L-555 Hydraulic Charge Problem

[tucquan]

I have an L-555 loader with 3100 hrs on it. It had 2900 hrs. when I bought it from a dealer. A short time later the hydraulic charge light would come on and stay on for a few seconds. As time passed and I used the loader more I began to notice the hydraulic charge light would come on after I had driven some distance, maybe a hundred feet or more. The boom and bucket would not work, the machine would not move, and if I tried to move it, it would make a loud racket which I assume are the drive pumps. It was very noticeable when I moved a pile of stones several hundred feet. I had to go down a 200 foot driveway and turn right. Just about every time I turned, the light came on and all of the hydraulics went dead. I got around this by coming to a stop before I turned and the light did not come on. When I'm moving stone or dirt around a few feet and cycling the boom and bucket frequently, the light may come on for an instant and go out. There is no loss of hydraulics. Sometimes the light will stay on for at least a minute or more, and several times I shut it down and let it sit for a few minutes before restarting. The light will come momentarily and then go out. If I sit and let the motor run and don't touch anything, there is no unusual noises. I also noticed if I have the bucket tilted back and hit the pedal to lower the bucket, the light usually goes out. The loader runs fine and the bucket and boom work correctly when the light is out. I can run for a long time either plowing snow or moving dirt without any problem, and the next time I use it and travel a long distance, the light comes on. I talked to the dealer and he thought it might be the gear pump since all of the hydraulics stop working when the light comes on. My thought is if it is the pump, why doesn't it happen all the time? The fluid is up to the full mark on the dipstick, the screen is clean and the fluid looks clear although I don't know how old it is. Both of the filters have been changed. I have the operator and service manual. I looked at the troubleshooting section and I think I can rule out most of the repairs. The ones I can't verify according to the manual are a dirty relief valve, internal leakage in the control valve, or a malfunction of the charge pressure relief. I apologize for a long winded question. I wanted to list what I have observed since the problem started in the hope that if someone else has had the same problem, they will know what the answer is. I searched the forum and did not find anyone who has a problem similar to mine. Maybe I missed it. Any advice or suggestions are very much appreciated. Thanks, Bill

 

[Mike10]

Since the boom and bucket stop working, the only common part between the hydraulics and the hydrostats is the hydraulic pump. So you can eliminate anything in the hydrostat circuit. On early model 555s the oil pickup point was right behind the large gear in the chain case. It was possible that the rotation of the gear would interfer with the oil flow. On later models an angled extension was added to the cross tube so oil could be picked up away from the gear. That was just a momentary problem. For the light to remain on for a minute, the hyd pump is not picking up prime. A good start would be to remove the hydraulic pump and reseal it or if it is worn then replace it. I do not think it is the relief valve in the control valve since that oil still goes back to the charge check valve. Even with the relief valve open the oil is flowing from the pump. The oil has to go somewhere and oil the oil that enters the control valve flows out the same port whether from the cylinders or from an open relief valve. This oil then goes to the charge check valve where the oil has to reach a certain pressure before it can flow back to the chaincase, so if the pump is working there should be charge pressure and the light should be out.

 

[Mike10]

Since the boom and bucket stop working, the only common part between the hydraulics and the hydrostats is the hydraulic pump. So you can eliminate anything in the hydrostat circuit. On early model 555s the oil pickup point was right behind the large gear in the chain case. It was possible that the rotation of the gear would interfer with the oil flow. On later models an angled extension was added to the cross tube so oil could be picked up away from the gear. That was just a momentary problem. For the light to remain on for a minute, the hyd pump is not picking up prime. A good start would be to remove the hydraulic pump and reseal it or if it is worn then replace it. I do not think it is the relief valve in the control valve since that oil still goes back to the charge check valve. Even with the relief valve open the oil is flowing from the pump. The oil has to go somewhere and oil the oil that enters the control valve flows out the same port whether from the cylinders or from an open relief valve. This oil then goes to the charge check valve where the oil has to reach a certain pressure before it can flow back to the chaincase, so if the pump is working there should be charge pressure and the light should be out.

One of the suggestions from NH on early 555s was to overfill the chaincase. I am thinking like an additional 2 gallons.

 

[tucquan]

One of the suggestions from NH on early 555s was to overfill the chaincase. I am thinking like an additional 2 gallons.

Mike, Thanks for the response. I was leaning towards a problem with the gear pump losing its prime, but I don't understand why the light stays on so long if it is a momentary problem. I would think once the oil "settles down" the pump would regain its prime. The part about the pickup positioned too close to the gear on earlier models is very interesting. The serial number on mine is 589213. According to the owner's manual I have, the unit was built in 1982. One thing I failed to mention in my original post was I looked at the rubber hose that goes from the screen to the inlet of the gear pump. I thought the hose clamps may have been loose and allowing air to be drawn in. They are tight, but the rubber hose is hard as a rock. Maybe it has some cracks in it. I will have to cut it off. Is that a special hose since it is a suction hose? Thanks, Bill

 

[Mike10]

Mike, Thanks for the response. I was leaning towards a problem with the gear pump losing its prime, but I don't understand why the light stays on so long if it is a momentary problem. I would think once the oil "settles down" the pump would regain its prime. The part about the pickup positioned too close to the gear on earlier models is very interesting. The serial number on mine is 589213. According to the owner's manual I have, the unit was built in 1982. One thing I failed to mention in my original post was I looked at the rubber hose that goes from the screen to the inlet of the gear pump. I thought the hose clamps may have been loose and allowing air to be drawn in. They are tight, but the rubber hose is hard as a rock. Maybe it has some cracks in it. I will have to cut it off. Is that a special hose since it is a suction hose? Thanks, Bill

Your machine is an early model. I would go to your New Holland dealer for the hose before cutting it off. If you use some other hose, be sure it is for use with oil. There are seals inside the gear pump which push against a plate on one side of the gears. These seals get flat over time and the plate is no longer held tight to the gears which casuse a lack of suction and loose the pumps prime. The additional oil in the chaincase, I believe, was to cover more of the gear to cut down on the aeration of the oil.

 

[tucquan]

Your machine is an early model. I would go to your New Holland dealer for the hose before cutting it off. If you use some other hose, be sure it is for use with oil. There are seals inside the gear pump which push against a plate on one side of the gears. These seals get flat over time and the plate is no longer held tight to the gears which casuse a lack of suction and loose the pumps prime. The additional oil in the chaincase, I believe, was to cover more of the gear to cut down on the aeration of the oil.

Mike, I ordered a replacement hose and the seal kit for the pump. Your advice makes sense to me. I was hoping the problem would be somewhat easy to fix. I wanted to hear from someone who knows a lot more about skidloaders than I do. Thanks, Bill