OFF
Senior Member
Komatsumech, if you use the private message feature to send me an email address, I'll send you the manual set. That might be a good place to start.
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The JLG 40F Boom Lift Dilemma
- Thread starter od1
- Start date
OFF
Senior Member
Welcome DR.LS, I can send you a copy of the 40F manuals in PDF format, all I need is an email address. You will be able to private message me your email after you've made 3 posts on the forum.
Your swing brake problem could be as easy as adjustment. It is spring applied/hydraulically released. The spring that does the holding is a series of wavy washers inside the barrel of the little hydraulic cylinder. They do break or flatten out sometimes. In an open area, working with someone you trust, raise and block the boom so it can't come down. Have your helper operate the swing function from the ground controls, while you adjust the pads up until they just almost touch (about 0.020).
(first make sure the caliper mechanism moves freely of course). If after the adjustment if brake works, great. if it doesn't grip, you have weak spring washers. They are called "Belleville Washers" and should be available places other than JLG.
Edit: the washers could have also been stacked/assembled wrong by someone in the past who didn't understand their function. Worth checking.
Your swing brake problem could be as easy as adjustment. It is spring applied/hydraulically released. The spring that does the holding is a series of wavy washers inside the barrel of the little hydraulic cylinder. They do break or flatten out sometimes. In an open area, working with someone you trust, raise and block the boom so it can't come down. Have your helper operate the swing function from the ground controls, while you adjust the pads up until they just almost touch (about 0.020).
(first make sure the caliper mechanism moves freely of course). If after the adjustment if brake works, great. if it doesn't grip, you have weak spring washers. They are called "Belleville Washers" and should be available places other than JLG.
Edit: the washers could have also been stacked/assembled wrong by someone in the past who didn't understand their function. Worth checking.
Last edited:
sportnatic
New Member
JLG 40F manual
I need a JLG 40F manual . Have not found one anywhere. Was hoping someone had a copy I could download
I need a JLG 40F manual . Have not found one anywhere. Was hoping someone had a copy I could download
OFF
Senior Member
Welcome sportnatic! Yes, we have a set of 40F manuals in PDF format that I'd gladly share with you. Just make one more post to unlock the private message feature and then private message me an email address I can send the files to.
OFF
Senior Member
Well, two things could be causing it. The cylinder has a "holding valve" on it. Also called a "lock valve". It looks like a rectangular metal block bolted to the cylinder near where the hoses are attached. These lock valves can leak.
The second thing is that a hydraulic cylinder can leak internally without have any evidence of an external leak. The oil pressure just seeps past the piston seals from one side of the cylinder to the other.
sportnatic
New Member
willie59
Administrator
DR.LS, that's not a "I hate to feel stupid" thing, that's actually a funky cylinder. It's been a long long time since I've done one, but I recall they have belleville washers inside loading the piston to push the cylinder out. If I recall correctly, you have to "cage" the rod/piston before you screw the head of the cylinder out, otherwise it will come unglued on ya when you screw that head out. OFF can most likely confirm this. 
OFF
Senior Member
DR.LS, you are correct. Those 2 holes are what you use to unscrew the top out of the cylinder. The tool used for that is called a "spanner wrench" or "pin spanner wrench" or "adjustable pin spanner wrench".
I think what I used to do is put the cylinder in a big vice so that the vice pushed the rod and then unscrewed the cylinder gland, then released the cylinder.
OFF
Senior Member
Welcome Falcon81, I'll get a set of manuals emailed to you today when I get home from work.
Hello everyone, newbie here. I have what I believe to be a JLG 40G 2WD with a Wisconsin MVH4D air cooled engine that I recently rebuilt. I've finally been able to power up the lift and start working on the mess of electrical wires and hydraulics. I was googling the internet and came across this forum and am just amazed at the amount of information I've learned already. It would sure be handy to have some service manuals and/or electrical/hydraulic schematics that are floating around. I hope to post some pics and certainly more questions in the near future. It's nice to know there is a support community for these old dinosaurs.
OFF
Senior Member
Hello everyone, newbie here. I have what I believe to be a JLG 40G 2WD with a Wisconsin MVH4D air cooled engine that I recently rebuilt. I've finally been able to power up the lift and start working on the mess of electrical wires and hydraulics. I was googling the internet and came across this forum and am just amazed at the amount of information I've learned already. It would sure be handy to have some service manuals and/or electrical/hydraulic schematics that are floating around. I hope to post some pics and certainly more questions in the near future. It's nice to know there is a support community for these old dinosaurs.
Welcome Dwor, the 40G was a model JLG made for a relatively short time between the "F" series and the "H" series. The company I worked for back in about 1982 had a pair of 40G's. Unfortunately I threw out all the 40G manuals and schematics I had when I cleaned out my toolbox about 20 years ago. From what I remember they were first generation PQ controllers on Racine valves and very similar in wiring to the 40F. The thing I remember most about them is the sliding hood. I can send you 40F stuff, that's all we've found at this point. Might be something more out there. There has been mention on this forum of a 60G also.
Thank you so much. The 40F info would be much appreciated. From browsing the forum, I recognize a lot of similarities between the 40F info and pics posted and my 40G beast. I've been reverse engineering some electrical and hydraulic schematics just so I can wrap my head around what might be going on with my lift, and just in case I end up ripping the old harnesses out and replacing it. They are indeed Racines. I would like to know more about how those PQ controllers are wired and/or work in term of electrical signal.:bash
OFF
Senior Member
1 more post will unlock the private message feature and you'll be able to send me your email. I'll send you the 40F manuals.
The proportional valves work on the principal that they are always centered. When centered there is no flow to either direction of that function. A coil the valve is hooked to the controller with 2 wires. Testing those wires at the controller (or valve) with a volt meter will show approx. 6 volts once you move the controller enough to turn on the micro switched power. Moving the controller in one direction will increase the voltage to approx. 10 volts, moving the controller in the other direction will decrease the voltage to approx. 2 volts. This change in voltage influences the spool to move off center and supply oil where you want it. Voltage sweep is smooth and steady on a good controller, jumpy and full of dead spots on a bad controller.
I love learning theory of operation:thumbsup. That way you can apply the knowledge to an almost infinite number of problem scenarios. Are schematics of the PQ's in the manuals and are replacement controllers still available? I think mine are "jumpy", or even an all or nothing/on and off action. I'm wondering if these can be electronically serviced….the circuit looks relatively simple, i.e. no integrated circuits or micro parts.