I bought a 2015 Case 580SN Backhoe recently. It has the pilot controls for the backhoe. I had mainly used it for front end loader work till recently. I was using the backhoe yesterday to dig a trench and I noticed when I was digging if I pulled the dipper into the face of the excavation the hydraulic pressure would start to pull hard but then immediately cut out. If I started to curl the bucket then both the dipper and bucket had full hydraulic pressure. When I moved the dipper away from the backhoe and pushed against the back of the cut it has full hydraulic pressure and doesn't cut out. The next thing I noticed was when I tried to move the machine forward I was lifting the back end with the boom and pushing the machine with the dipper but I wasn't able to push the machine - the hydraulics would start to push and then cut out. When I was doing this I had the front bucket flat on the ground and lifting the front wheels slightly. With my previous machine I would be able to push with the dipper and move the machine forward with the bucket sliding on the ground. I lifted the bucket off the ground and then I was able to move the machine forward with no problem. I then did some testing - with the front bucket off the ground I had full hydraulic force on the dipper pulling in and pushing out against the trench. As soon as I dropped the front bucket on the ground and lifted the front end slightly I no longer had full hydraulic force pulling the dipper in towards the backhoe unless I activated the bucket curl at the same time. There seems to be something happening in the hydraulics that when the front end loader is pushing down to lift the front end it causes the dipper hydraulics to cut out with very little force being applied. It doesn't seem to effect digging with the backhoe very much because when digging I am normally crowding the cut face with the dipper at the same time as curling the bucket to load it. As long as both functions are acting at the time the dipper hydraulics seem normal. I'm confused how what the front end loader hydraulics are doing can cause the backhoe dipper hydraulics to operate differently but I am new to pilot controls and maybe there is some simple explanation for why this is happening. I would feedback from anyone who has any suggestions about what is going on.
I made a mistake in one of the descriptions of the problem in the original post. Just to clarify the dipper hydraulics work normally with full force both towards and away from the backhoe if there is no down pressure on the front end loader bucket. When the front bucket is lowered to lift the front wheels the dipper hydraulics will cut out when pulling the dipper in towards the backhoe as soon as the bucket touches the ground. You can hear the engine start to load up for a second then it immediately drops off and the dipper stops moving. When moving the dipper out away from the backhoe the hydraulic operation is normal. I have looked through the service manual but cant see anything that would explain how the front end loader hydraulic position could effect only one of the backhoe functions.
Is there a sensor on the boom for load level or return to dig that could be causing this?
The front end loader has return to dig but nothing on the boom that I know of. I do notice on this machine (580SN) that when a cylinder gets to the end of its stroke the engine rpm initially drops as the hydraulic pressure builds and then then it feels like the pressure drops and the rpm returns to normal. On my previous Super M machine with manual controls the engine rpm would drop at the end of a cylinder stroke as well but I am pretty sure it stayed at the lower rom as long as the control lever was held open. I just found the statement below in the service manual. This may explain why the engine rpm drops at when a cylinder is heavily loaded or at end of stroke and then the pressure seems to drop and rpm recovers. This could explain why the dipper hydraulic pressure seems to cut out but still not sure why it cuts out in the one direction with very little load when the front end loader has down pressure. "All Super N machines are equipped with a torque regulation feature to control engine loading from the hydraulic systems."
Complete stab in the dark, but shut off ride control and see if that changes anything.
