Hi, I recently purchased a 1999 JLG 450a that has a few issues. First is the steering does not work. I replaced the joystick and verified that I am getting voltage down at the coil when I try to turn. The second issue is the boom intermittently does not want to raise or lower. Similar to the steering I am able to see voltage down at the coils when I move the controls from the basket. I am thinking it's a hydraulic issue but I'm new to hydraulics and don't know where to start. One other thing to note is the drive and swing functions work. Not sure if that helps but thought it might be useful. Any help would be greatly appreciated.
Maybe this will help: HeavyEquipmentForums Both symptoms point toward a common hydraulic/control issue on the main function manifold rather than the joysticks, since you have coil voltage and other functions (drive/swing) work. Given this model and your symptoms, the most common causes are: Main function “dump” / master solenoid not opening fully or sticking intermittently. Low system pressure or flow due to clogged return filter or suction strainer. Stuck or contaminated section spools in the lift and steer valve sections. Poor ground or weak power to coils under load, even though you see voltage at rest. Because drive and swing work, the pump and engine are likely OK, and the problem is local to the boom/steer control manifold or its supply. Step 1 – Verify hydraulic Check oil level and type in tank; top up if even slightly low. Inspect and, if unknown age, replace the return filter element. Look in the tank (through fill/inspection) while someone operates lift/steer; look for heavy aeration/cavitation. Listen for pump whine when trying to steer or lift; loud cavitation suggests suction blockage or low oil. Step 2 – Confirm the main dump / enable valve Locate the main control/dump solenoid on the valve block (refer to the 450A service/hydraulic manual for exact location and ID number). With an assistant commanding steer or lift, verify: You have battery voltage at the dump coil when any platform function is called. The coil is magnetizing (screwdriver test on the nut) and the valve body shows a slight change in sound/feel. If voltage and magnetism are present but steer/lift still dead/intermittent, pull that valve cartridge, inspect for debris or scoring, clean it and the bore, or replace if questionable. Step 3 – Test steer and lift Since you already see voltage at the coils, next check whether the valve sections are actually shifting and making pressure. Steer: While commanding left/right, feel the steer valve section; you should feel/see some reaction in the hoses and hear a slight change in tone. Check whether the steer cylinder tries to move or hoses go firm; if no reaction, crack a work-port line briefly (with proper PPE, engine at idle) and see if there is flow when you energize steer. If there is no flow under command but other functions work, the steer spool or its solenoid cartridge is likely stuck or blocked. Boom lift: Do the same crack-test on a lift cylinder port or use the test port for main lift pressure if provided in the manual. If pressure/flow is absent or erratic only when operating lift, pull and clean the lift section’s control valve cartridges. Contamination in older machines is very common and can cause exactly this intermittent behavior. Step 4 – checks electric under load Even though you see voltage at the coils, verify the circuit integrity under load. Measure voltage directly at the solenoid coil while someone fully strokes the joystick; ensure it stays close to battery voltage and does not collapse. Check the main ground point for the valve bank; clean and tighten all ground and power connections feeding the platform and base control logic. Inspect the harness plugs at the turntable junction/manifold for corrosion, broken pins, or pulled wires, especially for the lift and steer outputs. A weak ground or corroded connector can give a “nice” voltage reading with a meter but not allow enough current to shift the valve. If it is still, then the 450A service manuals contain good troubleshooting trees and the hydraulic schematic for lift/steer circuits. If steer and lift are solid from the base but not from the basket, focus on platform controls, wiring, or platform enable logic.
Thanks for the reply. I will check that out this week and see what I find.
Sorry for the delay in response. It's been a while since I've been able to get outside and work. Thank you for your earlier reply. I replaced the dump valve and things are working better. I can now steer and drive consistently. I am now trying to figure out some other issues. The basket doesn't rotate or level, the telescope doesn't go in or out, and the main boom doesn't go up or down. I'm wondering if it's issues with the cartridges for those functions. I tested the coils again and they all seemed fine. Any advice on where to look would be appreciated.
I'm also wondering if there's maybe another common hydraulic component that could be causing the issue since there are still multiple functions not working. Is there anything other than the dump valve that could affect those functions?
Sorry for all the follow ups but I was wondering if the part I have circled is the proportion control valve for the bang functions? I am going to test that out tomorrow if it is.
Umm, bang bang functions do not have a "proportional control". Being bang bang control, meaning, pretty much, full on or full off, is self defining. There in nothing proportional with bang controls. Is this an AI thread or something???
No sorry I'm just getting myself confused. I thought I saw a proportional valve mentioned in another thead.
Point taken. And you may be legit, it's just hard to judge now days with AI everywhere. And I don't know the answer to your problem, and hope you find a resolution here.
Hi Willie59, I think where I was getting confused is here you mentioned a proportional flow control valve. Is that located somewhere in the diagram I sent above?
Umm, not in this thread, maybe in another as I respond to so many threads it's not possible for me to keep track. But for the sake of the discussion, bang functions are just that, full on or full off, typically toggle switch control. Proportional, that's control that works like the throttle pedal on a vehicle, function speed is determined by how much you move the throttle pedal. I hope this clears this up.
