Cracked Shimano piston… Any hope of spares?

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  • Cracked Shimano piston… Any hope of spares?
  • Premier Icon joemmo
    Subscriber

    As title, I cracked a piston on a Shimano caliper when the bleed block slipped without me realising. ****ing oaf.

    Can you get replacement pistons anywhere? Google says no but maybe someone knows different?

    scotroutes
    Member

    There are some (non-Shimano) on ebay. I’ve not tried them

    bigyan
    Member

    Shimano dont sell spare caliper pistons, there are aftermarket metal ones on ebay, about £8 last time I looked.

    twowheels
    Member

    There are so many threads on this topic it’s depressing 🙁 I’m tempted to have a go at 3d printing some. The issue is heat insulation and I’m not expert enough to figure out what material would be best.

    The thing to bear in mind is those eBay ones are £8 each while you can often get a complete new XT caliper for £30 in sales (including pads and other spares that can be pillaged)

    If taking apart the caliper I’d also be wanting to replace seals (or at least have spares handy) and the other piston unless the brakes are < 2 years old. Thus suddenly you’re looking at >£16 + your time vs £30 – £6 (pads) = £24 for a new caliper with warranty.

    Premier Icon joemmo
    Subscriber

    Yeah thought as much. Bugger. The annoying thing is I got the pair second hand for less than it will cost to get one new one. I got the piston out by chipping it and the seal all looks fine but if the original parts aren’t available it’s a lost cause

    twowheels
    Member

    I would be interested if anyone has tried those pistons off eBay/AliExpress. The design looks quite simple to replicate (CNC alloy for the main part and then 3d printed insert using a material that doesn’t conduct heat).

    Premier Icon johnjn2000
    Subscriber

    I have an SLX caliper you can have if that helps? Nothing wrong with it just bought a new lever and caliper after a crash bent the lever.

    enigmas
    Member

    For the hassle and cost I’d just buy an SLX caliper for Approx £25 from germany, and that comes with a new set of pads.

    Premier Icon Akers
    Subscriber

    @johnjn2000 You can buy spare lever blades and lots of other small Shimano parts at sjscycles.co.uk, just not pistons unfortunately.

    Premier Icon Northwind
    Subscriber

    Like enigmas said, calipers are cheap and come with a set of new pads, I don’t like the whole disposable thing (my brakes are all ancient Formula Ones) but it works fine here

    Premier Icon joemmo
    Subscriber

    thanks for the offer @johnjn2000 but its a flat mount road caliper on my darkside bike that I need. Really annoyed with myself but will bite the bullet and get a new caliper… I suppose I’ll get a new set of pads and I have a spare piston at least.

    twowheels
    Member

    1) possibly stupid question- it is a ~22mm piston so has anyone tried a Hope 22mm phenolic jobbie (possibly machined down)? X2 is 22mm and quite cheap

    2) The minimum conceivable (to me) cost for a custom piston in solid high quality thermally insulating ceramic would be £6 in small runs.

    If using a ceramic insert into an alloy cup I think £4 is feasible.

    twowheels
    Member

    Mtbr thread where someone claims an X2 piston works despite the extra depth:

    https://forums.mtbr.com/shimano/shimano-replacement-pistons-994569.html

    I also found a discussion in French where someone mentioned machining around 1mm off.

    I might have a bash at some alloy + ceramic pistons too for fun.

    It’s possible those eBay ones are ok but they seem expensive for what they are.

    twowheels
    Member

    @scotroutes as I mentioned above that price is for 1 (at least that’s what it says in the listing)

    Premier Icon joemmo
    Subscriber

    interesting – I’m tempted to try one of the hope pistons but if it needs to have 1mm removed can the material be sanded? I don’t have access to a lathe

    Premier Icon njee20
    Subscriber

    I toyed with the replacements, but I just bought a new caliper.

    twowheels
    Member

    @joemmo- sounds a recipe for squeally brakes as I doubt you can keep the surface flat if sanding by hand. Maybe if you glue the sand paper to a flat piece of wood and bodge a jig it’s doable.

    I’m pretty sure you won’t need to remove a full 1mm.

    tomparkin
    Member

    I also had cause to ask this question previously — eventually sourced a second hand replacement caliper.

    I spent a while toying with the idea of rebuilding the broken one with an eBay piston, but in the end the risk of something going wrong with it didn’t seem worth the candle 😐

    Premier Icon joemmo
    Subscriber

    yes good point @tomparkin. I’ve ordered a replacement caliper, not too bad at £35 but was feeling a bit smug about picking up a pair of nearly new calipers for £31. No more smug 🙁

    damascus
    Member

    I can’t see why you would risk messing with brakes when a new caliper and pads are £35.

    Shimano unfortunately are throw away at those prices. If you want sustainably, replaceable etc then buy hope.

    I always put my old shimano brake parts on ebay as spares or repairs. Someone always buys them as you can’t get new parts.

    I found myself in the exact same position before.
    I went ahead and ordered the Hope X2 piston HBSP235.

    https://www.sjscycles.co.uk/brakes/hope-x2race-caliper-phenolic-pistons-22mm-hbsp235/

    It is fractionally taller but identical diameter to the SLX M675 piston it replaced and there was enough space between the pistons to fit new pads without rubbing. You just wont be able to get two Hope X2 replacement pistons in, one on each side without sanding some pad material off maybe.

    Just obviously don’t try and use the Hope piston seals!!! Because Hope are dot fluid they use a different rubber for their seals and it will expand like crazy in the mineral oil shimano brakes use.

    Sizes for the seals are identical though but no industrial supplier anywhere that I came across sold the correct size square seal made in NBR rubber that you need for shimano back when I was searching.

    Premier Icon nixie
    Subscriber

    I have at least two leaking calipers if anyone wants pistons. One was allegedly brand new.

    On a road bike I’d be tempted to replace the caliper with a hope road one (that has the proper seals).

    Premier Icon joemmo
    Subscriber

    yes I’d love to fit some RX4s but I’m already over budget after the piston incident so they’ll have to wait.

    Premier Icon joemmo
    Subscriber

    Just as an aside, I was able to pop out the good piston (literally) by using the tubeless compressor on my pump and blowing air into the caliper so at least I have a good spare.

    Tempted to try and get a cheapo caliper to cannibalise on eBay and see if I can rebuild it though…

    Premier Icon nixie
    Subscriber

    Are they 22mm?

    Premier Icon joemmo
    Subscriber

    I haven’t measured it but yes, the spec sheet says ‘oversized 22mm ceramic pistons’

    Premier Icon johnjn2000
    Subscriber

    Bloody good job you didn’t take me up on my offer. The boy was changing his rotors yesterday and was having trouble aligning the calliper, turns out the piston was screwed so I had to swap my spare to his bike. He has a race on Sat so that was a stroke of luck.

    Hope you get it sorted

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