Ride control is normally off because you cant have down pressure on the front bucket when ride control is on. I have tried turning it on when the bucket was down and the front wheels raised off the ground and it lets the front end drop to the ground and than feel of the controls is the same as lifting the bucket with ride control off
After playing with the machine for another day and doing some more test digging as well as reading up on the difference between my previous 580SM and now the 580SN I think I probably don't have a problem. Its just a matter of getting used to the new machine. Here's a long winded explanation. From what I have read online the 580SM was a constant volume gear pump and open center hydraulic system. When a control lever on the backhoe was pulled and the cylinder couldn't move because the ground was too hard the main pressure relief valve would relieve but there would still be full hydraulic pressure on the cylinder. The 580SN is a variable displacement axial piston pump. Here is a description from a Case data sheet. "Pilot Backhoe Control Valve Six, seven, or eight spool sectional closed center control valve. Features “Pro-Control” which includes custom designed spools for each individual function along with “swing cushioning” valve for zero-wag swing control. Basic control valve is closed center, with circuits in parallel with a post-compensated, flow sharing feature for simultaneous operation of all circuits." From what I read on other sites when the flow to a cylinder stops like when the dipper is moving towards the backhoe but cant move anymore when it is tight against the ground, the pump output will drop to a much lower flow. That is likely what I am feeling when I say the hydraulics cutout and the rpm increases. There were two things I thought were a problem. 1. With the front bucket down and the wheels off the ground and the dipper pulled against the ground as it moved towards the backhoe at some point the hydraulics would feel like they "cutout". It now makes sense that this is the feel when the variable speed pump goes to low output. When I lifted the front bucket so the front wheels are on the ground I was able to move the backhoe when the dipper pulled against the ground. I originally thought that was happening because the hydraulics were working differently and had more force but now I think it is just the related to the weight shift. With the front bucket off the ground it is not resisting movement and there is less weight on the rear stabilizers. As a result the lower resistance and weight shift allows the dipper to be able to move the backhoe without the pump dropping to low output. 2. I was concerned that the dipper hydraulics seemed to "cutout" when the dipper was against the ground in the cut but if I started to curl the bucket, the dipper seemed to get full force again and not "cutout". I think all that is happening is when the dipper stalls against the cut the pump goes to low flow and when the bucket curl control is started the pump goes back to full flow so both the bucket and dipper get full pressure and flow. Also as the bucket curls it is loosening the ground ahead of the dipper so that allows the dipper to pull through the ground more easily. Hopefully I'm right and its just a learning curve with a new machine. All my other backhoes prior to this were the 4 stick with foot pedal swing. I still need quite a few more hours to get comfortable with the pilot control joysticks so that combined with a different design hydraulic system made me see problems where there hopefully aren't any. Stay tuned.
I think I would be checking pressure on the cylinder when the symptom occurs. I would want to know if there is a circuit relief valve out of adjustment or failing. I have operated a lot of different back hoes and when you ddead end or get against an unyielding load the pressure relief valve let’s loose. They make a noise unlike any other. I’m certainly not disputing what you have figured out, but I always say,don’t search until you find an answer that you wanna hear. Instead, search for an answer that actually addresses the problem specifically
I’m with Tink, something doesn’t sound right. Why would the pump go to low pressure when it needs it most.
Re comments from Tinkerer and Harley Happy - This is the ninth backhoe I have owned as well as half a dozen farm tractors. I am used to the sound a relief makes when it lets go when a cylinder bottoms out or is against an unyielding load. Aslo the significant drop in engine rpm that only recovers when you let go of the control lever. All of my previous equipment was open center hydraulics with fixed displacement pumps and they all felt and sounded similar in this situation This is the first machine I have had with closed center hydraulics and variable displacement pump. I shouldn't have said the pressure cuts out in one of my posts - the pump goes to minimum displacement when the relief pops so that change in flow is what makes it feel like the hydraulics cutout and the rpm also recovers because it takes less horsepower to push a much lower flow through the relief valve. When digging I first noticed the difference with the dipper when pulling into the cut and the hydraulics feeling like they "cutout". When digging the dipper pulling in is the most likely function where the movement will be stopped due to unyielding ground. The bucket has a lot more breakout force when curling in so it very seldom stalls and pops the relief. If you push down on the boom it just lifts the back of the machine so doesn't pop relief. You are normally raising the boom after the bucket is full at the same time you are moving the dipper away from the machine to get ready to swing and dump the bucket so no popping the relief. Because it was primarily happening when pulling the dipper into the cut it made me think it was a problem with only the dipper hydraulic function. Now that I understand better the closed center hydraulic operation with variable displacement pump I spent some time playing the backhoe this morning. I ran the boom, bucket and dipper through the cylinder full stroke for them all in both directions. At the end of the stroke the relief valve pops and the rpm drops for a fraction of a second. Then the you feel a pulse in the machine, the relief valve noise gets a lot less and the engine rpm recovers as the hydraulic pump goes to minimum flow. It is still relieving so the pressure hasn't dropped, just the flow. All of the functions act and sound the same at both ends of the cylinder stroke - it has the same feel that I originally thought was the hydraulics cutout but I am pretty sure that is just the variable displacement pump doing its thing. Before I spend time to do hydraulic pressure and flow testing, I plan to find someone with a 580SN in my area and see if I can play with it for a few minutes. If everything sounds and feels the same as mine there should be nothing to worry about - it will be just getting used to the new machine, If not I will know I have to investigate further.