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Crawlers, Dozers, Loaders & Backhoes Discussion Forum


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02-12-2014 13:42:21

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Reading everything so far, if your only getting 100 psi to the rod/up end then something is dumping off the flow and pressure. I see where you've changed a relief already, but it sounds to me like there is another relief in the system that's dumping off the pressure to just that one side. I say this because most loaders have what they call a 'port relief' the up and down sides of the system. They do this on the up side to eliminate excessive shock loads on the system should something get dropped into the bucket. If you've got a parts book, or service book, check and see if it shows anything, as that sounds to me like your problem. Good luck and let us know what you find.

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Kevin Wright

02-13-2014 07:52:18

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 Re: GEHL HL4400 BUCKET GOES DOWN BUT NOT UP in reply to NCWayne, 02-12-2014 13:42:21  
there is self leveling circuit that is tied into the bucket control side of the control valve, it consist of a self leveling bypass valve and a self leveling relive valve. i wish i could put a picture on here of what the control valve looks like. its extremely complicated to explain and understand what happens in a given scenario (where fluid is traveling when the self leveling circuit is operating). yes it seems that fluid is being dumped when you try to curl the bucket but im not sure where, i have changed both the bypass, and the relief valves one at a time from a parts machine, i have also changed the entire control valve from that machine to see if it might have been something internal that was causing weak, or bypassed fluid pressure. there is one solenoid that blocks fluid travel on the down side of the left boom cylinder when the key is off, or there is no weight in the seat. it does not affect the bucket hydraulics however. Other problem is most parts are unavailable for this machine i guess because of age mostly. i have no way to test these relief valves to know if they are in good order. the book specifies one as 1000 psi and the other at 1200 but i cant tell which is which. they both appear to be fine by visual inspection, spring looks good, ball seats fine, cant blow air through them so they seem tight but i cant test at what pressure they open...

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02-13-2014 09:36:11

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 Re: GEHL HL4400 BUCKET GOES DOWN BUT NOT UP in reply to Kevin Wright, 02-13-2014 07:52:18  
Just found a parts manual online for your machine. I didn"t see the relief valves you were looking for, but the pressures you give for them being around 1000 psi seems way too low for the actual port reliefs for the various functions. Usually the pressures on these machines is closer to 2500 psi. That said, take a look at the parts book at the link. I don"t know what your serial number is, but take a look at the picture and parts list on pages 25-26. According to the parts sheet number 14 is a relief valve tube. I"m assuming that means there is a relief valve either in that tube or attached somehow to that tube. On the roll forward side it looks like the relief is part number 5.

I work on equipment like this for a living and to me, like I said, the reliefs in the circuit your talking about seem to have way too low of a pressure setting to effect the function your having problems with. Beyond that the only other suggestion I can give is to start at the cylinder and tee into the line and check pressures there. If it"s high enough then backtrack the system and check it at ever point possible until you find the problem. You should find that the hoses going to the cylinders on both sides eventually Tee back together and have only one port off the valve. Somewhere between the valve and the cylinder should be a port relief that acts to dump pressure even if the valve is in the closed position. In other words if you can tee in directly at the valve port and get high pressure, and aren't getting it at the cylinder, that will help pinpoint the problem.

Wish I could help out more but it"s hard to troubleshoot something like this without actually having the machine in front of me. That said, now that I"ve got a parts diagram in front of me it makes things a lot easier. If you run into any more problems and can possibly post pics of the part/area your checking it will make things a lot easier.

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Kevin Wright

02-13-2014 10:00:56

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 Re: GEHL HL4400 BUCKET GOES DOWN BUT NOT UP in reply to NCWayne, 02-13-2014 09:36:11  

the serial # is 3050. it has the ford engine. the number 14 you talk about is the tee in the line where the two lines split coming out of the bypass relief valve which is number 5 on that same page, and go to the left and right cylinders. i put a 3000 psi gauge on right there and that's where i only got 100 or so psi. in the shop manual i have, in the trouble shooting for the loader the only issues it talks about is if the bucket drifts down. it says check the pressure at rear port of tilt cylinders (which is bucket down)if less than 1200 psi to replace the self leveling relief valve. other option is leakage in self leveling by pass valve, says inspect seat and replace valve if defective. the self leveling bypass valve is a sealed unit, the seat is inside and it just looks like a real big plug that goes in the cast iron housing (number 5 on page 27 of the parts book) the book explains nothing about that valve other than where it goes and has an arrow pointing to it on the illustration of the control valve.

