i have a 1966 John Deere 4020 PS diesel the tractro starts easy and runs well. the hydraulics work in D only. if i select L or LD no hydraulics at all but in D the 3 point raises and lowers quickly. the FEL works if i manipulate the levers in a specific sequence (eg scv lever forward + loader lever back = loader raises , scv lever back + loader lever forward = loader lowers). Power steering and brakes perform flawless no trouble whatsoever. trans temp rises after 3 hours or so of brushhogging
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L/D mechanism needs to be adjusted following the steps outlined in JD tech manual. It also sounds as if SCV needs attention & it's valves set to spec's as FEL should operate correctly with scv lever in either forward or rearward position but not both positions. I will suggest to attach loader hyd's directly to tractor hyd's freeing scv's for other purposes.