Forgive me for lacking knowledge on this however my dad has asked me to try research information on lost hydraulics in his 70's JD 7520. I decided to try here since I can't find much directly online. This is what Im told him or know: since he got the machine hydraulic pressure wasn't always present upon startup......often times he would start the tractor and wait up to a minute for hydraulic pressure.to show....in fact at times the whole machine would jolt and the steering wheel and machine would pivot/move significantly when pressure appeared. Fast forward to a couple weeks ago......he was cultivating when all pressure was lost. No steering, no clutch, nothing to the rear hoses/couldn't lift the cultivator. He's asked mechanics locally but most don't know this machine specifically so now we are in search of an OEM service manual to try find if there is troubleshooting tips or pics of hydraulic system or secondary hydraulic pump info.... anything that could help lead to a solution. Any advice out there?