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Hello everyone!

I'm in the UK and I have a Cub Cadet CC114HA mower which has stopped moving....

I have stripped the back of it off to have a look across the drive system.

I have checked the fluid in the Hydro transmission which seems to have the adequate fluid level, I have also checked the idler pulleys and they are moving freely, the belt is worn and I will get a replacement but doesn't look worn enough to cause significant issue. Before it stopped moving altogether it was gradually getting slower whilst cutting until it needed to be pushed to get going at a crawl. There was a chattering sound throughout this time but I can't seem to pinpoint this, the idler pulley on the brake system seems to move as does all the return springs leading to the hydro unit. I have checked the bypass valve on the back and that seems to engage and disengage correctly. When lifting the back up and spinning the wheels 1 turns forwards and 1 backwards which I am presuming is correct for the transmission. My only concern and I am likely wrong is that when the back wheels are in the air and I spin the transmission pulley, no matter what is engaged or disengaged the wheels do not move.. Could this point to a transmission issue?
I am spinning pulley 28 in the above diagram which I believe should turn the wheels but I get nothing.

I would greatly appreciate any help as my grass is starting to resemble a field! If anyone knows the drive belt size also that would be great!

Thanks