I had a good learning day today but no fix yet. I was able to get all the functions working when I tried them at the same time as a previously working function. Next I swapped the bang bang and swing flow control cartridges which didn't help. I then checked the voltage at the bang bang flow control coil and that looked good even for the functions that aren't working. Then I swapped the flow control coils which also didn't help. Next I swapped the sequence cartridges and that didn't work either. I'm thinking the only thing left is to try the load sensing shuttle valve. I didn't have the right size Allen wrench to try it so I'll get one tomorrow and try that next. If anyone has any other ideas or anything I missed feel free to let me know.
Something else I noticed today is the swing works both ways from the ground but only swings to the right from the platform. I'm not sure that it's related since everything else works the same from the ground and from the platform.
What's the machine serial number? What engine? What functions have proportional joysticks and which one's use toggle switch control? Is there a speed control knob at the platform for the toggle controls?
The serial number is 1000252 0300044220. It's got a Duetz engine. The only functions with a proportional joystick are the swing and lift/telescope. There is a speed control knob at the platform for toggle controls
Just to clarify, a 450A has two booms, upper and lower, are both of those booms proportional control?
It's for the upper lift. The lower lift is controlled by a toggle switch and that works all the time.
Got it. Assuming I'm looking at the correct service manual #3120750, drive/steer joystick is on the right and swing/upper boom joystick is on the left, lower boom (tower) is toggle switch control with speed controlled by proportional speed control knob.
The manual you sent is the correct one and the diagram and everything you said is accurate.
Ok, I see what you're working with. Not going to promise anything, but I'll noodle into this, but I am busy with other things. On top of that, the troubles you describe are those that are very hard to troubleshoot over the internet. But I will do a little digging and see if something jumps out at me. Maybe so, maybe not.
Thanks Willie59. I'll keep playing around over the next few days and see what else I can find out. I really appreciate your help.
Hi willie59, I just wanted to let you know I figured out the telescope issue, the cartridge is bad. I swapped it with the tower cartridge and the telescope started working fine and the tower stopped working. I'm thinking maybe the cartridges for the platform level, rotate, and the upper boom could also be bad. I am going to order some parts tonight and see how it goes. Let me know if you think of anything in the meantime.
A quick look at the hydraulic schematics for your model, the drive has it's own variable displacement pump that works only drive. All other functions operate via two fixed displacement pumps, likely gear pumps. Pump 1 operates swing and upper boom. All boom functions work using 4 way directional control valves that are bang valves, again, full off or full on, for direction, i.e., up/down, left/right. For proportional control the functions also use a proportional solenoid valve. So take upper boom up. When you hit that toggle you power the boom up solenoid on the 4 way valve and also power up the proportional valve to control how much oil flows through that circuit. The swing has its own proportional valve, all other functions share the same proportional valve controlled by the speed knob on the platform. Pump 2 controls steer and all other boom functions. What makes pump 2 circuit different is it does use a dump valve that must be powered up for functions to work. You mentioned having a steer problem, replaced the dump valve, and now steer works. Ok, sounds logical, but that tells us that if you still have problems with lower boom, telescope, etc, it's not the dump valve, you fixed that. So let's say you wish to operate lower boom. That requires power up the dump valve, power up the directional solenoid for lower boom up or down, and power up the proportional valve for pump 2 circuit controlled by the speed knob. That's 3 different things that have to happen. Here's where it gets more interesting, the bang valve, that's full voltage (12V nom) when you power them up, easy to check with a volt meter. The proportional valves, not so easy. Proportional control on those machines use what's known as Pulse Width Modulation (PWM) signal to the coils. PWM is a voltage signal of full on, then full off, then full on, full off, repeating. Full on voltage typically ranges between 5 to 9 volts depending on the design. That on/off/on/off, that's the pulse. The width is the duration of time between full on/off. A quick/short burst of full on/off only opens the solenoid a little, slow speed. A longer, wide burst of on/off opens the solenoid more, higher function speed. And this change of pulse from little to great runs the full sweep, that's why it's called proportional. But the thing about PWM is you cannot see it on a volt meter, you will only see the full on voltage, but you won't see the pulse, that would require an oscilloscope, so troubleshooting a PWM proportional circuit doesn't work with a volt meter.
Looks like you replied while I was posting.
You should be able to read the duty cycle on a PWM circuit with a volt meter that reads duty cycle, but I agree the best way to look at a PWM circuit is with an oscilloscope. Checking duty cycle would show if there is activity and if it is changing but would not show you the quality of the wave form.
Hey guys, I made some good progress this week. I found out the lower and upper boom cartridges had been switched prior to me buying the lift. Once I put those in the right spots everything works from the ground control. The only things not working now is the platform level from the platform and the upper boom raising and lowering from the platform. I think both these issues are related to the platform level somehow. Something else odd that I noticed is that when I raise the upper boom from the ground the platform will tilt up and when I lower the upper boom the platform will tilt down. Is this expected behavior? It seems backwards to me since it would dump you out of the platform when lowering or raising. Any ideas on where to look would be helpful. I will do some reading in the meantime and see what I find.
