Afternoon everyone,

just talked to the LBS on the phone.

Good news:
He had the pads and wheels removed while doing the bleeding.
He also used the yellow bleeding block while doing it.
When he tested the brakes, no pads and rotors where installed.
So pads and rotors are not contaminated.

Bad news:
He tried the bleeding again which works.
But everytime he pushes the brake levers, oil comes out down at the pistons.

He doesn't understand what he did wrong nor what's happening.

Question to you:
Is this fixable and if yes:
should I (given that brakes are a concern of safety) and how?

Might be able to upload some pictures/videos later!

The ceramic pistons in the newer calipers are notorious for getting easily damaged.

Could be the case here

I'll second this. This sounds very similar to my experience having 2 Shimano pistons crack on me recently while doing service. Both times it was due to me being dumb and rushing the process, so I didn't pay attention to making sure the piston were pressed in completely straight (Pro-tip, use thin flat bar that can pass through the caliper to press them in, like a cone wrench, so you can more evenly apply pressure). Several millimeters cracked off the back surface of the pistons and a shard of the crack propagated past the seal so oil would flow out when the lever was pulled. I was able to disassemble the 2 halves of the caliper body to get out the broken pistons and replace with extras I had from the bin. Unfortunately Shimano does not offer the pistons or seals as rebuild parts, so you might be looking at new calipers.

hey hey,

brought the bike to another LBS (usually taking care of my Quintana Roo PR6).
He'll have a look at it. Gave him your hint on the broken ceramic pistons.

The absolute nightmare at the moment is the availability of spare parts.
If I actually need two new calipers, the bike is out of order for how long? End of 2021?

As others say pistons can be cracked.

Over time they can wear too.
On past mountain bikes I've had a couple of shimano calipers start to slowly weep fluid past cylinders and contaminat the pads. Usually got about 3 years or so from memory before that would happen.
One really annoying thing is Shimano don't do service kits. So it was new caliper time.

(I have lovely Hope brakes now and all spares available. Quality engineering from Lancashire 😎).

The other alternative is for some brakes there are aftermarket pistons available.

Here's an example for a mountain bike brake

https://www.amazon.co.uk/...B07ZP6Z7DD&psc=1

Would just need a bit of searching around for the right size for the road brake cylinders.

It is highly likely that your mechanic has no idea what he is doing and broke the pistons.

I would suggest never going back to them.

Buy two new brake calipers and install them yourself.

hey, trisomemari, did the other LBS figure it out?

It‘s been true collaboration between both.
Was broken pistons. The other LBS had two spare calipers, sold them to the first LBS who attached it to my bike.

Paid the hours for bleeding 2 brakes and some mineral oil.

Good result in the end 👍

Jupp!

Still registered that there is some air in the hose of the rear brake.

Ordered all the stuff to do the bleeding myself.
Will try the version with the cup on the lever first, not a full bleed.

Hope this won‘t end with part 2 of that thread 😜

That was the only logical explanation....but two of them, at the same time?

The bike shop had no idea how to work on brakes.