Brake problem after changing front brake pads

[Tom6]

Hi, this is my first time on here so please be patient with me. I've got a 2003 celica 140 and about 3 weeks ago I changed my front brake pads which I've done on all my cars. After changing them I pumped my brake peddle and the peddle felt normal for a second but then the peddle would slowly go down to the floor. With the engine off the brakes feel fine, I rechecked the pads but they looked fine so I bled the brakes but still no joy. I took it to my mechanic and he also bled the brakes and checked everything but couldn't find a problem so he said I must have flipped the seals in the master cylinder when I pushed the pistons back and I would need another one. I found a tested secondhand one and had it fitted and had the brakes bled again but it's still exactly the same. When the peddle goes to the floor the brakes work ok but I don't think it would pass an mot. My mechanic can't find the problem and I've tried everything I've found on the Internet with no luck. Would be extremely grateful for any help you can offer, thank you.

 

[Tom6]

Just an update to stay still haven't found the problem, going to try and take it to a different mechanic and see what they say. If I still haven't found the problem by the time my mot comes round don't know what I'm goto do 😞