WD45 Rear Wheels Locking Up

A couple of weeks ago, just as I was finishing disking, and heading back to the shed my WD45 locked up and wouldn't move. It was like I had applied the brakes, both rear tires locked up. I pushed in the clutch and let it out and continued to drive. Again it locked up the rear wheels so I put it in neutral and pulled it back to the shed. Now that I have finished planting it's time to look into the problem. Any suggestions as where to start and what to look for? I am pretty sure it's not the brakes and the transmission shifts into all gears and reverse so I'm thinking it's in the differential and/or final drives. Clutch seems to work fine also. Thanks in advance.

Do you have oil in the rear end. The only time I've seen them lock up (three times, a WD and a D17 and a D15) is because the rear end was dry. An old mechanic once told me sometimes farmers would neglect the oil and have them lock up and he would just put oil back in, rock them loose and away they would go.

Checking the trans/differential oil was first on my list. I have checked the level in the past, usually each year, and have had to add some. I will let you know what I find. Thanks for the advice.

All I can add is that the final drives are not the issue. It's the rear end or the transmission.

The rear plug  behind the clutch pedal is for the transmission AND differential. The front plug underneath the battery box is for the hand clutch and PTO gears. What most people don't understand is BOTH compartments share the same oil and it runs back and forth between them. About 4 gallons total between front and rear check plugs. When you fill one up to the top, it eventually levels out between the other one and then neither are really full. The bad part is, he said he has added oil in the past. There has to be a leak somewhere.

you had stated you put in neutral and drug it back to the barn.  were the tires free when you pulled it?  If it were the rear locked up or the brakes wouldn't the tires still be locked up even if the tractor was put in neutral?

Well this mystery has been resolved. I went to drain the trans/differential to find zero oil from either plug. My son who helps around the farm and does a lot of the maintenance had drained and flushed the trans/differential and left me a note saying he had done so and would go pick up the gear oil to refill. The only problem was I didn't see the note which fell off the WD45 and on the shop floor and he had went to work and was going to finish the job the next day. Luckily no damage was done and the trans/differential is now full. It takes 17 quarts to fill both compartments. Live and learn. I told my son next time he decides to help to take the keys to the WD45 with him!!!!