For some crazy reason JLG made the upper boom/platform leveling circuit on those machines very complicated. Most aerial lifts use a more simplified system by having a cylinder to control the upper boom, then a separate circuit using a master cylinder and slave cylinder to operate platform leveling, the two circuits are independent of each other. Not on that machine, the upper boom circuit and leveling circuit are part of the same circuit using several solenoid valves to make one go up while the other goes down and vice versa. The fact that yours is operating backwards indicates that the same jackweed that swapped the lower and upper boom cartridges didn't stop there, they mucked up the upper boom/leveling circuit as well. I wouldn't know where to start troubleshooting that over the internet.
Is there a sensor that enables or disables the level switch from the platform? Also is there a sensor that controls the auto leveling? Or is the auto leveling just proportional to the height of the upper boom?
No, it's way more complex than that. I took a quick look at the hydraulic diagrams, and I've been working on aerial machines for over 40 years, just not this model. When I saw what I saw, my head started spinning. To fix this is going to require you to endure a crash course in understanding hydraulic controls as well as reading the schematics, and that applies to the electrical as well, because both are happening when you raise/lower the upper boom and how it relates to platform leveling. It's a very complex process in operation. Obviously, someone has got something hooked up wrong, either in the hydraulic side of the electrical side. The question is where. That's going to be a bear to noodle out.
I started looking at the hydraulic diagrams and I have a question. In the picture it looks like lines LC and LR control the upper boom. Should LC make the boom extend?
LC extends the upper boom cylinder, raises upper boom. LR retracts the upper boom cylinder, lowers upper boom. B1 retracts the platform leveling cylinder, makes platform level down, B2 extends the platform cylinder, makes platform level up. Those letter, LC, LR, etc, should match letters stamped in the control valve main manifold adjacent to the respective hose connections. Port LC on the main manifold should have the hose connection that goes to the port on the extend side of the upper boom cylinder.
Great thanks that's what I thought. I think someone switched the coils for the upper boom and swapped the LC and LR hose connections at the manifold. What I'm seeing is that LR will raise the upper boom and LC is lowering the upper boom. I'm going to put the coils and the hoses back in the right places tomorrow and see if that helps.
No, look again, LR retracts the upper boom cylinder, which would make the boom go down, lower it. LC extends the upper boom cylinder, which would make the boom go up, raise boom. On things like this, where things are wonky and there's no obvious reason why, have to figure out why, I always start at the lower controls, forget about the platform controls. Get things working properly from the lower controls, then move to the upper controls. First, when you work the toggle at lower controls, does it work correctly? When you select raise boom, does it raise the upper boom? and when you select to lower boom, does it lower the upper boom? Second, when you work the toggle for platform level up, does the platform go up? When you select platform level down, does it go down?
Is there a diagram anywhere that shows which position the coils are supposed to be in? For example if the upper boom up coil should be closer to the manifold or further from the manifold.
The parts manual would likely have a diagram of the various main control valve components and where they're located on the manifold, but it wouldn't identify which stacked coils did which direction of a function.
Sorry I skipped over this. At the lower controls, when I select raise boom, it will raise the boom up but at the same time it will tilt the platform up. When I select lower boom it will lower the boom but it will tilt the platform down. When i select platform up the platform will go up. When I select platform down the platform will go down. The only thing that isn't working as I'd expect is the platform auto-level when raising or lowering the boom.
Ok, that's key information there. The toggle for platform level works correctly at the lower controls, at least in theory. This is where it gets complicated. Pump 1 (P1) controls upper boom raise and lower, and the circuits for upper boom and platform level are combined, one affects the other. But when you are only selecting platform level, either up or down, that's controlled by P2. To make that happen you have to power up the dump valve for P2 circuit, and to level up you have to power up the platform level up solenoid. To level down, you have to power up the P2 dump valve and the level down/up solenoid, a different solenoid. That's three different solenoid valves that have to be powered up in a certain sequence to operate platform level up/down. And that is working correctly from your lower controls. My point, we already know some idiot who has no business working on these machines has had their hand at yours, but for them to swap everything for this operation, level up/down and it still work correctly, that would be above the most professional idiot level for that to happen. It more likely indicated everything for platform leveling is correct. So, with all that mind bending, we're going to assume they mucked up the upper boom up/down circuit. And here's what we're going to do, and keep our fingers crossed. Swap hose connections at ports LC and LR at main control manifold. Operate the upper boom down toggle, boom should go up, yeah you read that right, and platform should level down as the boom goes up. If that works, select upper boom up toggle, boom should go down and platform should level up as the boom goes down. If that works, then swap the stacked coils on the upper boom cartridge valve. That will correct the toggle being backwards.
willie59, your suggestion worked! I swapped the LC and LR hose connections along with the upper boom coils and things started working normally. At this point everything is working as it should. Thanks everyone for all your help!
Good news indeed. Sometimes you just have to be smarter than an idiot, which is not always easy, and no doubt one has had their hands on your machine. I've been untangling their mess for over 40 years. And it really helps having good diagrams.