You can bypass the cooler as you suggested, but my thinking is, if the hyd pump is putting out 14 gpm the oil has to be going somewhere since the hydrostats do not take that much flow since the hydrostats are a closed loop and the only oil going into them from the circuit is what is lost through the case drain. If the flow was being that restricted at the cooler I would also think the pressure would increase to a point where the cooler would explode. Having said that, the only way to know for sure is to either tee a pressure gauge into the circuit before the cooler or do as you suggest and bypass the cooler. It would be better yet if a gauge could be installed before the filter, but I don't believe there are any test ports.
L555 Please save me from divorce!
- Thread starter palmtree
- Start date
It will be tough to tee-in a pressure test port anywhere because everything is hard lines without much give. That's why changing the charge check valve was so difficult and time consuming. Is there something in the control valve that could dump oil into the chain case thus robbing volume and pressure from the charge circuit?
I have noticed what looks like it could be a test port on the top of each motor. Is that what it is? Would it do any good to test the pressure there?
Those are not test ports. The only place where you could possibly tee into the lines with a pressure gauge is at the tee right before the elbow which is attached to the charge check valve. You would need to remove it and drill and tap a hole into the tee so a gauge could be attached provided there is enough room for one. I think before you do that, remove the filter and check if the openings are fully open. Also remove the line from the tee at the check valve to that filter and make sure the line and the filter base is clear. If everything is clear then there should be no obstruction reducing the flow and the problem lies in the pumps or motors. If that is the case then you will need to plug the hoses at the motors and then check charge pressure and case drain from the pumps as I stated in an earlier post.
My plan for this weekend (probably Sunday) is to temporarily bypass the oil cooler hoping for a restriction and check the charge pressure. I figure that is a long shot but at least it should be easy to do. Then I will remove the hoses from the motors and plug them. Start it up and check the charge pressure. Then I will run another pump case drain flow test with the motors out of the loop. Depending on what I find there I may remove the filter and check the housing for obstruction. That ought to be plenty for a guy that works as slowly as I do. And it all depends on the weather too. I can't run the machine in the garage -- even with the door open since my garage is in the basement. I could reattach the exhaust extension that I used earlier but it's a pain. I'll report back with my results. Wish me luck.
Do the simple stuff first like Mike says and check that you have full flow through the filter and then the cooler then the rest of it. good luck
Thanks Jerry I will do as you say. Quick question. If there was a way to measure the flow through one of the hoses from the pump to the motor (say a flow meter that can handle high pressure and high flow). And measure the flow out the other side of the motor into the other side of the pump simutaneously and subtract the two -- wouldn't that give you the case drain per minute from the motor? Could you do the same thing with pressure? Wouldn't there be a pressure drop on the outgoing side if the motor is leaking significantly? Don't get me wrong. I don't have the tools necessary for making these measurements. I'm just trying to understand how they work.
Two flow meters would do as you say. Pressure would not tell you anything unless when you stalled the motors the pressure was less than the relief valves were set for. After the oil does it's work by rotating the motor shaft, the oil drops to @ charge pressure. It would be nice to install a flow meter on the hose going to the hydro pumps.
Weekend Update. The weather is really crappy today so I had to reinstall the exhaust extension so I could run the machine in the garage. I bypassed the oil cooler with a 3 foot hose and started it up. Same as usual. Charge pressure at 150 psi and slowly lowering as the oil heats up. I didn't run it for long but it didn't take long to see that the oil cooler is not the problem. Then I removed the hoses from the motors and plugged them. Ran it again and checked the charge pressure. Same as before -- charge pressure at 150 psi and slowly moving lower. When I stroked the levers the charge pressure stayed the same (maybe lowered 1 or 2 psi). Then I attached a hose to the pump drain case line and put the other end in a 5 gallon bucket. Started the machine and then started my stopwatch. Once again it took a while before I saw anything coming from the hose and when it did it as coming slowly. The flow did not noticeably increase when the levers were stroked several times. I ran the machine for 2 minutes and measured just under a half gallon (so less than a quart per minute for both pumps at once). If I understand correctly then I am safe to assume that the pumps and motors are not the problem. Good news for the guys who rebuilt them -- bad news for me beause I'm still clueless to what's causing the problems. I decided to remove the filter housing and inspect it for a restriction of some sort. I had to take several things apart to get it but when I finally did it looked good. Nothing I could find that looked different than expected. Honestly I wouldn't expect a restriction somewhere to be worse when the oil heated up -- I would expect the opposite thinking it would move through the stenosis easier when the oil is warm. Would I cause any problems if I ran a 1/2" hydraulic hose from the output side of the gear pump directly to the input of the oil cooler. That would bypass the control valve and all of the lines between the gear pump and the oil cooler. Of course I would lower the boom first so I could try to drive it like that. I'm not sure if there is some sort of solenoid that would not allow it to run without going through the control valve. Any ideas would be appreciated. thanks, Brett the Clueless
You could run a hose from the pump to the cooler. I think it is time to have someone with a flow meter to check what the flow from the hydraulic pump is and also how much flow is going to the hydrostat pumps. If the hydraulic pump is putting the gpm out the oil has to be going somewhere after it leaves the pump. Unless someone has done some creative plumbing there is only one place the oil to go since there is only one exit to the chain case and that is through the other filter. When you stroked the hydro levers it should have put a load on the engine to the point you could hear the relief valves opening which should have increased the case drain or if at a low rpm you should have killed the engine.
