Saga of the brakes continues.....now sticking on won't return

My brakes failed on me last week on the way into work. On inspection the cylinder was knackered on the rear OS wheel.

Got a new cylinder and fitted this morning. Bled the brakes at the wheels as per the book says, but now the cylinder that I've replaced stays on and won't return unless I open the bleed screw on the back and manually force it shut.

Any ideas what could be causing this? Am I missing something simple?

Bus is a 72 crossover drums on rear and disks up front.

Thanks in advance.

Gus.

 

Could be the flexi hose on that corner is collapsing and holding the fluid pressure.

 

Cheers, will check it out now and see if there's anything a miss with it.

 

that might explain why the old one failed, If it suck on, the brake would over heat and knacker the seal !!