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Posted: 4/22/2014 2:01:26 PM EDT
I recently picked up a gooseneck trailer with a 22' tilt bed, and I am having a few issues with the hydraulics. The trailer uses a 12 volt hydraulic pump and dual hydraulic solenoids, one for lowering and one for raising. It has twin hydraulic cylinders, which look very similar to the hydraulic rams found on your typical log splitter. When I first brought the trailer home, I couldn't get the hydraulics to do anything. Found that the control box was frayed near the hydraulic motor, so I spliced the wires back together. The control box uses four wires for raising/lowering, red, green, white, and black. Once I spliced the wires back together, I still had no hydraulic pressure. The main 12v solenoid for the motor would only click when either button was pressed, so I pulled the solenoid and cleaned all the contacts. I reassembled everything as it was previously wired, and was able to get the rams to raise...but not lower. I am assuming the hydraulic solenoid for lowering simply isn't opening.

Here are a few pics of what I have:












As you can see, none of the stuff was well maintained. The trailer has been sitting out in the open for a couple of years, so there was quite a bit of oxidation. The control box/switch is in rough shape, but seems to be serviceable.

Looking at the hydraulic solenoids, I assume they ground through the case/frame, and the single wires going to each are 12v+ (hot) wires? Does the wiring look correct in the pics? I know both wires appear to be white, but I believe they have been bleached in the sun.

Also, take note of the 12v main solenoid on the motor. The two smaller posts are marked "I" and "S". The "S" post is wired to the switch, whereas the "I" has no wiring. Is this correct? The solenoid is bolted to the top of the motor casing with a single screw, so I am assuming that it is also grounded through the frame.

Any suggestions?
Link Posted: 4/22/2014 2:06:12 PM EDT
The up down control box is definitely toast. I would start there.
Link Posted: 4/22/2014 2:12:40 PM EDT
The up down control box is definitely toast. I would start there.
View Quote


I forgot to mention, when the lowering button is pressed, the motor does run....its just the bed doesn't lower.
Link Posted: 4/22/2014 2:13:02 PM EDT
The two solenoids (lack of better words) that are on the aluminum block with the white wires
coming from them are responsible for letting the cylinders lower.

They open and let the fluid flow back into the reservoir.
If it works the way I think it does, the motor wont run on the down side
Link Posted: 4/22/2014 2:13:53 PM EDT
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Originally Posted By VRMN8R:
The two solenoids (lack of better words) that are on the aluminum block with the white wires
coming from them are responsible for letting the cylinders lower.

They open and let the fluid flow back into the reservoir.
If it works the way I think it does, the motor wont run on the down side
View Quote


Agreed pretty sure it would be gravity down
Link Posted: 4/22/2014 2:17:17 PM EDT
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Originally Posted By 4Kilo12:


Agreed pretty sure it would be gravity down
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Originally Posted By 4Kilo12:
Originally Posted By VRMN8R:
The two solenoids (lack of better words) that are on the aluminum block with the white wires
coming from them are responsible for letting the cylinders lower.

They open and let the fluid flow back into the reservoir.
If it works the way I think it does, the motor wont run on the down side


Agreed pretty sure it would be gravity down
I have a pump and motor that is similar but it only operated one cylinder.
It came from a man lift. When you pushed "down", the solenoid between the tank and
motor opened up and let the fluid flow back.

I would think if you took the white wires and put 12v direct to them, you should hear it click
Link Posted: 4/22/2014 2:19:02 PM EDT
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Originally Posted By 4Kilo12:


Agreed pretty sure it would be gravity down
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Originally Posted By 4Kilo12:
Originally Posted By VRMN8R:
The two solenoids (lack of better words) that are on the aluminum block with the white wires
coming from them are responsible for letting the cylinders lower.

They open and let the fluid flow back into the reservoir.
If it works the way I think it does, the motor wont run on the down side


Agreed pretty sure it would be gravity down

Gravity is quick, prolly need to control it huh?
Link Posted: 4/22/2014 2:20:16 PM EDT
You need an electrician, not a hydraulic guy.
Link Posted: 4/22/2014 2:23:51 PM EDT
[Last Edit: 4/22/2014 2:28:21 PM EDT by bluebus]
Pull the coil off the "down" valve. Put the blade of a screwdriver or something metallic like that inside the coil and press the down button. If the coil is working you should feel the coil pulling on the screwdriver. That should eliminate the coil. If you feel it pulling remove the valve and make sure there is no crap in it.

