Aaargh! 3-pt hitch not lifting any weight.

[Leejohn]

Here is some good reading on your 3pt. http://www.tractorbynet.com/forums/...y-lseries-3pt-hitch-fixed-18.html#post2472447

There is 2 or 3 O rings under the valve, one of them might of blew out.

 

[project_X]

Here is some good reading on your 3pt. http://www.tractorbynet.com/forums/...y-lseries-3pt-hitch-fixed-18.html#post2472447

There is 2 or 3 O rings under the valve, one of them might of blew out.

that makes sense, I just need to get a nice diagram of my valve, so that I can put it together after I get it apart.

 

[Leejohn]

You might try this. Go to the John deere web site and look up the parts manual for a John Deere 750 and see if it looks like your valve. That is a 20HP, but don't order parts from there because it might not be the right match
for your tractor.

 

[project_X]

You might try this. Go to the John deere web site and look up the parts manual for a John Deere 750 and see if it looks like your valve. That is a 20HP, but don't order parts from there because it might not be the right match
for your tractor.

thanks, i tired that yesterday, no luck.

 

[284 International]

J_J, I tried closing the lock valve on two of my Yanmars and then attempting to raise the three point. Both immediately went into bypass. This is true whether the implements were up, down, or in between.

I'm really too ignorant about this subject to be of much help, but I'm interested in learning. It seems to me that the flow of the pump is going to be constant at a given RPM. It is capable of developing reasonable working pressure, since he can get pressures of 2000 psi or so on his gauge.

When he is trying to operate his 3 point lift, he can only get pressures of about 450 psi, but only at maximum pump RPM/volume. Anything over around 450 psi, by my reading, won't let the system lift the load. In my limited understanding of how these things work, that seems to imply that there is a restriction to flow in a bypassing system that is restricting the flow of fluid to 450 psi at, say, 4 gpm, thus pressurizing the lift cylinder to that as well.

If that is true, the choice seems to be whether there is a stuck or weak bypass valve, or if the control valve itself is passing fluid.

Is that correct?

A tangential thread-jacking question: Say the lift piston seals are leaking fluid. Where does that leaked fluid go? Is there a return line on the non-pressurized side of the piston to the reservoir? Does it escape out the vent when sufficiently accumulated?

 

[project_X]

here is a diagram of my valve assembly

any place i should start?

 

[Leejohn]

I found a valve that is almost like yours and it was on a JD 790. I would start at the 3 o rings then to the poppet under cap #7 and #10. That valve under 7 goes all the way to plug 10. If it was me I would take the hole valve apart now that you have the brake down. If # 10 is a hex plug then you should look at the JD790 parts list, also you can read the parts names. I'm sure you checked lever linkage of anything loose or broken right?

 

[J_J]

284 International,

GPM's , only dictate the speed of operation. The resistance to the hyd fluid is what builds pressure, such as when you try and lift a 1000 lb load, or you raise the 3pt lever and cause the 3pt cyl to fully extend. If the relief doesn't come on, then the cyl is probably leaking. When the cyl leaks, it leaks into the sump. If you can't build pressure by raising the 3pt lever, something is leaking. If you can make the 3pt go into relief, then you should have enough pressure to operate the lift.

I would first remove the components for the lock down knob and inspect and clean it.

The 3pt valve or the cyl could be leaking.

I believe you verified about the lock down/ descent knob. If closed, no fluid in or out.

 

[284 International]

I'm not trying to be argumentative, I just don't understand where the fluid could be going.

Is it correct to say that A) If the lock valve is closed, the fluid isn't going through there, and B) If the implement will stay raised, it isn't leaking past the cylinder?

 

[project_X]

I found a valve that is almost like yours and it was on a JD 790. I would start at the 3 o rings then to the poppet under cap #7 and #10. That valve under 7 goes all the way to plug 10. If it was me I would take the hole valve apart now that you have the brake down. If # 10 is a hex plug then you should look at the JD790 parts list, also you can read the parts names. I'm sure you checked lever linkage of anything loose or broken right?

i've inspected the linkage, and don't see anything that looks out of place or broken. the lift does lift minimal weight, if I get the volume of flow high enough. at low volume it won't lift, but will hold position.

 

[J_J]

If the knob is locked down, the fluid has to go through the 3pt valve via the relief valve. If the relief valve is supposed to open at 2000 psi, but it is weak, rusty, or whatever, and it is now relieving at 500 psi. That means that the 3pt will only work at and lift a load equal to the 500 psi.

