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I was bleeding the rear brake on my commuter last night, Shimano R785 Di2 hydraulics. Bled from the caliper end with a syringe and instead of fluid appearing in the little pot screwed into the lever end, it all poured out onto the floor 🙁 It would appear as though the diaphragm has died and the fluid is coming out of the little breather hole.
Apparently Shimano don't sell spares which effectively means my previously top-of-the-range lever is now junk.
Anyone experienced the same, or have any solutions? Can any other manufacturers parts be swapped in (doubtful I'm sure) but I'd rather not chuck away a complete lever for a £1 seal....
Bump
Why not send the brake back to Madison? You've nowt to lose.
Has the diaphragm split or just come out of its housing? I want to check that first. You might be lucky and can just pop it back in place.
It's probably worth trying to find a service guide though first to see if there is anything obviously wrong with bleeding process, although what you described sounds ok.
And as much as I really want hydraulic brakes on my road bike, this is why I've held off. On an mtb you just replace the brake lever. Bit different when it's part of the shifter.
I know it doesn't happen often, but I like to run my kit for a long time and look after it.
Maybe we're about to see the far end of the bath tub curve.
@woodlikesbikes as the cover for the diaphragm has never been removed, I'd be surprised if it has come out of the housing, but it wouldn't hurt to do a bit more diagnosis before ditching.
I had initially thought that I'd killed it through reverse bleeding without checking prior that this was OK with the Shimano brakes, but subsequently I've read that this is exactly the way Shimano recommend for a full bleed. Unfortunately service guides are not available, as Shimano don't supply any of the parts, except the little silver plastic front cap. Not much point in showing people how to strip down a unit and show them all the internal parts which they can't buy 🙁
Onzadog
Member
And as much as I really want hydraulic brakes on my road bike, this is why I’ve held off. On an mtb you just replace the brake lever. Bit different when it’s part of the shifter.
I've got the same levers as above and they're now over 5 years old and have been used for commuting over 20000km. They're still fine.
Unless you're gonna give one to the OP, that's not massively helpful.
😉
No idea if its the same with the road levers, but the internals of the MTB levers are all the same and I happily transplanted master piston and seals from new Deore levers into XTR ones. Might be worth an investigate.
(must admit I've been dreading my RS785 levers going the same way - I had the calipers changed under warranty, but that's now gone)
@JonEdwards had it been a master cylinder seal, yes, I reckon it would be worth a shot. However I'm not sure the diaphragm would also be swappable as it seems pretty much designed to fit the space on top of the hood. I'll certainly do a bit more investigating before replacing. Actually as I'm running Alfine, I don't need the Di2 buttons on the left hand side, so any hydraulic drop lever would do the job, but it would be nice for them to match...
Must admit I've had problems with my shimano road hydros (RS685 and ultegra calipers). 3 leaking calipers in under 2 years.
Changed to Hope calipers and now the rear caliper has cracked at the pad screw.
In 10 years of MTB hydraulic and road cable calipers I've had one failure due to me cross threading something.
I suspect the dowsing with salt and road crud is wrecking these things something chronic.
Another quick failure and I'm jacking it in and going back to rim brakes.
turboferret
Subscriber
@daffy fancy a swap? 🙂
Not really, but ST-R785s usually do go fairly cheap on ebay.
https://www.wiggle.co.uk/shimano-r785-disc-brake/
Could get a new one? Prices seem crazy good at the moment.
My rear caliper seized from lack of maintenance a while back, so I replaced it. Surely you can just get a new caliper?
https://www.sjscycles.co.uk/brakes/shimano-brrs785-road-post-mount-hydraulic-disc-brake-caliper-front-or-rear/
or a cheaper model (mtb brake calipers also are compatible) or look on EBay, I've seen cheaper ones on there.
@webbierwrex that is an excellent price, I think I'll do that, thanks 🙂
@DezB it's the lever instead of the caliper unfortunately, lots of options had it been just the caliper
Oh right! Never known one do that before. That's a bugger.