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02-13-2014 14:00:08

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 Re: GEHL HL4400 BUCKET GOES DOWN BUT NOT UP in reply to Kevin Wright, 02-13-2014 10:00:56  
Ok, I understand that you can roll the bucket forward and raise the machine, and it still has lift capability, at least for what you were picking when you noticed the problem, but looking at the pics of the machine both of those functions work off the butt end of the cylinder, which is going to create the most cylinder force for a given system pressure. Now, given that the roll back function on the bucket is accomplished by the weak/rod end of the cylinder, and the mechanical linkage involved in the link to the bucket, I'd any problem with the system pressure being low would more than likely show up there first. Given all of that, my next question is this. Even though, based on the pic, pressure actually comes from a single section gear pump -vs- the actual tandem, piston, hydrostat pump, what is the pressure going into the valve where your pic says 'hose from tandem pump'?. Regardless of what they call anything, this should be full system pressure and read such on a gage when you actuate a function and bottom the cylinder out. Try it with all functions (bucket up/down, tilt down/up) and see if there is any difference. Barring a port relief set lower than the system relief (they are usually higher) you should read the same pressure on every function. This will tell you if the problem might be with the pump itself, and will help you truly isolate the problem to a single function or the system as a whole (which would more than likely be the pump going/gone bad). That said I can now see the 1200 psi settings in this system simply because of the cast fittings being used (more like low pressure farm tractor setup than a more modern skid steer running at 2500 to 3000 psi plus), and if the manual says that's all the pressure your supposed to get, then go with that for the reading to look for.

To check the relief valve in your pic by itself, put it in it's housing and cap off everything but a supply line and the discharge line. Run the discharge line to a return/bucket, and pressurize the supply side. If it were me I'd probably fill the supply lines with oil and then use the pump off my Enerpac rams to build the required pressure to see when the valve popped. If you don't have anything like that, you could use an aux port on another tractor to check it up to at least the pressure built by that system. Given that most of them are going to at least operate over 100 psi it should give you at least some idea as to the setting over and above the 100 psi you've tested so far.

Before you go any further I'd check the pressure into the valve and see what you get there. If everything is OK there then try checking the valve, and see what you get there. Let me know what you find. My email is open. If you want to hit me up that way I'd be more than happy to give you my number and help out any way I can. Wayne

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Kevin Wright

02-13-2014 16:18:15

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 Re: GEHL HL4400 BUCKET GOES DOWN BUT NOT UP in reply to NCWayne, 02-13-2014 14:00:08  
the high pressure line coming from the gear pump into the control valve is a big hose, too big for any fittings i would have access to to put on a gauge. what i dont understand is if the pump were going bad why do i have such strong pressure on the loader arm cylinders and the other end of the tilt cylinders. we took a hose off the end of the tilt cylinder and put it into a bucket and it shot over a quart of fluid out in just a twitch of the handle. its getting fluid but just very low pressure. im completely stumped....

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02-13-2014 17:23:20

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 Re: GEHL HL4400 BUCKET GOES DOWN BUT NOT UP in reply to Kevin Wright, 02-13-2014 16:18:15  
Ok, if you can't tap into the main line try hooking a gage into the line going to the other end of the tilt cylinders and the lines to both ends of the boom lift cylinders. In all cases take the cylinder to the end of it's stroke and see what kind of pressure you've got. This will give you a good idea what the system pressure is without having to tap into the main line. If it were me I'd check the pressure on the boom lines first since that function seems to be OK. That said, just the fact that fluid comes out of the line really doesn't mean anything as even a worn out pump will usually create flow, but not pressure. It all depends on the wear, but I've flow tested systems before and seen pumps act perfectly normal until the system pressure reached a certain pressure at which point both the pressure and flow dropped to near nothing. At that point you could remove the load/pressure and the flow came right back up, but as soon as a load was applied and pressure started to rise it was right back to nothing. Unfortunately the only way to really check things that way is with a flow meter with valve to load the system. That is the best way to check a hydraulic system given that pressure and flow are tied together like they are, but in a situation where nothing but a cylinder is involved, the flow doesn't mean as much as the pressure since the only effect flow has on the cylinder is the speed it works, and has nothing to do with the amount of force it can exert.

