640 loader issue

[hozjob]

I have a JD 6410 with a 640 loader and have lost power on the raise/lower function. It will raise slowly if empty, but won't lift anything. The curl function works fine, I can raise the tractor off the ground with the bucket. I thought I may have a bad boom cylinder so I rebuilt both of them. I also replaced all the hoses as they were showing their age. All the quick connect couplers were checked and are working properly. Which led me to investigate the tractor side for a cause. The raise/lower cable was damaged in an attempt to adjust it, so it was replaced. Is there something in the spool valve that could cause me to have a weak raise/lower function? It was being used prior to this to move some large rocks and trees without any issues, and then I was suddenly unable to lift a bucket of manure. Any help is appreciated.

 

[beenthere]

Find or make up a pressure gauge that you can connect to the quick connect couplers and see what pressures you are getting. Might tell the problem and help locate.

 

[rScotty]

Darn, I knew I should have paid more attention to Closed Circuit hydraulic systems... If there is power elsewhere then it sure sounds like the loader valve, but the problem I have is those closed system valves sometimes have recirculation (regeneration) built into the valve and I don't know just how yours is set up.

How about something simple: Can you depressurize the system and then swap the curl and boom lines on the loader control valve? If so, it would tell you something if the problem follows.

Someone tell me how hard is it to swap those on a closed hydraulic system or even possible? Tx Jim, am I all wrong? I'm guessing here. ....
rScotty

 

[Farmer495]

I'd swap the hoses first to rule out the loader, easy to do if you have 4 hoses, hard to do if a monoblock connector.

 

[hozjob]

I swapped out the bucket and boom circuits and I'm still not able to lift the tractor using the loader. So... that brings me back to the loader itself, which on one hand is easier because it's more straight forward, however I'll have to reopen both cylinders and check the seals.
I re-sealed one side and tested it. It will slowly lift the tractor.... and I mean slowly. I left the tractor sit with the front wheels off the ground for an hour or so and came back to find them resting on the ground. I'll open the other cylinder tomorrow and re-seal it as well. Do I need to bleed air out of the system? Or will that happen on its own with initial use.

 

[Farmer495]

I swapped out the bucket and boom circuits and I'm still not able to lift the tractor using the loader. So... that brings me back to the loader itself, which on one hand is easier because it's more straight forward, however I'll have to reopen both cylinders and check the seals.
I re-sealed one side and tested it. It will slowly lift the tractor.... and I mean slowly. I left the tractor sit with the front wheels off the ground for an hour or so and came back to find them resting on the ground. I'll open the other cylinder tomorrow and re-seal it as well. Do I need to bleed air out of the system? Or will that happen on its own with initial use.

Sounds like some progress. Air should purge by cycling loader several times.

 

[rScotty]

You may have to make up a simple pressure gauge on a Tee that can be moved to various places in the system. From your test, It doesn't sound like it is in the cylinder, hopefully in the valve.

As for air, it will usually purge itself as you use the loader. There will always be some, but whether you are compressing air or fluid can't be told from the pressure gauge and both give the same lifting force anyway.

rScotty