john deere back hoe no down pressure

[xixxixxixxi]

I am stumped, my john deere back hoe suddenly lost almost all down pressure. Everything else works fine. I swapped the 2 hoses to the ram and the problem also flipped. I swapped the spool with another one and nothing changed. I swapped the pressure valve from top to bottom and one side to another and nothing changed. I connected both hoses of the problem ram to one of the other valves and it worked fine. One more thing I noticed, when i apply down pressure none of the other rams work but the down ram only works a tiny bit. Are there seals inside the valve assembly that can leak and this causing a loss of pressure?

 

[oldnslo]

What model of backhoe is this? Reason for asking is that on some models Deere used a pump that requires a feedback signal from the valve. From what you are describing it sounds like the feedback signal from the spool is being lost. Try running another function while operating the down function. If it works then that would indicate the feedback signal from that section is not getting to the pump. I am not sure the valve supplies this signal so cannot advise you on how to troubleshoot further.

 

[DMW]

Do the lines/valves have quick connects?

 

[xixxixxixxi]

What model of backhoe is this? Reason for asking is that on some models Deere used a pump that requires a feedback signal from the valve. From what you are describing it sounds like the feedback signal from the spool is being lost. Try running another function while operating the down function. If it works then that would indicate the feedback signal from that section is not getting to the pump. I am not sure the valve supplies this signal so cannot advise you on how to troubleshoot further.

the tractor is a 401C but the backhoe is not the original one that came with the tractor. It says john deere and has the number T67896 on the bucket. There are no electronics at all with this backhoe if that's how the feedback signal works. it runs off the same oil pump that supplies pressure to the loader (there is a manual valve I have to close to disconnect the loop to the backhoe if I want to use the loader). When i apply down pressure, nothing else works as if all the pressure is leaking away.

 

[xixxixxixxi]

no, none are quick connects

 

[oldnslo]

Xi
The feedback would be hydraulic and probably a small line like 1/4 or 3/8.

Without hydraulic schematic for tractor and hoe this is something I would look for.

1) is there a smaller hydraulic line connected to control on the pump. If yes then it requires a feedback signal from the valves

2) you stated that you swapped the pressure valves. Some of these valves seat on the casting. Did you check to make sure the cavity was clean when you swapped those valves. Do you here any noise like oil flowing when when the valve is operating? If yes that would point towards the work port relief bypassing.

3) depending on how the feedback signal is routed through the valve it might be possible something is stuck open and bleeding off all the feedback when you operate that one function .

I can稚 think of anything else that cause the problem you are experiencing

 

[xixxixxixxi]

Xi
The feedback would be hydraulic and probably a small line like 1/4 or 3/8.

Without hydraulic schematic for tractor and hoe this is something I would look for.

1) is there a smaller hydraulic line connected to control on the pump. If yes then it requires a feedback signal from the valves

2) you stated that you swapped the pressure valves. Some of these valves seat on the casting. Did you check to make sure the cavity was clean when you swapped those valves. Do you here any noise like oil flowing when when the valve is operating? If yes that would point towards the work port relief bypassing.

3) depending on how the feedback signal is routed through the valve it might be possible something is stuck open and bleeding off all the feedback when you operate that one function .

I can稚 think of anything else that cause the problem you are experiencing

there is no feedback line connecting the tractor to the backhoe. each valve has 2 lines going to its ram and there are only 2 large hoses coming to the valve assembly from the pump. other than that, there are no other hoses or wiring connecting the backhoe to the tractor.

when i swapped the valves, the cavity was filled with oil so i didn't notice anything. I can hear oil flowing somewhere by the valve assembly when i try to apply down pressure.

 

[oldnslo]

If you are hearing oil flowing then the problem is at the valve. There spool is all metal to metal seals so unless the casting broke no leak path there.

Work port reliefs could either seat & seal on the casting or have rubber seals on OD and metal to metal inside the valve. I would remove the relief valve then look to figure out potential leak paths.

If you have questions maybe post a couple pictures of the valves. Someone here might recognize them and provide you some ideas on what to examine

 

[Tx Jim]

T67896 is located in JD model 9250 backhoe parts catalog #1105. I'll suggest to check for a non seating relief valve. it would also be a good idea to check stand-by pressure which should be at least 2250 psi.

 

[Tx Jim]

T67896 is located in JD model 9250 backhoe parts catalog #1105. I'll suggest to check for a non seating relief valve. it would also be a good idea to check stand-by pressure which should be at least 2250 psi. I agree with xixxixxixxi in that JD closed-center hyd systems of that era have no small feedback line similar to the what CCLS hyd systems have.