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?

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

https://www.ebay.co.uk/itm/Metal-Piston-Hydraulic-Bike-Brake-Caliper-Replacement-For-Shimano-M785-M8000-675/183811528396?

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

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.

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

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).

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.

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.

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

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

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.

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.

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.

£8/pair, delivered

https://www.ebay.co.uk/itm/METAL-PISTON-HYDRAULIC-BRAKE-CALIPER-PART-FOR-SHIMANO-XT-M785-M8000-SLX675-STRIC/132955100561?

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

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

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

@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.

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 😐

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 🙁

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.

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).

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

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…

Are they 22mm?

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

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