Ford 4000 lift problem

Hi, I have a 1968 Ford 4000 3cyl gas. I've had it for close to a year. It always took the 3pt a while for it to start working. When I say start working, it doesn't lift up regardless of what you do with the lift control lever, or if it is in position vs. draft mode. (It does go down so it isn't stuck in the up position). Weight on the lift arms doesn't matter. Sometimes revving the engine would help. Once it works, it works great and can hold up heavy attachments for days. But now it seems to take much longer to start working. Yesterday I had it at a fast idle for 30 minutes before the lift arms up decided to raise up.

I have had the lift cover off and replaced o-rings around the cover with the intent to replace the filter and clean the pump screen. But I discovered these were not accessible without splitting the tractor... so I left the filter and screen be for now, other than trying to flush the surface of the screen where I could see some crud.

But since the lift, once working, is not sluggish and works perfectly, has me wondering if it could be a valve sticking instead of a clogged filter. Any thoughts on this? Also, if it is a valve, would that be more readily accessible to replace than having to change filters and splitting the tractor?

Thanks!

My 4 cylinder 4000 does that, it's a sticking unloading valve. i think yours is similar to it. Look for a part explode on your model and see if it has one.

Thanks riveroadrat. Usually I use the New Holland website to view the parts diagrams. It looks like NH changed their website. Can't say I like it, and many of the numbered parts on the diagrams are no longer described in the accompanying parts list. Maybe they decided to omit the "no longer serviced" items. But that would suck since it was still useful to at least have a description.

That said, is the "back pressure" valve the same as the "unloading valve?