ETA: if the is only one wire going to the coil you will need to ground it first.
Link Posted: 4/22/2014 2:30:15 PM EDT
[Last Edit: 4/22/2014 2:31:34 PM EDT by Dumpster_Baby]
Holy crap, that's bad. If it was mine I would replace every single electrical doodad except for the pump motor, if the motor / pump actually works. Most all of the wiring is crap, too.

The rest of it - trash can. Solenoids and contactors (relays) do not like rust on the moving parts, especially the moving plunger in the coil. The plungers can stick in the coil bobbin in any position. Tolerances between the plunger and bobbin can vary all over the place, and tight tolerances jam a lot easier.

All the new parts absolutely have to be in waterproof / dust proof boxes. I know, I know, "it worked like it is for 25 years, it's good enough". You either like your stuff to work every time or you like to tinker with your stuff at (usually) the worst time and place. I see a lot of jackleg wiring repairs in that mess. "There, I fixed it".


Link Posted: 4/22/2014 2:53:39 PM EDT
Yeah, its definitely bad!

It amazes me the amount of money people spend on stuff, only to completely neglect it.
Link Posted: 4/22/2014 2:56:07 PM EDT
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Originally Posted By dbort:
You need an electrician, not a hydraulic guy.
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This.

Get a new " box on a leash "... or just replace with up/down toggle switch mounted on tongue somewhere.

Link Posted: 4/22/2014 3:00:50 PM EDT
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Originally Posted By Jason280:
Yeah, its definitely bad!

It amazes me the amount of money people spend on stuff, only to completely neglect it.
View Quote


First thing you learn about equipment is to keep it under cover, pole barn, shed, roof.
Sitting outside in the rain for long periods kill equipment.
Link Posted: 4/22/2014 3:25:41 PM EDT
Link Posted: 4/22/2014 3:27:26 PM EDT
You can check the coils like was mentioned above. But the cartridge could be bent or seized. That is the stem the coil goes around. If you take this out be aware there will be hydraulic pressure behind it. The stem is very week and they bend easy so check that and also when putting the cartridge back in dont over tighten it. It is an O-Ring seal so once it is seated that is it ( not much more than finger tight). If it is an equipment trailer it could be power down meaning the pump should run going down as well. Check the hoses if both seem to be the same type of hose it is probably power down, usually gravity down has much weaker hose on the rod (or ram) end. The cartridge inside usually hangs on those if they have set in the weather and bends if they are not protected well. Good luck.
Link Posted: 4/22/2014 3:36:29 PM EDT
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Originally Posted By Jason280:


I forgot to mention, when the lowering button is pressed, the motor does run....its just the bed doesn't lower.
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Originally Posted By Jason280:
The up down control box is definitely toast. I would start there.


I forgot to mention, when the lowering button is pressed, the motor does run....its just the bed doesn't lower.

You have a miswire then.It's a gravity down solenoid,the motor should not run when you press the down button,it could be the main solenoid,or the broken wire in your pics,or a bad switch,or a miswire,ect.I'd ring the wiring out with a continuity tester before doing anything.
Link Posted: 4/22/2014 3:44:11 PM EDT
You could save yourself quite a bit of money by re wiring this yourself using toggle switches and some wire. Replacement solenoids aren't all that expensive either and can be found at grainger.
Link Posted: 4/22/2014 4:20:49 PM EDT
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Originally Posted By bluebus:

Gravity is quick, prolly need to control it huh?
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Originally Posted By bluebus:
Originally Posted By 4Kilo12:
Originally Posted By VRMN8R:
The two solenoids (lack of better words) that are on the aluminum block with the white wires
coming from them are responsible for letting the cylinders lower.

They open and let the fluid flow back into the reservoir.
If it works the way I think it does, the motor wont run on the down side


Agreed pretty sure it would be gravity down

Gravity is quick, prolly need to control it huh?

It would not be an instant drop.
It takes time for the oil to flow back thorough the hoses into the reservoir, and you are controlling it with the solenoid /valve anyway if you wish to stop the downward movement at any point.