If the 3pt can lift and hold a load, that means that the cyl is probably good. If you should happen to keep adding more weight on the 3pt, the safety valve will activate.

If you raise a load and locked the knob down, and the 3pt drifts down in a short time, then the only reason for this would be a leaking cyl.

 

[project_X]

If the knob is locked down, the fluid has to go through the 3pt valve via the relief valve. If the relief valve is supposed to open at 2000 psi, but it is weak, rusty, or whatever, and it is now relieving at 500 psi. That means that the 3pt will only work at and lift a load equal to the 500 psi.

If the 3pt can lift and hold a load, that means that the cyl is probably good. If you should happen to keep adding more weight on the 3pt, the safety valve will activate.

If you raise a load and locked the knob down, and the 3pt drifts down in a short time, then the only reason for this would be a leaking cyl.

JJ, Have a look at this drawing of a similar yanmar, I don't know if that is the same as other brands 3pt hitch circuits. If the control valve has a leak between the HP and Tank ports, I believe the relief valve will not trip in this situation.

Both my safety and relief valves looked to be in very good shape, i installed extra shims in each to see if that made any difference, but no luck.

The knob did stop the arms from going up/down (in the closed direction) and fall very quickly (when the lever was pushed down) in the other direction.

I really want it to be something other than the control valve, but the results of every test seem to point to an internal leak in that valve.....

 

[J_J]

Close the knob [ N ], and insert a hyd gage at [ Q ]. raise the 3pt lever, and that should provide pressure to test valve.

This should test the 3pt relief, and the 3pt valve for leakage. [ L ] is the 3pt relief.

If you read a high pressure, and the relief valves activates, that proves the 3pt valve and relief are good.

 

[project_X]

Close the knob [ N ], and insert a hyd gage at [ Q ]. raise the 3pt lever, and that should provide pressure to test valve.

This should test the 3pt relief, and the 3pt valve for leakage. [ L ] is the 3pt relief.

If you read a high pressure, and the relief valves activates, that proves the 3pt valve and relief are good.

I get the same results at both [ Q ] and at [ J ]. low flow 250 psi, high flow 500 psi. Regardless of the shims in the relief or safety valve. The springs look good, balls and seat look clean as well.

 

[J_J]

Did you say you had good hyd pump pressure, and what was it in case I missed it?

At the low pressure you saw, the relief would never come on, and you will never raise much of a load. But of course you know this.

Did you test the cyl, by raising the 3pt and closing off the lock valve , and then loading the 3pt with some more weight. You should be able to test the cyl pressure at port [ U ].

 

[project_X]

Did you say you had good hyd pump pressure, and what was it in case I missed it?

When the loader or the remotes are hooked up, I see a relief pressure in either of those valves of 2200psi or so.

With just the 3pt hitch operating i can only see a max of 500psi when the flow is high (2000rpm).

 

[J_J]

If you test the cyl, you can eliminate it as the cause, and that should indicate that the 3pt valve is not working properly.

I am assuming that you maxed out the valve in the raised position to work the cyl by applying fluid so the cyl can develop pressure.

The pressure is determined by the amount of resistance the cyl provides, but the potential pressure can bleed off before it gets to the cyl, as in worn 3pt spool in the valve, weak relief valve, weak pump, but you say the pump has developed about 2200 psi, so that is what you are supposed to see at the back if all things are working correctly.

 

[284 International]

Is there a relief on the valve itself? The diagram shows a return line to the reservoir. When is it carrying fluid?

It seems like the valve is the culprit.

 

[project_X]

Is there a relief on the valve itself? The diagram shows a return line to the reservoir. When is it carrying fluid?

It seems like the valve is the culprit.

The valve is basically over the reservoir, there is no relief valve on the valve itself just the body of the housing.
I believe the return line of the valve carries fluid when the lift reaches its specific height from the lever position. I think there is a leak between high pressure and this return....

I will likely pull it apart over the weekend to inspect it.

 

[project_X]

I found a valve that is almost like yours and it was on a JD 790. I would start at the 3 o rings then to the poppet under cap #7 and #10. That valve under 7 goes all the way to plug 10. If it was me I would take the hole valve apart now that you have the brake down. If # 10 is a hex plug then you should look at the JD790 parts list, also you can read the parts names. I'm sure you checked lever linkage of anything loose or broken right?

I never would have though to look at the 790, I had concentrated on similar model years as my Yanmar.

I managed to get a shop manual for the 790 with excellent diagrams and procedures. I will post some pictures and drawings when I get it pulled apart.