Maybe I didn't pull the levers hard enough. I pulled them and I could see the plugged hoses that normally go to the motors straighten out and the pumps would make some noise. The engine would bear down a little but it didn't seem like the engine was about to stall. I suppose I could pull the levers harder, they are really stiff with the hoses capped. Am I right to think that something clogging the line would get better as the oil warms up instead of worse? It seems to me that the problem must be in either the output of the gear pump or maybe there is some kind of diverter valve that is stuck open and as the oil warms up it flows through faster.
Oil will flow faster when hot, but will also leak more and bypass the pump gears easier. There are only three places where oil can re-enter the chain case. The return filter, hydro pump case drain and motor case drain. If takes more than 150 psi to raise the loader so I find it hard to think the hyd pump is bad and as fast as the loader operated in your video it evidently has flow above a couple of gpm.
Hey Mike. So is it worth my trouble to run a hose directly from the gear pump to the oil cooler? Where do you think the oil volume could be going? Brand new charge check valve installed (probably didn't need it since nothing changed when I replaced it). I'll try to get a hold of a flow meter. Thanks again, Brett
A flow meter will tell you more. Every gallon of oil pumped by the hydraulic pump must go through the cooler, there is no place else for it to go.
This is crazy. I took the boom off the support pins and lowered it all the way down. Then I ran a hose straight from the outlet of the gear pump to the inlet of the oil cooler. This bypassed the control valve. I started it up and the charge pressure was just under 150 psi. I pulled it out and drove around a little. The strange thing is that it is quite a bit better but still not right. Before it would hardly turn at all even in the gravel. Today it would turn pretty decent but only if I would stroke one lever at a time. If I would stroke the left lever and keep the right lever centered it would turn and just push the right wheels sideways (it didn't like to do that before). However, if I move the one lever forward and the other backward at the same time it wouldn't do that well (jumpy and the pumps would growl). After a few minutes of driving around the charge pressure was down to about 125 psi. Also I noticed that when I'd push both levers in opposite directions simultaneously the charge pressure would drop to well below 100 psi (maybe 80 or 85 psi). I still think it must be the gear pump. I think it's pushing oil, just not enough volume quickly enough to supply the need when under a load. It just had a little less resistance with the line straight to the oil cooler. Does that sound reasonable?
There is no doubt you had less restriction on the hyd pump by going around the control valve. You might as well take the hyd pump off and disassemble it. I am sure it could use a seal kit anyway. Check the bores where the gear shafts rotate for a lot of wear. If the seals under the gears go bad they do not put enough pressure against the gears to pump oil at full volume. If the shafts are still snug in the bores then reseal the pump. If they are loose then replace the pump. Mark each section of the pump before you disassemble it because you can get the center section in the wrong orientation. I make a "V" scratch across all three sections so everything goes back as it was.
I'm thinking about just buying a new gear pump. The seal kit for mine is $89 and I can buy a new pump for $208. My question is whether or not I can/should buy a new pump that moves a higher volume of oil? The newer version of mine (26007-RZE) is rated at 15 GPM. There are larger displacement versions with the same flange and shaft that move more oil per minute. Is there a benefit to using a higher flow model (maybe for aux hydraulics)? Is there a reason not too? It's not much more money. thanks again, Brett
Two issues. To gain gpm the center section of the pump is wider, this will relocate the fittings slightly. This may or may not be an issue. The more important issue is the system may not be designed for higher oil flow, especially the charge check valve. This will cause oil overheating and build backpressure which could affect your boom and bucket circuits.
Thanks Mike. I couldn't come up with a good enough reason to gamble on a new pump with higher displacement. I know I don't want to buy a new oil cooler next. However, I do think the charge check valve is up to the task since according to Partspring it is the same valve used for lots of NH skid steers -- even up to the LS-190B which I know has higher flow than my L555. I'm sticking with the 26007-RZE which as best I can tell is the replacement for my 26007-RAA. Thanks again for your help and I'll report back when it comes and I get it installed. I'm excited because I know it is only about a 10 minute job. I think it's probably the easiest thing you can do on this machine.
The new gear pump arrived today. I promptly removed the old pump and installed the new pump. Exchange was simple and quick. Then I removed the line bypassing the control valve and reinstalled the hose from the gear pump outlet to the control valve. Started it up and the charge pressure was at 150 psi. Backed it out of the garage and drove around a little. The dang thing is operating just like before the new pump($225), which is just like before the new charge check valve($110), which is just like before the rebuilt hydrostatic pumps($1600), which is just like before the rebuilt drive motors ($1300). I'm running out of parts to replace on this thing. I'm really at my wit's end. Please help me figure this out. I'm obviously too far in ($$$$$) to give up now. Thanks again, Brett
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