Here is the manual for the 2000, 3000, 4000 and 5000,
https://data2.manualslib.com/pdf5/106/10527/1052659-ford/2000.pdf?6cbe67364f75a5d5bf88cf05a43220e6Here is a video of 1 with the bucket attachment showing the filter location on it,
https://youtu.be/GmBbi4CUK7o
And here is a answer;
http://www.fixya.com/support/t26353627-hydraulic_filter_1964_ford_4000_tractor
More info added;
The rear differential fluid level check plug is behind your right heel as you are seated on your tractor. Once again, it is a small square-headed pipe plug. You may have to squat down to see this plug.
The rear differential reservoir is where your hydraulic pump draws fluid. The filler cap is on top of the rear differential center housing. (some have two filler caps there - both serve the same purpose).
The drain plugs are square-head plugs that are recessed. You have to get under the trans and rear end to see them. Also, the drawbar may obscure the rear end drain plug. I have to unbolt my drawbar and slide it back to get to my rear drain plug.
Use FORD 134A tractor hydraulic fluid or equivalent Universal Tractor Fluid in both reservoirs. You can get UTF from Tractor Supply Stores, auto parts stores, Wal-Mart, etc.
There is a hydraulic filter and suction screen deep down below your hydraulic lift cover (under the seat). If you want to change the filter, and clean the screen, you will have to pull the hydraulic lift cover. And there are other items to remove before you can access the filter. I feel that you will need a shop manual before you tackle this job.
If the hydraulic pump will not pump, after you've determined that the hydraulic reservoir is full, you can prime the hydraulic pump by pulling the test plug on the pump and rigging up a clear plastic line back to the fill port. Start the engine and let it pump until all the air bubbles are expelled.
After you get your lift working, refill the rear reservoir with the lift arms raised.