The Wiggle ones are all European type of hoses, right for rear, left for front, but as I'll keep the current hose which is an awkward internal routing, it's of no consequence
You could try contacting https://www.sjscycles.co.uk/ they carry a lot of Shimano spares.
I’ve seen master cylinder and seal kits for Shimano mtb levers on AliExpress, might be worth a search for road lever spares.
So, I had another look at my brakes last night. I took off the top cap expecting the diaphragm to resemble something out of an old Hope lever, but it was somewhat different
In my left hand is the cover upside down, with the rubber diaphragm visible centrally. There are a few breather holes located below the diaphragm in the un-anodised area. It seemed to be intact and correctly located, but a 2nd attempt at reverse bleeding still resulted in fluid escaping from around the cover, regardless of how tightly it was screwed down.
Given how simple the rubber was, I decided to improvise and made a slightly larger one from a bit of inner tube (original sat on the bench adjacent). Again, some leakage while bleeding, but I managed to get a relatively firm lever, so we shall see if it's at all functional tomorrow....
Excellent bodging!
So apart from squealing like a pig, as they always do in the wet, I am pleased to report that I now have a working back brake again.
If I'm honest I've never been particularly impressed with the stopping power of the 785s so it's nice to have a pair to work together as just the front was distinctly lacking.
Bodging a brake is brave.
Can you order that specific part? Or salvage one from a broken set?
Or are you confident that it's just a bit of rubber?
@damascus the issue is that Shimano do not sell spares for brake internals. I must admit that I haven't fully diagnosed the issue - the original diaphragm looked completely intact and it still leaks slightly when reverse bleeding even with the new bodge, but it does work, so I'm relatively happy for the moment. I've certainly bodged worse before 😀
I'd swap that part with the one from the other lever and see what the problem is. If it's just the cover is somehow warped/damaged then you'd likely be able to salvage one from a crashed lever.
@scotroutes what I don't understand is how it's failed - it worked fine before I took it off the bike for a frame repair. Until the other night, the top cap had never been off and hadn't leaked....very strange
Yeah, that would have me puzzled too, hence my suggestion.
I hesitate to suggest user error as you clearly know what you are doing but I can imagine it being damaged/leaking if the bleed syringe was being pressed really, really hard and the funnel wasn't attached or somehow blocked.
To be clear - I'm not accusing you of making this mistake, just hypothesising
@scotroutes I'm not ruling out the possibility that I may have damaged it during the reverse bleeding - I didn't research whether this was a viable method for these before doing, and firstly assumed that I'd buggered it up myself. However, after discovering that this is in fact the published method, I was somewhat relieved, but also rather perplexed... Had the funnel screw been still inserted, then excess pressure would have no other escape route than through the diaphragm, but this wasn't the case. If there were a seal kit readily available I'd do a rebuild as a matter of course to be on the safe side, but I'd rather not spend £80 unnecessarily
Do you think you could have over filled it and it's leaked out of the overflow?
My mtb xt brakes do this, I'm guessing the road ones are similar in design.
Or maybe the seal on the screw in reservoir wasn't in correctly so it leaked out?
Its just strange that it's all now working fine.
Perhaps there's no issue at all?
Its just strange that it’s all now working fine.
Well apart from...
the original diaphragm looked completely intact and it still leaks slightly when reverse bleeding even with the new bodge
@damascus if it were overfilled it would have just come up into the reservoir, I don't see any way of overfilling assuming the drain/filling screw has been removed.
The leak wasn't from the reservoir, it was from the diaphragm cover plate and dribbled all down through my bar tape 🙁
@simondbarnes yes, it's strange, never encountered this level of weirdness. I'm not a total noob when it comes to hydraulics. Been playing with them for over 20 years now, including lots of fun trying to get the ill-fated Cullimore/Middleburn ones working properly!