Hi, uisum,
This hydraulic system is a pressurized system - that is to say that it stores pressure in the tank to help feed the pump. If the seal ring inside the cap is defective or if there are leaks in the suction line, that pressure can leak away partially or completely, which leads to the pump not getting the full oil feed that it needs to function properly. This COULD be a contributing factor to your problem.

How-wevver, your description of the wear and scratching on the pump parts leads me to suspect that your main problem lies with a worn and/or damaged pump. IF I am right, there will be metal in the filter and maybe metal throughout the system depending on the severity of the wear and/or damage. I would suggest removing the filter and cutting it open to see how much - if any - metal is trapped there. This may give you a clue about how much cleaning and flushing you need to do - if any.

Just my 0.02.

Hi, uisum.
Your latest photos were not showing when I typed my last reply but, now that I have seen them, they tell a story. You need at least a new pump kit consisting of rotor with vanes and the 'stator' as you call it. You also probably need to have the end plates resurfaced to completely flush as it takes VERY little space for oil to bypass in a hydraulic pump. New seals would also be a good idea, indeed a MUST.

Just my 0.02

The Cat hydraulic systems run closed pressure systems. Not to feed the pump but to provide an air cushion to prevent/reduce hydraulic shock to the system.

that should be a vickers vane type pump vickers is now part of eaton. parts are readily available. your local cat dealer will also have parts. if you have a parts book that makes things much easier.

the end plates need to be surfaced either take em to a engine shop or you can do them yourself with wetndry sandpaper and a piece of flat glass you also need a old towel to lay on the bench to cushion the glass. you get 300 grit sheets and one at a time wrap the edge under the glass this holds it flat and keeps it taught dampen with water and detergent solution have some in a squirt bottle.

place the plate face down, pressing with light and even pressure, and move it back and forth turning it a little after the 3rd or 4th stroke when you think the sanding pattern is even over the whole surface coat it with engineers blue and repeat until the engineers blue is gone.

NOTE: the wetndry sheets must be bigger than the part being surfaced or it wont work and will need to be taken to a engine shop to be surface ground. and it must be a single sheet. change sheets as needed but before they wear through the grit. keep the paper lubricated with water solution. when finished wash well with kerosene and wipe dry.

That looks like a cartridge style pump. Put a new cartridge in and it will be good as new without replacing the entire pump. OM should be able to tell us if there is a cartridge available. I don't have a parts book for that model.
That damage is caused by the vanes hamering and bouncing (chattering) the surface of the ring or stator. Not the type of damage usually caused by cavitatoin but mechanical damage and cavitation can go hand in hand at times. This article gives a good idea of the possible cuases.
 

Hi uisum,
now we are getting somewhere as your cam ring pictures show a badly wear stepped vane running surface worn out due to abrasive wear and so your pump cartridge is worn out and needs a new one fitted.
As the vanes pass over the wear steps they lose contact and any pressure they are pumping escapes and makes the noise you hear and can aerate (cause the oil to be filled with air bubbles) the oil as your pictures show.
Suggest also to fully change your hydraulic system oil as it is dirty oil usually from worn scored chrome cylinder rods and failed rod wiper seals that cause most dirt to enter the system.
Filling the system using dirty funnels and oil cans also is a cause of dirt in the system.
Do the oil tests as suggested above to prove to your self that you have aerated oil--full of little air bubbles or not--if it is water then that causes the oil to degrade and loose its wear resisting quality and wear occurs as seen.

Cheers,
Eddie B.

Hi guys ,
infinitely thanks to all. Now I have cleared my mind about what happened. Not long ago I made a video of this old cat. In order not to get bored watching the whole video, at minute 3:33 you can notice a leak of oil from the tank and the color. From the minute 8:34 you can clearly hear the noise of the pump.


 

8 Months ago a new cartridge kit from ITR cost me about €400. They are readily available. Make sure you get the correct GPM kit for your serial number.

The loose capscrews that hold the mounting plate might be the result of a chattering pump causing vibration.

I'll replace the oil and filters, and a new aftermarket pump cartridge. The pump is a vickers. I think the cartridge fits this 7J0559
The serial number of the 951c is 69h3944

Be aware there is more than one pump and cartridge used on the 951C based on tractor s/n.
My parts manual is for the US version 86J so I hesitate to supply part number for the unit used on the France built 69H. Even safer would be to go by the Vickers numbers as who knows what resides on the machine now.