There is 2 nuts and a couple of spring washers that make the lever have tension, included a picture of them.
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You have a simple hydraulic system , Pick-up screen/filter screen, suction line, pressure line, control valve and relief valve.
The control valve is almost always blamed for problems but almost always isn't the problem.
Common problems are:
1: Bypass valve is turned in the open direction, (most models have a valve under the seat that bypasses the three point control to give you and optional power port), look for valve handle.
2: Bad/old/plugged screen and fluid, Replace screen and fluid. and do #3 at the same time, when fluid is drained.
3:Cracked suction line or bad rubber hose,(suction line is the large line that goes to the pump), pull and inspect for cracks, wear spots, and bad rubber connection (it can look fine on the outside and be collapsed or split on the inside.
4: Stuck relief valve, pull and clean and replace any O-rings.
4: last and least, pull the top off and rebuild the valve and the cylinder.
If you include some pictures of the valves under the seat I can point out the bypass if you have it.
NIW, I have a similar issue with my 3 point hitch. First, a little background so you have complete picture.
The three point hitch was working fine until the supply and pressure lines were removed from the pump. This was done to gain access to the block in order to plug an engine oil leak.
The lines were replaced, oil added to proper level. Tractor operated correctly for 4-6 hours then stopped.
I have read most, if not all, threads on this forum regarding this issue and have done the following...
1) Drained and changed the hydraulic fluid, actually 80/90wt oil
2) Removed and cleaned the hydraulic screen.
3) Removed the supply line from both the pump and the housing sump and used compressed air to blow it out.
4) Did the above process to the pressure line also.
5) Removed the relief valve, cleaned and inspected it for scratches. (This part is discontinued as are the internal components) Then reassembled it.
6) Removed the entire upper rock arm housing, cleaned, inspected and replaced all the O-Rings, Backing Rings, and springs in the control valve, the shaft O-Rings and the piston O-Ring and backing seal. Then reassembled.
Once everything was reinstalled, the lift arms came up and held a load. Once they were lowered, they failed to lift again.
This tractor has a hydraulic lift cylinder that raises and lowers the front sweeps. This cylinder has sufficient pressure to lift the arms with me standing on them. ( I weigh over 200 lbs )
I don't think it is the pump as I have plenty of pressure to operate the front hydraulics.
I tried adding a picture but I do not have enough posts, yet.
I read in a previous post that bypassing the front hydraulic cylinder would aid in trouble shooting. I disconnected the lines and looped one of the lines back, thus bypassing the front cylinder. The 3 point hitch still did not function.
I have adjusted the knob below the seat to both extremes and counted the turns to ensure the "middle" position. The 3 point hitch doesn't work in any position.
I did remove and clean the breather tube. No joy with the 3 point hitch.
Any suggestion or comments would be greatly appreciated.
Semper Fi