Do you know the model of the tractor? International Harvester Company was in business in various forms for over 150 years. If you don't know the model, a picture of the tractor might help. Does your tractor have a draft control lever in addition to the raise/lower lever for the three point? Reason I ask is that on my 574, if the draft control lever is all the way up, the three point won't lower when you use the raise/lower lever. If that isn't the case, then the control valves for the three point might be bad, or the hydraulic pump could be shot. Our 574 had issues where the o-rings in the control block for the three point would fail and then the lift wouldn't work properly. Usually it would just jump when trying to lift anything, not being able to hold it steady. Have you tried using the remote hydraulic outlets (if there are any)? If you haven't, try and see if they work. If not, then the hydraulic pump is probably bad. Low oil levels can cause the pump to suck air and cavitate, damaging the pump and making it leak internally. I'd also check the hydraulic filter or screen and make sure it isn't plugged.
'76 IH 1066 Turbo Diesel, '73 IH 766 Diesel, '72 IH 574 Utility Gas, '56 IH 350 Utility Gas, '47 Farmall H Gas, '08 Bobcat Toolcat 5600 Turbo
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Stihl, Ariens, Tecumseh, LCT, Lauson, Kohler, Subaru and Lawn Boy Certified Technician with over 10 years experience.