Bobcat 641 with Backhoe problem

[CorDEX]

Hi, I have a bobcat 641 with backhoe attachment which has a problem when put into continuous flow. If I pull the aux lever to the left, the backhoe works fine, but when pushed right, past the detent into continuous flow, the backhoe doesn't work. The services that do move, do so only barely and then it is very very slow if at all if they are against gravity. I've tried swapping the backhoe hoses as the machine hydraulics seem right (male on top). Any help would be gratefully appreciated.

 

[Tazza]

Swapping the hoses at the couplers should have done the job.... You moving the lever to the left just means the oil would flow the opposite way, there is no reason that i can see why it wouldn't work after you changed the couplers at the machine.

 

[TriHonu]

Swapping the hoses at the couplers should have done the job.... You moving the lever to the left just means the oil would flow the opposite way, there is no reason that i can see why it wouldn't work after you changed the couplers at the machine.

Maybe the valve controlling continuous flow is not working properly. With the ends swapped, and the lever pushed to the right but not past the detent does it work?
To properly test it you need a Pressure/Flow Test Valve.
You can test pressure by attaching a 4000psi gauge to the coupler and pulsing the continuous flow for a moment. The excess flow will dump over the pressure relief valve back to tank. You can measure the pressure, however it will not tell you much about the volume of oil that is flowing. For proper operation you need X gallons/min at pressure Y.
Do you have any other attachments or a double acting cylinder to visually test it?

 

[CorDEX]

Maybe the valve controlling continuous flow is not working properly. With the ends swapped, and the lever pushed to the right but not past the detent does it work?
To properly test it you need a Pressure/Flow Test Valve.
You can test pressure by attaching a 4000psi gauge to the coupler and pulsing the continuous flow for a moment. The excess flow will dump over the pressure relief valve back to tank. You can measure the pressure, however it will not tell you much about the volume of oil that is flowing. For proper operation you need X gallons/min at pressure Y.
Do you have any other attachments or a double acting cylinder to visually test it?

Hi, Thanks so much for trying to help. I will try the machine without an attachment and report back as to whether the engine bogs. I have a snowplough/grader that's a two way attachment and it works fine, although it doesn't use continuos flow of course. The acter doesn't work at all when pushing the lever to the right, whether in continuous flow or not. The backhoe has had the spool valve replaced, but this was done by a hydraulics company and I assumed it was right, but have no way to check...

 

[CorDEX]

Swapping the hoses at the couplers should have done the job.... You moving the lever to the left just means the oil would flow the opposite way, there is no reason that i can see why it wouldn't work after you changed the couplers at the machine.

Okay, so more on this one! I changed the couplers at the machine rather than the attachment by way of a sanity check and now, when pushing the right hand stick towards the detent the backhoe works meaning I can use my other hand to operate the levers, great if you have three hands!. However.... When I push the lever further right, past the detent, the hydraulics stop, with only tiny movements on the backhoe towards gravity. There seems to be no pressure/flow (not sure which) when the Aux lever is pushed past the detent. Any ideas?

 

[TriHonu]

Okay, so more on this one! I changed the couplers at the machine rather than the attachment by way of a sanity check and now, when pushing the right hand stick towards the detent the backhoe works meaning I can use my other hand to operate the levers, great if you have three hands!. However.... When I push the lever further right, past the detent, the hydraulics stop, with only tiny movements on the backhoe towards gravity. There seems to be no pressure/flow (not sure which) when the Aux lever is pushed past the detent. Any ideas?

From your description I would start with the mechanicals.
Raise the cab and check the linkage. Make sure the valve spool is being moved and held in the open position when the handle is latched for constant flow. It may be as simple as corrosion on the spool from not being used.
If mechanically the linkage is operating the valve spool. Then the issue in the valve. You would need to pull the spool and inspect the seals and ports.
You can view exploded views of the valve at Bobcat Parts Online. Click the Model Number Tab, then search for 641. You will need the serial number of your loader to id the correct valve in your loader.

 

[CorDEX]

From your description I would start with the mechanicals.
Raise the cab and check the linkage. Make sure the valve spool is being moved and held in the open position when the handle is latched for constant flow. It may be as simple as corrosion on the spool from not being used.
If mechanically the linkage is operating the valve spool. Then the issue in the valve. You would need to pull the spool and inspect the seals and ports.
You can view exploded views of the valve at Bobcat Parts Online. Click the Model Number Tab, then search for 641. You will need the serial number of your loader to id the correct valve in your loader.

Again, thanks so much for helping. It's very much appreciated. I've done this and when moving the lever towards the detent the rod pushes into the spool valve. Moving past the detent actually seems to push the rod further into the valve, it doesn't just hold in place. I guess it points to the spool valve on the machine? But typically it's in a very awkward place. Almost looks like the engine needs to come out to get at it! I'm right in thinking that the backhoe doesn't need a high-flown machine, right?

 

[TriHonu]

Again, thanks so much for helping. It's very much appreciated. I've done this and when moving the lever towards the detent the rod pushes into the spool valve. Moving past the detent actually seems to push the rod further into the valve, it doesn't just hold in place. I guess it points to the spool valve on the machine? But typically it's in a very awkward place. Almost looks like the engine needs to come out to get at it! I'm right in thinking that the backhoe doesn't need a high-flown machine, right?

&nbsp
No you don't need high flow to operate a backhoe. In hydraulics, the volume of flow determines how fast a motor or cylinder moves. The pressure determines how much force you can produce.
Many of us when learning to operate a hoe ran the engine at part throttle to reduce the hydraulic flow. The hoe will move slower and is easier to control. As you skills improve, you will probably increase the throttle to have the hoe capable of moving quicker. I have operated a few hoes that had control valves that offered very little feathering. (i.e. barely move a lever and go from stop to full speed). If you are doing precise excavation, you may have to throttle down so you can control the cut.
I hope someone else will jump in here. I am not familiar with the manual controlled Aux. Based on your statement that the spool is moving as you lock into continuous flow, I'll take my best guess that either the valve spool is either not moving far enough (linkage out of adjustment) or you have a damaged seal.

 

[CorDEX]

&nbsp
No you don't need high flow to operate a backhoe. In hydraulics, the volume of flow determines how fast a motor or cylinder moves. The pressure determines how much force you can produce.
Many of us when learning to operate a hoe ran the engine at part throttle to reduce the hydraulic flow. The hoe will move slower and is easier to control. As you skills improve, you will probably increase the throttle to have the hoe capable of moving quicker. I have operated a few hoes that had control valves that offered very little feathering. (i.e. barely move a lever and go from stop to full speed). If you are doing precise excavation, you may have to throttle down so you can control the cut.
I hope someone else will jump in here. I am not familiar with the manual controlled Aux. Based on your statement that the spool is moving as you lock into continuous flow, I'll take my best guess that either the valve spool is either not moving far enough (linkage out of adjustment) or you have a damaged seal.

Thanks, I'll have a go at adjusting the linkage this weekend and report back. I hope the spool doesn't have to come out, it's in a very awkward place!