start riding more this year. The front brake was alarmingly noisy this morning, and I had some pads (I'd not done any maintenance on them in ages, so it was on the list), so I figured I'd just pop in the new pads and see if that fixed everything.
When I took the pads out, I couldn't get one of the pistons to move back in.  Every time I pushed it (really hard) there was a sort of grinding noise, but no movement. Eventually, I figured I could push it out a bit further and clean it, but it made no difference. So I pushed it it a bit too far and leaked oil out of the seal over the floor (ooops). Still it grinds and won't go back in.
I could just hand it to a bike shop, but I don't want to be without the bike as it doubles as my turbo bike - am I daft for thinking I can take the calliper apart and rebuild it? I've done a course on hydro brakes, but that was ages ago.

Has anyone done this successfully? I think I'll give it a go - if I screw it up then I can always just buy a new calliper (or take it to a bik shop for them to go down the new calliper route).

Re: Worth trying to rebuild Shimano hydro calipers?
« Reply #1 on: 22 May, 2022, 12:05:11 pm »
Well, I took apart (eventually). I tried to use the bleed kit to push the pistons out (using water - would need a really good flush out after anyway), but that didn't work 100%, so I just dismantled the calliper and pulled the pistons out. The first piston broke as I pulled it, and I was really beating myself up over breaking it, so I was really gentle pulling the other one out. I managed to get that one without breaking the piston, only to discover that the reason why I was unable to push it back in (what started this saga) was that the back of piston was all broken up inside the bore of the calliper!  :o That explains the graunching noise when I tried to push it back, and why it simply wouldn't go back no matter how much pressure I applied.

2022-05-22_12-07-10 by duncancmartin, on Flickr

I've had a bit of a hunt for replacement pistons on eBay, and the only ones I can see are for MTB callipers, so I guess road ones just aren't available. :( Does anyone know if the MTB ones and the road ones are interchangeable? And is it worth replacing the pistons, or is the caliper destined to be annoying and leaky from now on anyway? I can't see any damage on the bores, just a little at the back of the cylinder.

Secondhand callipers are pretty cheap, but who knows how long they will last or if they are any good.  A new Ultegra calliper seems to be about 70 quid - does anyone know if that would be compatible with my BR505 (non-series 105 replacement) levers?

Re: Worth trying to rebuild Shimano hydro calipers?
« Reply #2 on: 22 May, 2022, 02:15:20 pm »
AFAIK the pistons and calipers are all interchangeable. I put one of these in a 105 caliper - the reason it was missing it is because I broke one in a Dura Ace one and needed a replacement sharpish so ordered a cheap(er) 105 and stole a piston temporarily!

Since you've split the piston you might want to spend the few quid more and replace all the seals as well, so this listing would be better:

Re: Worth trying to rebuild Shimano hydro calipers?
« Reply #3 on: 22 May, 2022, 04:38:15 pm »
If they will fit, then I'll give those metal ones a go - I'll need to replace both of the pistons.
And I realise they say they will fit most other shimano road callipers, so I guess it makes sense that they will fit mine.
Thanks 🙂


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Re: Worth trying to rebuild Shimano hydro calipers?
« Reply #4 on: 23 May, 2022, 10:29:01 pm »
Shimano don't make replacement pistons.  Anything you see on ebay are what some random Chinese factory has made, so you're taking a gamble about how well made they are.
“Life is like riding a bicycle. To keep your balance you must keep moving.” -Albert Einstein

Re: Worth trying to rebuild Shimano hydro calipers?
« Reply #5 on: 28 May, 2022, 09:48:10 am »
I ordered the replacement pistons - they were cheap enough for it to be worth an experiment. And then I was the only bidder on a secondhand calliper, which arrived yesterday looking very clean and shiny! So I'll put the calliper on this weekend and see what the pistons are like when they arrive - who knows how long either will last (or how well they will work), but at least I have a spare now. And I learned how the brake callipers work, which is kinda satisfying. :)
I'll report back when the pistons arrive and I actually get around to using them...