I'm with the guys who think this is a gravity-to-lower system. The pump shouldn't run on the down travel.
If there's only one hydraulic hose running to each cylinder, than that's certainly the case.
The pump pressurizes the base of the cylinder, causing the ram to extend, raising the box.
The load (or the empty dump box's weight) then pushes the ram back into the cylinder, pushing the oil that's in it back into the reservoir (once the pump is shut off and the appropriate valve(s) are opened.)
Link Posted: 4/22/2014 4:23:57 PM EDT
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Originally Posted By bluebus:

Gravity is quick, prolly need to control it huh?
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Originally Posted By bluebus:
Originally Posted By 4Kilo12:
Originally Posted By VRMN8R:
The two solenoids (lack of better words) that are on the aluminum block with the white wires
coming from them are responsible for letting the cylinders lower.

They open and let the fluid flow back into the reservoir.
If it works the way I think it does, the motor wont run on the down side


Agreed pretty sure it would be gravity down

Gravity is quick, prolly need to control it huh?


hence the principal of hyd systems liquid don't compress that easy even on fel's with float its a slow ride down
Link Posted: 4/22/2014 4:45:37 PM EDT
[Last Edit: 4/22/2014 4:55:34 PM EDT by Jason280]
I'll take a few pics of the hydraulic cylinders and hoses tomorrow.

eta: I've been looking through the Monarch website, and it does look like they offer a power-down pump. I haven't been able to find the exact model as mine, but the models with dual solenoids on top do appear to be powered both ways.
Link Posted: 4/22/2014 4:48:29 PM EDT
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Originally Posted By Dumpster_Baby:
Holy crap, that's bad. If it was mine I would replace every single electrical doodad except for the pump motor, if the motor / pump actually works. Most all of the wiring is crap, too.

The rest of it - trash can. Solenoids and contactors (relays) do not like rust on the moving parts, especially the moving plunger in the coil. The plungers can stick in the coil bobbin in any position. Tolerances between the plunger and bobbin can vary all over the place, and tight tolerances jam a lot easier.

All the new parts absolutely have to be in waterproof / dust proof boxes. I know, I know, "it worked like it is for 25 years, it's good enough". You either like your stuff to work every time or you like to tinker with your stuff at (usually) the worst time and place. I see a lot of jackleg wiring repairs in that mess. "There, I fixed it".


View Quote

Sounds like a good starting point.
Link Posted: 4/22/2014 4:54:23 PM EDT
As long as you get power to both coils at opposite times then swap the coils, if nothing changes then swap the stems. You'll find the faulty part. You could ohm each coils out also, I'd guess they would be 20-40 ohms.
Link Posted: 4/22/2014 4:58:44 PM EDT
As long as they are double acting cylinders they may have a lock valve or safety valve. In the event of a hose blowing on the head end of the cylinder the load won't fall. With a lock valve it takes pressure on the rod end to let oil out of the head end, for lack of a better way to put it.
Link Posted: 4/22/2014 5:01:35 PM EDT
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Originally Posted By Jason280:
I'll take a few pics of the hydraulic cylinders and hoses tomorrow.

eta: I've been looking through the Monarch website, and it does look like they offer a power-down pump. I haven't been able to find the exact model as mine, but the models with dual solenoids on top do appear to be powered both ways.
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Pics of the cyls will be the proof
Link Posted: 4/22/2014 5:40:45 PM EDT
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Originally Posted By Jason280:


I forgot to mention, when the lowering button is pressed, the motor does run....its just the bed doesn't lower.
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Originally Posted By Jason280:
The up down control box is definitely toast. I would start there.


I forgot to mention, when the lowering button is pressed, the motor does run....its just the bed doesn't lower.



Look at the Hyd Sol on the left in the close up Picture. The White Wire is Cut.
Link Posted: 4/22/2014 5:53:16 PM EDT
[Last Edit: 4/22/2014 5:54:14 PM EDT by KRONIIK]
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Originally Posted By Wack-A-Mole:



Look at the Hyd Sol on the left in the close up Picture. The White Wire is Cut.
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Originally Posted By Wack-A-Mole:
Originally Posted By Jason280:
The up down control box is definitely toast. I would start there.


I forgot to mention, when the lowering button is pressed, the motor does run....its just the bed doesn't lower.



Look at the Hyd Sol on the left in the close up Picture. The White Wire is Cut.


The insulation is cut, but the wire itself probably has continuity.
But the wiring in general is crap.
Link Posted: 4/23/2014 10:27:52 AM EDT
Ok, I've made a little progress today...

