Loader Hydraulic valve problem

[ozarkbru]

On my B7800's loader the bucket will float down but not power down.
Last weekend while using my backhoe I was lifting the front end a lot over a few hours, after that I did some some loading and back dragging then trouble started, it would not lower with pressure. The valve was hot, Both white and yellow lines appear to flex under pressure but all other positions work well.
, check valve?

 

[KWentling]

If it will go down when in the float position that about eliminates anything like an unseated QD or mechanical binding. Are the yellow and white lines the raise and lower lines or pressure/return lines supplying the valve ( or some other combination)? I don't know for sure but I would think load check valves would have to be OK for the float to work. You get no down movement at all under pressure? Does the valve go over the pressure relief when held in the down position? Pretty much has me stumped at this point. Maybe a nut has come off one of the cylinder rods and the piston is free? You might try pulling hoses off the cylinders and sticking them in a bucket and check for flow. Make sure the loader is down or supported before taking any lines loose.

Kim

 

[CHDinCT]

Not familiar with the B7800 but a common trouble shooting step is to reverse the lines from bucket curl/dump and boom raise/lower to see if the problem moves with the line change. If it does, the issue is likely in the valve, but if not, the restriction is likely in the raise/lower circuit somewhere. Also, a lot of these issues are solved by removing and reinstalling the quick connects. Sometimes they seem seated, but are not fully, which could cause the symptoms you had before it went fully dead.

 

[ozarkbru]

Both replies gave good ideas to try, thanks I'll be sure to let you know the results.
Bruce.

 

[tr11439]

Another common problem is that people tend to use Teflon tape to seal the threads. Teflon will break down and cause restrictions within the system. Make sure that you use a liquid sealer. Loc-Tite makes a good one.

 

[oldnslo]

+1 on the QD"s not being seated or worn slightly. Floating down there is limited flow and pressure.

Powering down gives higher velocities which can cause the check's in the QD"s to seal and if it is the return line both hoses would stiffen from pressure.

Roy

 

[ozarkbru]

Thanks for the replies,
Just got done swapping hoses and watching what was going on, when pushing forward both lines off of the white and yellow ports (bucket up and down) are under pressure, where the white line should be exhausting, it is not.
Does any one have a schematic of this valve? I'll probity have to go to Kubota for the parts any way.
Bruce.
The speck book for the LA402 doesn't include port info.

 

[oldnslo]

If are looking for a parts break down for the quick disconnects (QD) I don't think you will find one. About the only item replaceable on them is the O-rings. If the QD is bad replace it. You just have to figure our which half is at fault.

Does your QD have ball or poppet style seats in them. If poppet style look at the poppets to see if one of them appears wore down so it protrudes less than the others.

If the QD's are not original some one may have put on a ball style nipple with a poppet style coupling. This will work for awhile but will eventually cause the problem you are describing.

Roy

 

[7800DUDE]

make sure your 3 pt hitch lever is not engaged so times that happens

 

[ozarkbru]

make sure your 3 pt hitch lever is not engaged so times that happens

That's interesting, Too late to check it out but I know the problem has nothing to do with the QD's.