Bunny, maybe you need to try bleeding the brakes before doing anything else. If you’ve replaced the rear brake cylinder there may be air in that line. This happened to me and my brake pedal just didn’t feel quite right. I used my compressed air driven one man vacuum bleed kit to bleed the system, but it obviously didn’t shift all the air. The two man method is the most reliable way to bleed brakes in my experience, and one Saturday afternoon I persuaded Julia to pump away at the brake pedal while I fiddled with the bleed valves. This cured the problem and all I then suffered was Julia complaining about her aching leg for an hour or so 😂