As far as why one function works and not the other, like I said before, the tilt back and boom down functions are both working off the rod end of the cylinders where the tilt forward and boom up are working off the tail end of the cylinder without the rod. Using round numbers think about it like this. With 100 psi on the rod end, the rod takes away surface area from the piston so there is only 1 sq inch of surface area for it to act on. With the one sq in, the force put out by the cylinder is only 100 lbs. On the other end, without the rod, the 100 psi is acting on the full surface of the piston which is, say 4 square inches of area. This gives the cylinder 400 lbs of force. Ultimately between the differences in the area of force the pressure has to act on, and the mechanical advantage achieved by the way the cylinder is attached, it's not uncommon to see one function seemingly act normal, while the others show a definite problem. This happens until enough weight is put on the system for the problem to show with every function. It's hard to say if that's an issue here without factoring in the weight of the loads you have been carrying, the length of the 'levers' involved, etc, etc and doing the math, but I have seen that make a difference and cause a problem to show at point A but not B and C until a situation occurred that pushed the 'stronger' functions past their limit. Hope that makes sense as I don't know any other way to explain it.

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Kevin Wright

02-13-2014 20:08:12

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 Re: GEHL HL4400 BUCKET GOES DOWN BUT NOT UP in reply to NCWayne, 02-13-2014 17:23:20  
I am in the process of locating a pressure test kit, i had borrowed one when i tested the first time, but i only could borrow the gauge and one fitting. every set of lines on this thing has a different type of fitting, new hoses, old hoses, couplings, close nipples, etc...its a nightmare! i need a gauge and an assortment of fitting so i can do tests on each line at the point it connects to the cylinder, and where it comes out of the control valve. ive talked to everyone i know locally about what the problem could be but they just scratch their head like ive been doing for the past month. you have been a big help, i really appreciate your patients. when i find some gauges ill do some more test and let you know what i find.

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02-14-2014 19:02:50

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 Re: GEHL HL4400 BUCKET GOES DOWN BUT NOT UP in reply to Kevin Wright, 02-13-2014 20:08:12  
Testing at just two locations will tell you a lot. Since the lines going to each lift and tilt cylinders are Tee'd together, all you need to do is put a gauge on the lines going to both ends of one of them either at the same time or seperately. With a gauge tee'd into one of the lines move the cylinder to the end of it's stroke and read the max pressure. Then put the gauge on the other end and take the cylinder to the other end of it's stroke and read that pressure. That will tell you whether the pressure the pump is making is the same on both circuits.

If the pressure is higher on the lift circuit than the tilt circuit, or different between the ends of the cylinder on the same circuit, that will help you pinpoint the problem. Now if its the same (low) on both ends of both cylinders then you could have either a bad pump or the main/system relief could be stuck open/damaged and dumping the pressure . Unfortunately the only way to test for that problem is to tap into the main line going into the valve and put a load on the system like I talked about before.

All you really need to do is put a load on the system and the actual flow rate isn't an issue, all you need is a Tee with a needle valve on the outlet/downstream side of the tee to give you the load capability. Slowly closing the valve should cause an increase in pressure. All you need to do is slowly close it and watch to see if the pressure reaches the spec. If it stops rising before you get there you know the pump is bad, if it continues to increase as you close the valve a little more then all is OK with the pump and it has to be the main relief valve.

If you want to get yourself an assortment of fittings and gauges to check this problem, and to have for future use, give Surplus Center a look. They are about the cheapest place I know of to get pretty much everything you might need to tap into and check the system.

Once you get everything checked out, like I said, shoot me an email, or post back and I'll be glad to offer up any assistance I can. Wayne

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Kevin Wright

02-13-2014 10:29:49

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 Re: GEHL HL4400 BUCKET GOES DOWN BUT NOT UP in reply to Kevin Wright, 02-13-2014 10:00:56  

here is some pics. i finally figured out how to get em on my computer.

the self-leveliing bypass valve and the housing it goes in, and the control valve as it sits in the machine.

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