M7040 Boom hydraulics have low power.

[EyrieWatcher]

I have an M7040 with a M20 loader equipped with a Walvoil SDM 143-2 control valve (https://www.walvoil.com/allegati/catalogo/DAT009_ENG.pdf).

Presently there is very little hydraulic power on boom under normal operation and no lifting power at low rpm.
I need to have the engine over 2000rpm before I can lift a round bale and even then it moves very slowly.

The tractor does have full power on dump and also full power to the remotes at the back of the tractor through the power beyond port.
There are no external leaks of hydraulic fluid and I have replaced the hydraulic fluid and filter.

The interesting part is that if I engage the dump, curling the bucket back, wait for it to bottom out, and then while it is still engaged pull back on the boom, full lifting power returns to boom but only while dump is engaged.

This seems to rule out a stuck pressure relief valve and bad pump but I am a mechanical novice and hydraulics are not my specialty.

My thought is possibly a worn spool or control valve and that I am getting a leak back but I don't fully understand the hydraulic flow to confirm that.
The tractor has not seen heavy use an only has just over 1000 hours on it and is not abused.

I'm wondering if anybody else with more hydraulic understanding might be able to point me in a direction.

 

[North Idaho Wolfman]

Check the linkage to the spool valve.

 

[EyrieWatcher]

Thanks, I'll have a look there next.
I also just discovered that the issue is only raising the bucket.
If I put blocks under the bucket I can lift the front end of the tractor without any issue.

 

[Russell King]

You should check any and all quick couplers to be sure they are correctly connected together. You may be able to just remove the couplers and direct connect the hoses to see if that resolves the problem.

I think you could also swap the curl hoses with the boom hoses and see if the slow movement follows the hoses/valve spools or not.

I recall a lot of discussion on some issues with the regenerative dump function. (Don’t remember exactly what the issue was but you may be able to search on “regenerative dump” and find the issue). Only if your system has the regenerative dump capability!

 

[EyrieWatcher]

I was headed down that way Russell and one of the quick couplers seems to be stuck (probably rusted in place) so I have them all under oil now. Regenerative dump is something I've never heard of before though.

 

[EyrieWatcher]

Wolfman had it!
There was more slop in the boom than normal. I lifted up the positioner kit housing and checked that the spring was still good. I also opened the connection at the bottom to the spools.
After reassembling I now have full function!

Thank you folks.