Posted by JDseller on September 03, 2012 at 16:28:23 from (208.126.196.144):
In Reply to: 7700 JD 3 point posted by LazyWP on September 03, 2012 at 06:23:01:
The rock shaft sticking was a common problem on one that the owners rarely used the three point. The lift arms hook to a cross shaft that is just a pivot in a housing. The lifting force is done with the external lift cylinders. The draft is all electronic and it picks up the traction load electronically in the bottom lift arm pivots.
The lift cylinders are single acting ones. They depend on the weight of the three point lift arms to lower itself.
First thing to do is see how hard it is stuck. I have been able to put weight on the lift arms and get them to go down. I do mean WEIGHT I usually started out with a ton of suit case weights. I have a bracket made to hang on a quick hitch that hoods front weights. IF they will go down I lube everything up that I can get grease too. I then spray the cylinders down too. Then just work it up and down until it frees up. Most of the time if it is going to free up it will do it in the first few minutes. You will see it getting better.
IF it will not go down I then leave the weight on the lift arms. I hook my engine crane to the weight bracket. I hold the weight up off of the lift arm pins with the crane. I then remove the lift cylinder pins. I lay the lift cylinders to the side out of the way. I let the weight down on the lift arms with the engine crane. Most of the time the cross shaft will move in the top pivot housing like it should. Just grease and spray while working it up and down. The cross shaft will usually free up pretty fast.
Now you need to see if the lift cylinders are stuck. Take the hydraulic hose off the cylinder. Drain all the oil you can. You will be making a mess any way later. Try pulling them in with a cable come along. I have had to use a press to get them to move. If they are stuck this hard then you will need to tear them apart and rebuild them.
You will need to get me a serial number as the lift cylinders come apart differently by serial number. There is internal snap/retaining rings you have to get out before the rod will come out of the bore. When you get the retaining rings out it can still take a lot of force to get them apart.
I have a home made hydraulic press. I used double acting cylinders. I can chain something to the bottom and pull with the cylinder. I have stalled a 4 inch cylinder pulling them apart. I had one set that we never could get apart. We junked them trying to get them to come apart. I had a set that we hooked one end to a 36 inch diameter oak tree and a Cat D-8 to pull with. They came apart but we bent them doing it.
The bore seals will get water in behind them and then rust. This rust pushes the seal out against the cylinder rod just like a brake. It make then bind up.
The real sad part is that if the owner had just cycled the three point up and down a few time each oil change they would never have stuck. In the last dealership I worked at we had a service check list and it included cycling the three point hitch ten time.
The top picture is the rock shaft cross shaft. The second is just the lift cylinder. !!!Caution!!! There are serial number break on both these parts so make sure you have yours when getting parts and service instructions.
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