Magura mt7 piston throwing oil from inside

[jene]

When I was cleaning the pistons before bleeding the brakes I made this but when I was trying to lubricate one of the sides of one piston I took it out too much while I was pulling the rear lever, then I noticed that it was oil coming from inside the piston... Then I cleaned it and bleeded the brake two times (there were a lot of bubbles) but the lever is too loose and it does not brake. I see that it's oil still in the piston... So not sure if I damaged it... Any idea of how to fix it?

 

[Stihldog]

After the initial install and full bleed of MT7’s brakes, a mini-bleed(master cylinder) may occasionally be necessary. A mini-bleed process is a good opportunity to clean the calliper and pistons. These are some of the tools that I use for a mini-bleed and/or piston cleaning.

I’ve never had a piston pop-out or start leaking fluid so I don’t know the process of re-inserting a cylinder.
The small black tool (r3pro) is what I use to prevent a piston from over-extracting and thus leak brake fluid. It allows each individual piston to extend for cleaning. I would worry about contaminating the brake pads or rotor. I clean this area with ISO alcohol or brake cleaner.
I’ve only cleaned several (less than 20) pistons and callipers for MT7’s but never had an issue with Royal Blood leaking into the pad area.

R3pro has a number of 3D printed products for Magura brakes.
Someone here may know how to re-insert a piston.

 

[jene]

Thanks. Bleeding process was apparently right but it's something wrong after popping up the piston. Lever is totally loosen. Lack of pressure. No idea how to fix it.

 

[RustyIron]

You need to bleed the brakes properly.
There can be no air in the system.
Start over from the beginning, and do it again.

 

[RebornRider]

R3pro has a number of 3D printed products for Magura brakes.

Thanks for that! I've been using a screwdriver with a wide blade and a very small c-clamp to extend one piston at a time. I thought about making my own part that would block 3 of the 4 pistons, but I'm happy to pay for something clever that already exists.

Edit to say that, so far, I've not had to learn how to re-insert a piston, but I can imagine there would be a leak if it was not done perfectly. But the spongy lever suggests air in the system as others have already said.

 

[RustyIron]

I've not had to learn how to re-insert a piston, but I can imagine there would be a leak if it was not done perfectly.

It's a circular piston that fits in a circular hole that's sealed with a circular o-ring--
no different than putting the round peg in the round hole.
It's the sort of thing that would be almost impossible to get wrong.

 

[Shjay]

I don’t know if link will work but this is a good technique for a good bleed to finish off

 

[RebornRider]

It's a circular piston that fits in a circular hole that's sealed with a circular o-ring--
no different than putting the round peg in the round hole.
It's the sort of thing that would be almost impossible to get wrong.

Really? Circular o-rings? I thought they were square cross-section. Get a twist, get a leak.

 

[RustyIron]

I've not had to learn how to re-insert a piston,

Really? Circular o-rings? I thought they were square cross-section. Get a twist, get a leak.

Yes, they are circular, the cross section is square, and the leading edge of the piston is rounded.
The clearance between the piston and its bore is so small that I would imagine it to be virtually impossible to get it wrong. Frankly, if I wanted to screw it up, I don't know how I would go about it. So if you ever remove your pistons from the caliper, whether intentional or accidentally, just make sure the piston is clean and then push it back in.

Hint: If you push the piston out and reinstall it, there will be a lot of air in your caliper. You'll need to bleed the brakes, but start by pushing oil through the lever end. If you start by pushing oil up through the caliper, you're pushing all that air through the hose and the lever assembly. There is more opportunity for minute bubbles to get trapped. When you start from the top, you're getting rid of the air with minimal potential for little bubbles to get hung up.