One piston is not coming back as easily as the other one

Hello
I'm building the front brake.
I fitted new seals and new pistons.
One piston can be put off really easily but for the other one I need to apply air pressus, is that normal?
It's really hard to push on the other piston.


Is it normal?

Thank you

 

Did you apply a little red grease or brake fluid when assembling?

 

How hard was it to put the piston in originally?

One one caliper that I rebuilt in the past caught the edge of the square section seal and rolled it over as I pushed the piston in.
The piston was really stiff going in and was very stiff to move like you are describing.

I removed the piston again and found the seal rolled.

It was a long time ago and I can't remember for sure if it was the dust seal or the actual piston seal that rolled over.
I think it was the dust seal.

 

Thank you for your help.
Yes I put the red grease. Honestly it's really hard to move it. I thought it was because of the suction because this one is at the back.
Should I be able to push them really easily or even retired them by hand?
It looks like the seal is too small when I try to pull it and can see a little bump on the seal, is this a sign of a wrong seal?

 

It sounds like you rolled/pinched it on assembly.

 

I have found that spinning the pistons, while pushing them past the seals, normally takes care of any chance of rolling the seal.

 

This.

 

Alright thank you for the tips!