I took the switch apart, and rewired it the best I could. I also pulled both hydraulic solenoids, which turned out to be a small disaster. I pulled the drop solenoid, which allows hydraulic fluid to drain back into the tank when lowering the ram. Of course, like a moron, I removed it while the ram was at highest position....which lead to a damn geyser of hydraulic fluid. Yes, it was my moron moment of the day. Once the bed hit bottom and it stopped flooding fluid, I pulled the remaining solenoid. Now, these two solenoids are not the same...one is "longer" than the other. I bench tested both with a 12v power source, and the longer one worked fine. The drop solenoid did not, so I took it apart and found that the spring had compressed too much. I stretched it a bit, giving it more "spring" action, and now the solenoid clicked/magenetized like it should.

I reassembled everything, added all the hydraulic fluid I had on hand, and was able to get the bed to lift somewhat. I believe it had a lot of air in the system, but I am not sure how you would bleed the set up. I could get it to raise a bit, but it would drop back down with gravity. Not sure if that's simple an air issue, or what. I was able to get it to pump pressure "down", but had to stop testing as the tank is too low on hydraulic fluid. I'm about to head to town and pick up some more, and then continue monkeying with the trailer.

With the rams at their lowest position (bed all the way lowered), how much hydraulic fluid should be in the tank?

Also, I tested the switch with a voltage meter, and the white wire in the pic is ground (-) and the black is (+). The white wire connects to the "S" marked post on the solenoid, and the black wire connects in with the 12v+ lead from the battery. The red and green wires are simply the 12v+ leads to each hydraulic solenoid. I'm just curious if these wires aren't incorrect, at least regarding the white and black. On the other hand, does it really matter? Would it simply reverse the functions of the switch?

Link Posted: 4/23/2014 10:48:58 AM EDT
best way to bleed air is by cracking the fittings slightly while cycling the hydraulics.
Link Posted: 4/23/2014 10:53:22 AM EDT
It doesn't matter how you wire the coils. They need one power coming from the switch and one ground. They just create an electromagnetic field and operate the valve. Polarity doesn't matter there. You can check your coils for continuity and resistance to make sure they're good. Resistance should be similar between the two.

With the bed down it wouldn't hurt to pull those valves and have a look at them. There could be an o-ring or backup ring damaged or displaced. It's also possible to get a little trash in a valve and have it hang up. Look very closely at all the passageways and clean out anything you see. You can operate the valves manually with them removed by pushing up into the middle with a small pick and watching the valve move. It doesn't move much, well less than a quarter inch.

Change the hyd oil too.

PM me if you have any questions. I work on this type of stuff all day long.
Link Posted: 4/23/2014 10:57:50 AM EDT
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Originally Posted By DirtDivision:
best way to bleed air is by cracking the fittings slightly while cycling the hydraulics.
View Quote


I wouldn't do this. It'll work it's way out once everything else is working correctly. Compressed air in hyd lines and components can create a hazardous situation if you go trying to bleed it willy nilly.
Link Posted: 4/23/2014 11:01:33 AM EDT
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Originally Posted By adamtheduke:


I wouldn't do this. It'll work it's way out once everything else is working correctly. Compressed air in hyd lines and components can create a hazardous situation if you go trying to bleed it willy nilly.
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Originally Posted By adamtheduke:
Originally Posted By DirtDivision:
best way to bleed air is by cracking the fittings slightly while cycling the hydraulics.


I wouldn't do this. It'll work it's way out once everything else is working correctly. Compressed air in hyd lines and components can create a hazardous situation if you go trying to bleed it willy nilly.



I'll agree. i guess i should have put a disclaimer. You should really know what you're doing when cracking lines.
Link Posted: 4/23/2014 2:56:04 PM EDT
Ok, quick update.

I seem to have figured it out, at least for the time being. Here are a couple pics of the hydraulic coils:









The shorter of the two was the one not working correctly. I disassembled both, and cleaned them up to ensure correct contact. The longer one tested fine on the bench, but the smaller one wasn't opening/closing correctly. I mentioned I tried "extending" the spring (larger one in the pics), but this made issues worse. I am not sure what the point of the spring is, as it doesn't help the coil whether its long or short. Before I altered it, the coil wasn't working. Once I extended it, it still didn't work. I simply removed it, and the coil correctly opened and closed with 12v. I reinstalled the coils, everything works great now.

