Leaking calliper on Shimano road disc brakes?

Rear brake on my road bike has been pretty ineffective for a little while. I figured maybe it needed a bleed and gave it new pads at the same time (and cleaned the disc).

But it didn’t seem to make much difference – still crap and noisy. K just cleaned the salt and winter crap off the bike and pointed out how greasy it was all around the back end. Bleed screw was tight so looks like maybe it’s been leaking.

I’ve never had a caliper *leak* on any disc brake but I can’t see what else it could be (hose is tight) – is this a known/common problem?

I think it’s one of these – it has the hidden bleed nipple behind a little plug and a separate hex that you open to bleed. Current designs don’t seem to be quite the same.

Googling brings this up. Sounds like a cracked piston https://www.bikeradar.com/news/shimano-r785-road-hydraulic-disc-caliper-failure/

Repair or replace? are all callipers compatible?

Yep, had exactly the same issue on those Callipers fitted to my 2017 Arkose.

I went though about 3 sets of pads, changes the discs and actually stripped the rear calliper down to change the O-rings before giving in and replacing them with a set of Hope road callipers – which completely transformed the braking performance – they are also absolutely silent unless you are riding in heavy rain.

As for as i’m concerned those callipers are not fit for purpose.

I just went and cleaned it all up, stuck it in the stand and wrapped paper around a bleed block and couldn’t get it to leak (and there’s no real loss of pressure – it’s not like the lever’s pulling to the bars).

Odd.

Still looks like a current model as well – https://bike.shimano.com/en-EU/product/component/ultegra-6870-di2/BR-RS785.html

although it looks different to the model that people are selling as the same model number

I just went and cleaned it all up, stuck it in the stand and wrapped paper around a bleed block and couldn’t get it to leak (and there’s no real loss of pressure – it’s not like the lever’s pulling to the bars).

So, I’ve stripped several Shimano MTB calipers that were definitely leaking. Funny thing was I was pretty sure that they weren’t leaking under pressure. I did exactly what you did; blue roll round the bleed block & left them pressurised overnight. There was no sign of fluid getting past the seals or loss of pressure. The cause of the leaks in the calipers I had was a build up of corrosion in the ring groove under the seal which was allowing fluid past. Once this was cleaned up the leaks stopped. Another observation was that the calipers themselves are pretty flexy when under normal braking loads & you can’t really see this unless the caliper is off the bike. Good when they work otherwise difficult to troubleshoot.

The cause of the leaks in the calipers I had was a build up of corrosion in the ring groove under the seal which was allowing fluid past

How easy is this to do? remove caliper from bike. leak mineral oil everywhere. then what – I’d not know how to get the piston out? then did you use the same seal or buy replacement?

(I’ve found an old thread on here now – https://singletrackworld.com/forum/topic/leaking-shimano-calipers-possible-solution/page/2/

Now my pads had been wearing unevenly which is also picked up as a potential cause of issues. I reckon I need my mounts faced…

You’ll need to remove the caliper from the bike and the hose then split it (if it is a 2 piece). Then ideally use compressed air to pop the piston, having wrapped it in a rag to stop it firing out too far. The use a pick to gently remove the seal. Clean and re-fit, then reassemble and bleed.

It isn’t difficult, but would take a bit of time. You could maybe pop the piston using a pump if you had a suitable way of attaching it. A bleed kit might have appropriate joints that you could bodge a pump to.

How easy is this to do? remove caliper from bike. leak mineral oil everywhere. then what – I’d not know how to get the piston out? then did you use the same seal or buy replacement?

The two piece calipers are easy to strip. The two halves just unbolt exposing the mating surface & pistons. I used compressed air to dislodge the pistons. The seals were fine & not part of the issue. Once the seals were out the grot & corrosion in the bottom of the groove was obvious. I like trying to fix things rather than ditch what was a fairly new set of brakes. I’ll find out how long this fix works as I’ve just put them back on a bike.

idea of slapping an XT caliper on there out the window due to different fitting.

Seroiusly considering some RX4s….