It could possibly be relief valve. How do you know the pump is working? Did you do a pressure check? Do you have a front loader or just the three point? It may sound dumb, but how's the fluid level?
Pettibone, Ford, Massey Ferguson, International, JD, David Bradley, home mades
Put it in neutral and turn pto ON because a jubilee is like an 8n. But the pump on a jubilee is external. Could be trash in check valve. Could have a bad ring on lift piston. Old ones were leather so if it's not been in use lately...