Another 40F
I have used my JLG 40F for some projects, and now it's for sale, since a local guy wanted to get rid of his 4wd lift. The 40F is amazingly solid and well built, to me. As with any low priced machine, there are a few little things to fix, but the new parts are worth close to what i'm asking, $2750 in Florida, with help loading/driving onto truck.
Anyway, one of the things I've been wondering about is why sometimes I have to blip a function, such as platform level, in order to get the swing or lift function to work. The valves for all the proportional functions were replaced with new bang bang valves in a parallel D5 block, (I still have the proportional controls, but there was a leak and nobody in my small town wanted to fix them). The pressure filter was similarly unknown to my NAPA store and my local hydraulic shop, so I put in a generic25 gpm return filter instead. I have thought that there might be some back pressure that is tending to hold the holding valves, which is relieved when I blip another function on the same dump valve. Or is it the dump valve leaking?
You guys really know your stuff, and I'm just a farm handyman. I have an expensive copy of the JLG manual, but it leaves a lot out, and like you said, has some very challenging small print in the electrical schematic!
I have learned a lot from reading here, and want to thank those knowledgeable folks who contribute their time to this publicly accessible forum. The internet was originally conceived for this kind of research, I think, although they may not have envisioned heavy equipment at first!