Hydro movement problem

I have a '10 72" turf tiger that was getting a noisy right side hydro (spongy) and sporadically letting the mower move.(more when cold). It would operate while on the jack though. I was thinking the wheel motor was bad and flushed the system and changed the motor with a spare rebuilt one that I had on the shelf as the original was leaking pretty good too.But it hardly wants to work or make any noise now.



I'm thinking the pump must be bad.
Or would air be in the system, even after running...

Hydro movement problem