John Deere LT166 with K51 Won't Move

[mac5551212]

I just picked up a LT166 for free and the motor runs great and it is in good shape but it won't move. I just pulled apart the transmission and all of the gears were in great shape and the pistons and cylinder walls looked to be smooth and in good condition. The drive belt is rotating the shaft in the transmission when I remove the brake but I am getting no movement out of the axle shafts. When I refilled the K51 trans I could only get about 1.5 quarts into it and it asked for around 2.3 quarts. Could it be that it is just low on fluid and or needs to have air bled from the system?

 

[mac5551212]

Managed to get the other quart into the transmission. Needed to remove the large plug, pull out the spring, and then pull out the flat fliter. The oil can't pass through the filter unless it's under pressure. Tractor is good as new. It even pulls wheelies!