The switch is definitely bad, which certainly wasn't helping me with troubleshooting. It works sometimes, sometimes not....there is an issue with the internal contacts when the buttons are depressed. I believe if I could get it apart and clean the contacts, all would be good. Problem is, the plastic housing is in such bad shape that any further disassembly will do more harm than good. My option is to pick one up off eBay for $42 delivered....

...or, I could simply wire up my own. It can't be that difficult. The pump only rotates one direction, and depending on which coil is open, raises or lowers the bed. This particular pump/hydraulic system is not set up to lower with gravity, it is powered both up or down. That being said, the rams will lower without assistance of the pump as long as the correct coil is open to drain fluid into the reservoir. Also, the bed will hold in any position as long as the coils are closed.

All I need to do is wire up two toggle switches, a 2-way and 3-way, and it will serve the same function and give me the option to lower without the use of the pump. The 2-way would simply energize the solenoid to turn the hydraulic pump, and the 3-way would control either hydraulic coil for up/down. Any reason this wouldn't work? I know it would be easier to simply order a switch, but what fun would that be??

Link Posted: 4/23/2014 4:45:04 PM EDT
[Last Edit: 4/23/2014 4:45:31 PM EDT by newguy2k3]
Instead of two toggle switches you can get a dual pole, dual throw switch(I think that is the correct name). It will be a 3 way on-off-on switch with 6 contacts, kinda like 2 3 way switches in one. Use one side to power your coils and the other to power the pump solenoid. On the side you use to control the pump just jump both of the switched on contacts together and run one wire to the solenoid.
Link Posted: 4/23/2014 6:22:00 PM EDT
The only problem I see with changing over to toggle switches is that it won't be exactly the same as the way it was designed to operate. What you have now (minus the black and white jumpers) is two contactors with normally open and normally closed sides. It's set up to keep both coils from operating at the same time, perhaps as a protection for the hydraulic components. The way the normally closed sides of the contactors are jumped right now it isn't protecting anything, but that's the original intent.

My guess is that somewhere along the line the NC side of the contactors quit working (NC are always the first to go) and so they were jumped without asking why they might have been like that in the first place.
Link Posted: 4/23/2014 7:04:42 PM EDT
I see what you mean, but I do like the option of being able to lower the bed simply via gravity (and not running the pump). Question is, any reason this might cause damage?
Link Posted: 4/23/2014 7:17:39 PM EDT
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By Jason280:
I see what you mean, but I do like the option of being able to lower the bed simply via gravity (and not running the pump). Question is, any reason this might cause damage?
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That wouldn't cause damage. Opening both valves with the pump running might, thus the NC sides of the contactors. If you want it to lower by gravity only you could always rig a switch to interrupt the signal to the motor contact solenoid.
Link Posted: 4/23/2014 7:20:27 PM EDT
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Originally Posted By Jason280:
I see what you mean, but I do like the option of being able to lower the bed simply via gravity (and not running the pump). Question is, any reason this might cause damage?
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Power down is nice if you have something heavy on the back and can't get enough weight on the front.
Link Posted: 4/24/2014 7:01:33 AM EDT
I guess I have to decide if I want to use the factory style plug, or wire in my own. The factory plug does make things a lot easier/simpler, but I do like having the option of lowering the bed without the use of the hydraulic pump.
Link Posted: 4/24/2014 7:15:14 AM EDT
Another consideration if you lower the bed without running the pump, depending on the valving, it may not be able to pull oil into the rod end when lowering. That would cause air and cavitation in the system and my cause it to blow oil out of the tank.
Link Posted: 4/24/2014 7:51:04 PM EDT
Another consideration if you lower the bed without running the pump, depending on the valving, it may not be able to pull oil into the rod end when lowering. That would cause air and cavitation in the system and my cause it to blow oil out of the tank.
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How would I determine if this is the case with my system?
Link Posted: 4/24/2014 8:00:06 PM EDT
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Originally Posted By newguy2k3:
Another consideration if you lower the bed without running the pump, depending on the valving, it may not be able to pull oil into the rod end when lowering. That would cause air and cavitation in the system and my cause it to blow oil out of the tank.
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99% of the time these systems are gravity down .. no pump running and the button pushed for down is simply opening the closed solenoid relieving pressure from the bottom end of the ram. EXACTLY how the solenoids on almost ALL plows work.. pump on- solenoid open it lifts up.. pump off solenoid opens goes down, with some fancy electronics that allow the solenoid to stay open for float function


id be certainly shocked if this one had pump running for down function..
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