rebuilding the hydrualic diverter valve on a d4

All options are possible.
Not sure which is the easiest to start with testing on but the ram test is to extend and hold the valve open on extension and see if the ram heats up in the area of the piston, and simiilarly retract and again test for heat in the area of the retracted piston.

For the diverter valve, does it have the second output circuit plumbed to anything or is it blanked off? If blanked off, then you know that it's at least not leaking into the second circuit so could only be leaking between the up / down ports. Trying to remember and I think that there might be an o-ring on the valve stem between the two circuits. If so, then if it's in good shape, that would prevent bleed between the two. They're easy to disassemble so probably worth opening up and taking a look, unless you already have.

I don't know what the test would be for the valves in the hydraulic control other than it's the only option left after testing the two above (beyond an external leak which I would think would be obvious).

When I did my D2, I replaced all o-rings in the hydraulic control (#44 single spool) and the diverter valve (blanked off to rear) but did not touch the rams, and the blade holds for more than minutes. The o-rings were there but all hardened so I'm guessing it would have leaked if I had used it as-is.

Hi Team,
alas, the D4 Cat blade lift cylinder pistons have by pass valves in them that prevent hydraulic lock at each end of the ram travel so doing a hydraulic stall test in this way is not possible as the valves open and so bypass back to tank.
The blade needs to be raised and set in the hold position, with the engine stopped, the now non pressurised blade lower mode lines are disconnected to check for by pass as the blade goes down ---opposite can be done by raising the front of the machine--engine off-- remove and check raise mode lines for bypass.
A further test we did is to block the blade up and remove the lift lines as well then apply blanking off plates to the lift ports on the cylinder--apply blade weight back on the cylinder and back off the block--or better still is to lower it with a hoist to check the cylinders only--previous test still had part of the system in the circuit and so give false test on the cylinder and so is usually done as part of a two part test.
Be aware that the standard piston seals on these are fiber rings, usually with large ring gaps that bypass.
Non centralised and/or worn or scored spool valves and lands on the valves and/or in the housing bores can be another issue too.
Likely others that do not come to this tired mind at present.
Cheers,
Eddie B.

our cousin re shafted the rams for us, I know he replaced the vee packs and shaft seal whether he did the piston seal I'm not sure I imagine ray would have checked them for damage.
unsure what model rams they are as she was originally a farm crawler and had the dozer attachment added later. question is how do you identify them i have a hyd parts book but dont have serial numbers for the hyd unit.

what makes me think of pump issues is the pump can be heard cavitating yes vane pumps are noisy.
and i know i need to replace the valve actuator shaft bushes so could that be part of it too.

neil you are correct there is a o-ring but its at the top of the diverter spool so it would only seal the top plate so it could bypass internally.
and the other ports are blanked off. hence the question would adding a o-ring groove between the ports stop this.

so it looks like i have some work to do.

gentlemen, thanks for the info and ideas.

chris.

Check the cylinder part number, early cylinders are 3Fxxxx, late cylinders are 8Fxxxx.