3pt doesn't stay raised after engine is shut off

[Dan707]

This problem just developed on my 1984 Ford 1910 1665 hours. Hydraulics for the FEL and the 3pt work great with the engine running but shutting it off causes the 3pt to lower to the ground. Any leads on what to check first?
Thanks

 

[J_J]

The only place for the fluid in the cylinder to go is back through the valve spool, or through the piston seals.

 

[vtsnowedin]

What J-J said. Depending on which O ring or seal is blown it may get worse until you fix it. My 5045E got so it wouldn't pick up 300 lbs with the 3pth. Nothing $900 in dealers shop time won't fix.

 

[LD1]

Yep. Valve or piston seal for the 3ph. The position control of the valve holds it up as long as the engine is running and the hydraulic pump is pumping.

Not familiar with that model but a lot of newer tractors have a 3ph drop speed adjust knob. If so equipped, you can close that off. If the 3ph still drops, its the cylinder. If not, its the valve.

 

[Egon]

If it does not affect your use of the equipment just carry on as usual. Most equipment will leak down as the hours and wear accumulate.

 

[cormier]

Lower your attachments to the ground when you park your machine. Its relieves the pressure on all the seals and they will last longer that way. And its much safer also. If a hose blows or seal and it crashes down on somebody!

 

[Gunny]

Lots of the smaller Kubota tractors have an o-ring on the lift cylinder that can eventually wear out. It's not a huge deal to replace, but it does take some time. As long as it was lifting while running, I'd let it be.

I also agree about never leaving any implement suspended when the tractor is parked, no sense in putting any more strain on stuff than it has to go through.

 

[Dan707]

Lots of the smaller Kubota tractors have an o-ring on the lift cylinder that can eventually wear out. It's not a huge deal to replace, but it does take some time. As long as it was lifting while running, I'd let it be.

I also agree about never leaving any implement suspended when the tractor is parked, no sense in putting any more strain on stuff than it has to go through.

It does have the control knob. I believe its all the way screwed in already but will check

Its not a huge problem that it does it but sometimes I need to inspect the attachment with it up or adjust the sway.

Thanks all

 

[ovrszd]

If your control knob is screwed in all the way the 3pt won't lower.

As far as valve versus cylinder. A few months ago I would have said it can be either. But after a lengthy discussion here on TBN I have been educated. It's impossible for the cylinder to be the problem. It's the valve. Hopefully no one will ask me to explain that, cause it will take several pages of posts. But it's true. Unless the valve lets the oil escape back to the tank, the cylinder cannot drift down.

Be nice everyone. Let's not sling mud as my Dad would have said.

 

[cormier]

If your control knob is screwed in all the way the 3pt won't lower.

As far as valve versus cylinder. A few months ago I would have said it can be either. But after a lengthy discussion here on TBN I have been educated. It's impossible for the cylinder to be the problem. It's the valve. Hopefully no one will ask me to explain that, cause it will take several pages of posts. But it's true. Unless the valve lets the oil escape back to the tank, the cylinder cannot drift down.

Be nice everyone. Let's not sling mud as my Dad would have said.

You are right it would be the valve. If the cylinder is bypassing and the valve is good their is no place for the oil to go so it wont move.

 

[J_J]

Are you really saying that bypass fluid from a worn piston seal can not leak into the crankcase?

I sure thought that must all 3pt internal cyl's backsides were open to the sump.

If a piston seal is perfect, the only way fluid can get back to the sump is through the descent valve, or a bad valve spool, and yes, it will block the fluid if you want for transport.

It is also used as a variable descent device.

If you close off the descent valve, you close off the 3pt valve as being the problem.

 

[vtsnowedin]

Are we considering that there is a relief valve in there that may have failed plus a number of small O rings that if failed let oil drain back to the sump?

 

[ovrszd]

You are right it would be the valve. If the cylinder is bypassing and the valve is good their is no place for the oil to go so it wont move.

Bingo. Took me a long time to understand that simple fact.

 

[Leejohn]

I'll just say one thing, there is no oil on the rod side of the piston.

 

[ovrszd]

Are you really saying that bypass fluid from a worn piston seal can not leak into the crankcase?

I sure thought that must all 3pt internal cyl's backsides were open to the sump.

If a piston seal is perfect, the only way fluid can get back to the sump is through the descent valve, or a bad valve spool, and yes, it will block the fluid if you want for transport.

It is also used as a variable descent device.

If you close off the descent valve, you close off the 3pt valve as being the problem.

I want to stand corrected here. In my earlier post I was thinking a 2-way cylinder. 3pt systems use a 1-way cylinder. The rod end of the barrel dumps to atmosphere. In that regard it is truly possible for the cylinder to leak down caused by cylinder piston bypass. In a 2-way cylinder situation that is not possible if the valve holds.

Good catch JJ

 

[ovrszd]

I'll just say one thing, there is no oil on the rod side of the piston.

In a 3pt system or 1-way cylinder system, yes that is correct. As stated above, I was thinking of a 2-way system.

 

[J_J]

There are some tractors with external hyd 3pt lift cyl, but I don't know if they are SA or DA.

Anybody know?

 

[flusher]

There are some tractors with external hyd 3pt lift cyl, but I don't know if they are SA or DA.

Anybody know?

My 1951 Minneapolis Moline BF tractor has a DA hyd cylinder on the 3pt. Also my 1951 Farmall Super A which has been retrofitted with a 3pt that has a DA hyd cylinder.

 

[ovrszd]

My M9540 is external but they are SA. They have a soft hose on a fitting at the rod end to let them breathe clean air from the rear axle housing.

 

[J_J]

So, if your cyl seals ever leak, where do you think the fluid will go?