'65 Ford 4000 hydraulic/PTO stops working

Recently encountered an issue with our '65 Ford 4000. It has a front end loader on it, and has (what I think was added?) the twin lever unit, one to control a set or rear remotes and one to switch between powering the FEL and the 3-pt arms. Everything in this respect has worked fine for the two years we've had it. The only equipment I've thus far used with the tractor is a manure spreader and a 3-pt NH 615 disc mower (5 discs in a sickle-bar type setup, can raise and lower the blades). Mowed a few fields last year, all went okay.

Few days ago, mowing for the first time this year, after a couple hours the hydraulics started to seem sluggish - the mower on the 3pt, or the mower arm on the remote, wouldn't lift right away. And the couple times I needed to restart the PTO, there was a delay as well. That evening, mowing a different field, things seemed to get even more sluggish, and then finally (with everything running) the PTO quit, and I lost all hyrdraulic power as well (couldn't raise anything).

Well, wound up parking it for a couple days, went back today to check the oil level, was good, started it up, and everything was working. Gave it a bit of a test, and sure enough after about 20-30 minutes of mowing, things got sluggish again. Tested the FEL, and it was slow to move and sort of hopping as I raised it.

Consulting the shop manual, looking at troubleshooting for both the PTO and the hydraulics, the 3 issues in common that come up are oil level, control valve, or an issue with the pump. Its not oil level, and it seems to be related to heat.

Never experienced this last year. Did change the rear axle oil a week or two before mowing. (And now remembering, the shop I got it from sold me oil from their shop drum, filling containers they had on hand, and one of them had some kind of sediment in the bottom that I only saw when pouring it into the tractor...)

If something with the control valve or hydr pump, what it is about getting hot that causes things to shut down? And is fixing it something for a shop, or can it be DIY'd? Feedback much appreciated!

I would put a cheap gauge on it and see what kind of pressure your pump is making.
Wouldn't be hard to hook it to one of your remote lines and see.
They sell them here on this site but it says they're out of stock.
But they are available from Northern Tool ($20), probably Amazon or Ebay or even, gulp, Harbor Fright.
Those pumps are pretty reliable but after 49 years you never know.

OK, tested the pressure off the remotes after cold start - reading 1850-1900 psi. Is this low to begin with? But I haven't run it hot and checked, when things start to give out. Whatever it is, it looks like the only thing to do is start poking around the system?

What's more likely - the pump starts failing because it heats up, or a valve starts sticking?

And it sounds like if I'll be taking the top cover off, I should have a new set of O-rings on hand to replace those when doing so?

(quoted from post at 10:53:38 07/04/14) OK, tested the pressure off the remotes after cold start - reading 1850-1900 psi. Is this low to begin with? But I haven't run it hot and checked, when things start to give out. Whatever it is, it looks like the only thing to do is start poking around the system?

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1850-1900 psi is on the low side, especially when cold. It should be up around 2200 psi.

What's more likely - the pump starts failing because it heats up, or a valve starts sticking?

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Neither. If the pump is failing, it's not failing because it warms up, and a valve usually sticks when it's cold, not when it warms up. You likely have an internal leak somewhere, either inside the top cover, or inside one or both of the two valves on top, or inside the pump itself. The symptom gets worse when it heats up because when it is cold the fluid is thicker and the system can still provide adequate pressure. As it warms up the fluid gets thinner and so the leak gets worse and the system can't maintain adequate pressure.

And it sounds like if I'll be taking the top cover off, I should have a new set of O-rings on hand to replace those when doing so?

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as I said, it may be something inside the top cover that's leaking, or it may be internal to the pump itself, or it's possible that it's one of the two valves on top of the top cover that's leaking internally. You'll have to decide which to tackle first, but yes, if you remover the top cover you should get a top cover repair kit to replace all of the o-rings and seals inside.

Thanks Sean, yes, I can find a leak at the top when I engage the remotes. Will try new rings and seals overhaul. Is it worthwhile to replace the filters or anything else in there while I have it opened up? For all I know the filters are 50 years old.

There is a screen built into the end of the pickup line that is meant to be cleaned and re-used. There is a cartridge type filter on the return line that is meant to be replaced.

Just to update, it all turned out to seemingly be a pretty simple issue - the small supply tube from the gear hydraulic pump to the PTO control valve had become disconnected somehow - the threaded nut that screws into the valve housing to hold the flanged tube in place was off. WHY it was off, I don't know...
I didn't change any filters, since it seems I'd have to split the tractor just to do so. The PTO and drive shafts that run through the hydraulic housing block their removal, at least the sump intake filter. There was a lot of paint flecks and filings on the filter, I sprayed it off with diesel as best I could to try to drain some out the drain plug hole.
Anyway, mowed for a couple hours last night, everything working so far.