Ford 8n tractor.when i put a load on the pto , it pops off

It is frozen, hit it with a soft faced hammer.

Ford Tractor Hydraulic System - My Ford Tractors

www.myfordtractors.com/hydraulics.shtml

All N-Series Tractors - Ford-Ferguson 9N, 2N, and Ford 8N ... 6 - How long has it been since you changed the hydraulic fluid? ... If that didn't do it, read on. ... then remove the bottom bolt from the inspection plate that has the hydraulic dip-stick.

Yesterday's Tractors - Fifty Tips for Ford 9N, 2N and 8N ...

www.yesterdaystractors.com/articles/artint268.htm

I'd like to say that the reason I have an 8N Ford tractor is because that's the tractor ... The N tractors have a common sump for the rear end, hydraulic pump andtransmission. ... (Read the label.) .... Take the inspection plate with the dipstick off.

Ford 8N, 9N, 2N, NAA Tractors Information - SSB Tractor ...

www.ssbtractor.com/wwwboard/messages15/

Helpful information and resources on Ford 8N, 9N, 2N, NAA tractors from SSB Tractor, a leading provider of tractor parts, manuals, implements ... 1944 ford 2n: What type of oil to use? and whats the oil pressure should be? ...... N Series Trans/Hydro Fluid - Interesting To Read ... Ford NAA/Jubilee Hydraulic dipstick location?

Sometime around 1950 Ford tractors started using "live PTO". Prior to that the power lift for equipment required that the PTO be on and running (turned on by a lever on left side of chassis below the driver's seat). So 'yes' the older tractors (many in use today) require the PTO to be running in order for the lift arms to lift equipment. I find this very annoying when trying to run a mower, especially when the hydraulics don't hold very well.

A manual transmission jumping out of gear is a sign of excessive gear lash. Your transmission bearings need to be replaced before the gears are damaged. This is a BIG job.

most pto operations have a 2 position clutch. Full down to select gears and 1/2 down to release pto when travelling. Check that clutch pedal operation is correct It may need adjusting

The internal parts are damaged.

If your tractor does not have "live pto", then neither the pto shaft, nor lift arms when the clutch is depressed.
I don't think any 2n's, 9n's, or 8n's came equipped with a live pto.
Hope this helped.

Put tractor in highest gear and rock back and forth by hand using rear tires.

Pulls the bolts from the lever cover. You should be able to remove and inspect to see if the fork is busted or shaft it bent. go here for tech help and or parts/ manuals...http://www.just8ns.com/index2.htm

Try it while just coming to a stop.or just starting to move forward.
Depress the clutch and push it back towards engagement position....because it's tied to wheel speed the moving parts might allow it to drop in.