Final drive on track excavator

Took apart the hydraulic side of the final drive on my mini excavator to examine a cracking noise. The noise was likely coming from the main bearing side. Anyhow, everything went back as it came apart but the drive does not turn now - it did beforehand. Is there a priming mechanism , presumably they dont air lock? Anyone know any likely reasons why it won't turn on reassembly?

Final drive on track excavator