Front blade hydraulic control issue

[Makeer]

Down pressure only in both positions of control lever. It's a front blade on a 1980 B7100D. The blade was on the tractor when sold new to a local funeral home and matches the tractor in color. You can faintly see a Kubota logo on the back side of the blade. It has one cylinder for up and down and two cylinders for left and right angling.

I have to lift the blade all the way up to get it up and down the ramp on my trailer so I know it was working properly when I unloaded it 4 days ago. Started it up this evening and the control lever that raises and lowers the blade pushes the blade down with both positions of the lever. Push the lever forward, blade goes down. Pull the lever back, the blade still pushes down. Plenty of pressure in both positions to raise front end of the tractor.

I disconnected and reconnected the hoses to the cylinder at the quick connects with no change to the above description. The right and left angle lever still operates correctly.

Any ideas?

Thank you

 

[jbeenemd]

I have an old L185DT with a front blade. The previous owner was a friend of my father-in-law and he purchased it from his estate after he passed away. I believe the blade is a Kubota original as well. I also had it do the same thing you mentioned. Did it on several occasions. I just let it sit for a while and a few days later when I went back to work on it the dang thing would work. My thoughts at the time was that something in the valve was stuck open. Maybe a bad return valve? The tractor is in fairly rough shape and the front control valve was worn out and dripped fluid. The handles were held on with baling wire!! The leak was so bad that I had to replace the control valve and have not had this behavior with the new control valve. With 30+ year old tractors, you can get some strange behavior at times.
Jackie

 

[Big Kahuna]

Makeer, sounds like you have a o-ring leaking on the spool valve that operates the blades up and down.

Big Kahuna

 

[Makeer]

Makeer, sounds like you have a o-ring leaking on the spool valve that operates the blades up and down.

Big Kahuna

Took hoses off valve body, took valve body off tractor and took valve body apart. All looked fine to me but what do I know. Took it to Kubota dealer and mechanic there confirmed. He said everything looked fine. They suggested it may be the cylinder. Can anyone direct me to something to read an how to service that cylinder?

Thank you for the replies.

 

[bobkeyes]

Here's what I would do.

First, retract the cylinder and unhook both lines from the cylinder. Remove QD's. Start tractor. There should be no oil from either line except a little drainage.
Move lever quickly in one direction. Oil should come from only one line.
Move the lever quickly in the opposite direction. Oil should come from the other line only, again except for some drainage. If this test is OK then the valve is probably OK. If you have oil coming from both lines in either position then the valve is at fault.

Next, hook up the line on the rod end of the cylinder only and plug the blind end. Now push the lever to try and RETRACT the cylinder. Hold it there. If the cylinder moves forward or extends any appreciable amount the packing in the cylinder is bad.

It will move forward because the oil is by passing the packing creating pressure on the blind end of the piston. Since the blind end has more surface area, because the rod takes up part of the area on the rod end, the piston will move forward even though you are trying to make it move rearward.

Hope this helps some.

 

[Big Kahuna]

Now think what's going on........worked fine 4 days ago..........now has pressure down in either positions on control valve...........the "wall" between up and down is broken.........you have a open hydraulic sytem which means pressure is flowing at all times..........now when you try and divert the pressure you get what?......control only one way......right?.........then something is not there to prevent this.........o-ring in the casting is leaking.
What control valve is this? Cessna or Parker?

Big Kahuna

 

[Makeer]

Here's what I would do.

First, retract the cylinder and unhook both lines from the cylinder. Remove QD's. Start tractor. There should be no oil from either line except a little drainage.
Move lever quickly in one direction. Oil should come from only one line.
Move the lever quickly in the opposite direction. Oil should come from the other line only, again except for some drainage. If this test is OK then the valve is probably OK. If you have oil coming from both lines in either position then the valve is at fault.

Next, hook up the line on the rod end of the cylinder only and plug the blind end. Now push the lever to try and RETRACT the cylinder. Hold it there. If the cylinder moves forward or extends any appreciable amount the packing in the cylinder is bad.

It will move forward because the oil is by passing the packing creating pressure on the blind end of the piston. Since the blind end has more surface area, because the rod takes up part of the area on the rod end, the piston will move forward even though you are trying to make it move rearward.

Hope this helps some.

Great diagnostic directions, I'll write them down for future reference, appreciate your time to reply. After leaving the dealer I cleaned everything on the valves and body, the O-rings, the grooves they lay in and every surface, even blew out the cavities with low pressure air. Put it all back together, sat down and prayed. Lord if you really think I need to learn how to rebuild a cylinder, I can figure it out with your help and the Orange Tractor website, but I'd really appreciate it if you'd just make it work now instead of later. Fired it up, hit the level and up came the blade.

Orange tractor website advice and a little prayer,....Lucky in Kentucky.

Any ideas concerning what was wrong in the valve body that taking it apart, cleaning and reassembling would do to fix it, outside of prayer of course?

Thank you to all. Now,..... let's go push a little dirt!

 

[Big Kahuna]

Any ideas concerning what was wrong in the valve body that taking it apart, cleaning and reassembling would do to fix it, outside of prayer of course?



Dirty..................the easiest to fix............give her hell

Big Kahuna

 

[North Idaho Wolfman]

Yep one stuck or dirty part in the valve will do some strange things to it.