Just picked up a JD 690B at auction and I don't have any history on it. I'd guess it's an early 70's model. I'm having troubles with the thumb - it doesn't work. According to the hydraulic's company I took the valve to, the valve works fine and the plumbing to it is all screwed up. The valve requires a lower-than-pump pressure connected to the pilot port. The machine puts out about 1500 psi. and they said I should have a line coming from a pressure reducing valve to the pilot port on the valve of somewhere between 300-500psi. The problem is I can't find any hydraulic lines anywhere that put out anything less than 1500psi. My Tech Reference manual shows pictures of a 'pilot pressure reducing valve' but I don't appear to have anything like that on my rig. Is there anyone out there who has a JD 690B with a thumb? I could use some advice or even pictures of your plumbing.
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