Bobcat 313 - hydraulic problem

[Handyfixer]

Dear readers, I recently bought a Bobcat type 313 and have the problem that the 4 hydraulic cylinders are shocking when lifting. Lifting weight is not a problem. The downwards movement is going very smooth. Does someone recognize this behaviour? I belief it could only be the pump, oil filter or air into the oil suction line but before I start de disassemble everything, I was hoping to find here someone with experience. Regards from Belgium!

 

[Tazza]

How long has it been doing this? is it noisy when you operate the hydraulics?
It does sound like air, if you haven't opened the system for a while and it hasn't gotten better on it's own, it could be a leak allowing air into the system, worn pump causing cavetation (air bubbles) or a filter restriction which will also cause cavetation.

 

[Handyfixer]

How long has it been doing this? is it noisy when you operate the hydraulics?
It does sound like air, if you haven't opened the system for a while and it hasn't gotten better on it's own, it could be a leak allowing air into the system, worn pump causing cavetation (air bubbles) or a filter restriction which will also cause cavetation.

Hi Tazza, Thanks for the reply. The only strange sound I'm hearing is when I'm lifting the bucket completely upward and the lifting cylinders are completely at the end of their stroke. When I keep on pushing onto the pedal the pump is making a strange noise. Personally I have the impression that the flow of the pump is not high enough, which results in the fact that the cylinder stops until sufficient oil has been pumped and the cylinder starts to move again. Air in the suction line would also be possible but I don't see a leakage nor crack in the suction hose of the oil pump and the oil level is OK... Strange though is that the pump must built up pressure as lifting weight is not a problem. The previous owner was telling me that the filter was recently replaced. As I don't have technical information about the filter element, I would not be surprised this filter might be the correct one and is restricting the oil to pass fast enough... Hope this explanation will enable you to provide some new idea's. Best regards,

 

[Tazza]

Hi Tazza, Thanks for the reply. The only strange sound I'm hearing is when I'm lifting the bucket completely upward and the lifting cylinders are completely at the end of their stroke. When I keep on pushing onto the pedal the pump is making a strange noise. Personally I have the impression that the flow of the pump is not high enough, which results in the fact that the cylinder stops until sufficient oil has been pumped and the cylinder starts to move again. Air in the suction line would also be possible but I don't see a leakage nor crack in the suction hose of the oil pump and the oil level is OK... Strange though is that the pump must built up pressure as lifting weight is not a problem. The previous owner was telling me that the filter was recently replaced. As I don't have technical information about the filter element, I would not be surprised this filter might be the correct one and is restricting the oil to pass fast enough... Hope this explanation will enable you to provide some new idea's. Best regards,

Ok, the noise at ehe end of stroke, is it like a whistle? that will the the relief valve opening.
To know for sure, you need to get the pump flow tested. They load the pump down, and check the flow to see if it's still within spec. When they wear, the flow drops and it takes more rotations to get up to pressure, making things go a lot slower.

 

[Hotrod1830]

Ok, the noise at ehe end of stroke, is it like a whistle? that will the the relief valve opening.
To know for sure, you need to get the pump flow tested. They load the pump down, and check the flow to see if it's still within spec. When they wear, the flow drops and it takes more rotations to get up to pressure, making things go a lot slower.

It sounds exactly like air in the lines. The cylinders will act real "jerky" through their travel. More so on the extend than retract. It is often accompanied by a strange sound when the air gets back to the pump. Simular to a vehicle low on power steering fluid. Is this what you are describing? If yes, continue reading. I am going to assume you just bought this machine? Has it been doing this the entire time, or did it just start doing it? The obvious question is how is the fluid level? You said you checked it, but lets make sure. The fluid level is checked on the side of the chain case with plugs. You should remove the UPPER plug and have fluid run out. If not, fill it unit oil runs out the upper plug.
Next is prior service. Does it have any new hoses installed? If yes, sometimes air will get trapped in the system and will take some time to escape by itself. Sometimes longer than most new owners will wait. You can bleed the system to speed up that process if that's the case.
Next is the pump sucking air. Make sure the suction hose is in good shape. No cracks or weathering. Just because they don't leak, doesnt mean they are sound. Also make sure all the clamps and the filter are tight. I have had ALOT of cases of loose hose clamps on the suction hose cause air in the system.

 

[Handyfixer]

It sounds exactly like air in the lines. The cylinders will act real "jerky" through their travel. More so on the extend than retract. It is often accompanied by a strange sound when the air gets back to the pump. Simular to a vehicle low on power steering fluid. Is this what you are describing? If yes, continue reading. I am going to assume you just bought this machine? Has it been doing this the entire time, or did it just start doing it? The obvious question is how is the fluid level? You said you checked it, but lets make sure. The fluid level is checked on the side of the chain case with plugs. You should remove the UPPER plug and have fluid run out. If not, fill it unit oil runs out the upper plug.
Next is prior service. Does it have any new hoses installed? If yes, sometimes air will get trapped in the system and will take some time to escape by itself. Sometimes longer than most new owners will wait. You can bleed the system to speed up that process if that's the case.
Next is the pump sucking air. Make sure the suction hose is in good shape. No cracks or weathering. Just because they don't leak, doesnt mean they are sound. Also make sure all the clamps and the filter are tight. I have had ALOT of cases of loose hose clamps on the suction hose cause air in the system.

Hi guys, Thanks for all the replies and ideas. Meanwhile I've found the problem. I disconnected the pump and found out that it still was pumping oil and shaft was rotation smoothly. Then I took off the complete oil filter and when I blew into the entrance I noticed a lot of resistance, so dirt inside... bought a new one and the problem was solved. As the previous owner so connected the inlet hose to the outlet of the filter and the outlet hose to the inlet, the overpressure valve was not opening when the oil filter doesn't allow the oil to get through... so I also corrected this one. Now it's working perfect! Thanks again for your idea's!