I have a 2008 John Deer X300 riding mower. I parked it and when I went to use it the next day would not move forward or backwards. It is hydrostatic. What could it be? How do I check fluid for hydrostatic?

Quester edited for clarity and spelling 'deer' to 'Deere'.
Question moved to John Deere D110.

Try the 5 minute fix, but your sounds like the hydrostatic transmission.

https://www.google.com/search?q=John+Deere+D110+mower+stops+after+5+feet

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John Deere mowers, for the most part, use hydrostatic transmissions. These use an oil of some type (they vary by model) in the transaxle to provide hydraulic pressure to move the tractor. Older tractors will eventually experience some oil leakage over time due to seal wear. If the level gets too low, then you fail to move. Check the oil level in the transaxle. The location of the reservoir varies from model to model. If it is low, after determining the correct oil to use, fill to proper level. Then, start the tractor and work the hydrostatic drive lever forward and backward slowly and continuously until you get full speed operations in both forward and reverse. This can take a few minutes until all the air has been purged from the system.

the hydrostatic pump is out on your pedal forward and reverse

Go to john deer dealer they should be able to print u of that diagram for you.

Likely the belt is mispositioned or somehow in a bind.

check the connecting rod to the tranny. follow the gear handle and you should find a rod connecting the handle to the axle make sure you're in neutral and adjust the rod until the handle starts to move

if there is no problem with the drive belt getting power to the transmission, then the transmission is failing.

The electric clutch is to power the blades/mower deck. There is a belt that drives the hydrostatic pumps to power the wheels. Make sure the Parking brake is OFF. Could be a belt, spring, idler pulley.

I’m happy to assist further over the phone at https://www.6ya.com/expert/rolandw_c013176d62ee17ae

This look like it would be hard but it only takes a few minutes to remove. First put it on jack stands and lock the clutch down to release the belt so you can slip it off the pully. Then there are only about 6 bolts and two control shafts pins and its is out. It make things simpler by removing the deck first.