860 hydraulic problem, need diagnostic help.

Here's the problem. The lift arms will slowly go down if I shut off the tractor with the lift in the up position and a bushhog, plow, or any other attachment hooked up. It usually takes about 5 minutes, maybe a little longer for it to bottom out. If I leave the lift in the down position when I shut off the tractor, the lift ususally will not work again when I restart it. I have discovered that if I bleed the hydraulic pump by loosening one of the pipe plugs in the top of it, some air will come out and after the fluid starts I tighten it down and the lift will work.

This weekend I replaced the o-ring and leather seal on the lift cylinder piston. I replaced all of the o-rings on top of the lift cylinder, and I replaced all of the o-rings under the remote hydraulic plate forward and in front of the seat. I of course changed the fluid and replace it with 134 from my local NH dealer.

What is the problem? I have no clue.

Thanks a bunch,
Gil

No, it doesn't fall 6"-12" and then stop. It falls all the way to the ground. The rate of descent seems to be constant too.

I will go the the NH dealer tomorrow and try to get a new safety valve, install it, and see if that fixes it. I did notice something on the safety valve that was peculiar; the nut on the top of it is spot welded to the body of the valve, I assume some idiot did this instead of using Loctite or teflon tape. Some people should not be allowed to own tools. LOL

I have owned this tractor for the past 4 years. I know this tractor's history for the past 13 years. This has been a problem with this tractor for as long as I can remember, and I know for a fact that the previous owner didn't spot weld it, or even turn a wrench on it. Heck, I had logged countless hours in the seat of this tractor prior to my buying it. Why am I telling you this? Shoot, I don't know. But I did, so there you go.

Again, thanks Brad.
Gil

Gil

Bleed your pump at the pump and if that doesn't fix it, look for air entering the system between the suction from the fluid sump and the pump. O-rings are prime candidates and don't forget there are 2 where the lid fits onto the tractor housing.

Mark

Mark, yes I replaced the 2 o-rings under the lift plate when I serviced the lift plate this weekend. I talked to a buddy a work that collects antique tractors, he probably has close to 30, and he said the same thing about the jerking being air. He also suggested that I check the hydraulic manifold where it attaches to the reservoir, and also where it attaches to the bottom of the pump.

Like me, he had never had one of these apart, but he thought that the check valve would be located where the hydraulic manifold attaches to the reservoir. Is this correct? Both of you gave it the same diagnosis.

I'm going to my NH dealer tomorrow, going to buy a check valve, probably a safety valve, and of course o-rings for the manifold.

You guys have all been a big help, Dave, Brad, and Mark. And I sincerely do appreciate it.

Gil

Can't help with valve location as I never had to change one (they were never my problem). The I&T manual shows functionally where it is.

I know that one of them is in the front of the cover plate (right between your legs on top of the housing). You can't remove it without taking the cover plate off as the mounting flange (where the tranny and hyd sections mate) is in your way. I&T manual tells you which one this is.

There may be one more place to suck air. Your tractor may have a filter screen (not filter per se, as they are usually on the discharge tube) in the sump, on the floor, on the right side.(just under and inboard of the 2 cover Orings we discussed.

If this screen is clogged with crud, your pump can be sucking fluid but not getting all it wants. That lowers the atmospheric pressure of the oil and it "boils" so to speak. This creates a flood of tiny bubbles that could cause this problem.

I have been into sumps from 2N thru 4000 so I don't remember which had filters and which didn't.

If all else fails, this is something to try.

Also (again not remembering the setup) if you have tubes (cast manifolds/combination of both) coming from the hyd section to the pump inlet/outlet, there are Orings at both the housing and pump interfaces that could be your problem.

Good luck.

Mark

Brad, thanks for clarity on the location of the check valve and safety valve. I'll try the check valve first, while I'm at the NH dealer, I'll ask them about whether or not there is a screen in there.

Man, this forum is great! I've learned alot about my tractor here.

Gil

I agree, as no one is around to help me pull the lift cover either.

Mark