Rebuilt the entire control valve stack as it was needed after one of the valves had a snapped bolt on the bottom and was causing what I think was the relief valve to leak. I'd reassembled the valves, surgically clean, the only big discrepancies being on 3 of them, id machined 3 new "plates" - 8x3mm discs that slide in a channel to block an orifice on either the valve or the one adjacent. Anyway, made 3 new ones as cat said they couldn't get me any within a month or so. Everything back together, no leaks, great. But as seen in video, all hydraulic circuits are weak - to a certain point of pressure, they will "give out". Unlikely to be a main relief valve as that wasn't messed with at all, but thinking it's an internal leak from high pressure to return side? I trying to get service manuals/schematics from SIS but that won't let me pay for the subscription needed.. next steps that I know of are that and to start pressure testing at various spots. May also take a thermal imager and see which line the fluid is returning via..At least by touch, the two smaller of the 3 lines into the inlet valve were hottest. Any other ideas as to what causes this?
Please post a Serial Number to identify schematics, etc.
Ah sorry I should have known to Include that It's RKY02288
Following up -- Seems like the dimensions of the little steel discs i'd cloned weren't "quite perfect", not allowing for a perfect seal. These 'mystery discs' as referred to above are shuttle check valves that fork the load sense line to each circuit. I'm guessing that imperfect seal there somehow lead to the pump not supplying pressure to support the load, which is why it would just 'give out'. Also made sense that one of the lines out of the inlet was hottest here as one is a load sense line. Finally got cat-proper replacements, and she's digging like new again. Anyway - lesson is, when self-fabricating parts for a hydraulic system, it's not "close enough", "dang close", or even "pretty much there" that counts for tolerances - it's "bang on to the ten thousandth". Thanks a bunch, @Nige for the help here
Yep, "good enough for this class of agriculture" doesn't work too well with hydraulic system components.