851-Strange Hydraulic Problem

M-MAN

Well-known Member
Location
Bostic, NC
I'm having a won't work until it's hot problem with the lift on my 851. Let it run about 45 minutes and it works just fine.

I changed the utf along with hp tranny line and manifold seals(NH) back in the spring and it worked great just as soon as I fired it up. I haven't used it all summer and now she's acting up until it runs a good while.

Fire it up and there isn't much drag on the lift handle like there is no pressure for a few minutes. Then you can feel the drag but no lift. Loosen the pump bleed screw and oil is pushing out. Remove the filler cap and look inside for an oil spray. There isn't one from anything - check again after lift starts working and there still isn't. It has to be a pressure problem but is it a pump or stuck valve? With it not working at all when cold and working fine 45 minutes later I'm stumped. Hopefully one of you guy's have seen this before and can point me in the right direction.
 
Sounds like a sicking control valve and when the oil is hot it frees up and works.
 
I'm thinking Old may be on the right track.

if you have oil flow at startup, but no lift.. that's leaving you with looking at a sticking valving issue.

if you have remotes.. check them, but if not, we can guess that it might be just 'unloading'.

Is the oil clean.. I'm guessing it is if you just filled and repaired it in recent history.

If you have some naptha, I think I would cut your utf oil with a quart or 2 of it and then go run it.

the naptha will thin the oil like diesel or mineral spirits, but it will flash off with use decently quick after this test, and not leave you with thinned oil , eventually.

If the naptha thinned oil, after running it thru, then shutting down, provides you with good restarts the next day, etc. and the problem does not occur, might have been something gummed up or dirty.. perhaps a piece of varnish, glaze or emulsification broke free and hung.

if it works fine for a while and then hangs again after the naptha flashes off, lets look at other issues ( we will cross that bridge when we come to it ).

If you notice any bubbles on the oil, let us know.

if you notice any water entrainment ( emulsification ) let us know.. there are seperate treatments for that depending on severety.
 

But does he have pressure? I'm wondering if its barely pumping, but due to leaky pump/tube? its taking a while to fully prime up and pressurized... Just guessing here. Maybe a gauge on the pump would answer that question and we could then move on the the control valve. I'v seen the 3000 pumps do that due to poor valve seats/ball valves.. they pump, but barely for the first couple of minutes and then pick up slowly to full flow and pressure. Sorry if wrong direction....
 
I think you are confusing flow and pressure.

1, he said he replaced the pressure tube and origns / seals.

2, he says it works fine once warmed or working.

That tells us that the pressure tube is fine, since it works once warmed, and that he has not reported sump to sump transfer after running.

If he does indeed have flow, then the system is fully primed.

those systems do not operate under anything other than a little backpressure. they run 'unloaded'. IE.. flow from the pump is dumped to the sump.

when the system is instead directed to lift a load and NOT unloaded, then the pump is seeing pressure.

He opened the bleeder... he has flow.. thus it's not a bleed issue..

the system is capable of handling pressure , evidenced by it working once limbered up.

It really does sound like a sticking unloader valve, at least without hearing any more so far.
 
Thanks for the suggestions. I'll head to town in the morning and see if I can find a some naptha.

It doesn't have a remote. There is no transfer between the sumps. Both had new fluid about 15 hours ago and the level's stayed where they were. There isn't any water and there aren't any air bubbles that I can tell. I can see what looks like a little oil vibration but that's it.

Would an inspection mirror inside the fill hole allow me to see where the oil is bypassing to the sump if the valve is stuck?
 

yes,, he opens the bleeder and has fluid... but does he have pressure? Fluid barely oozing out or fluid shooting out.. That is the problem I have seen. Barely oozing out for 5 minutes or so can be due to bad pump seats, or minor leakage in input side. And when the pressure builds up, it forces the other exhaust valves to shut instead of float, so the pump then comes up to full pressure and volume quickly and finally the unload valve gets pushed/vibrated from its bleed off position into its lift position. Just an observation I have seen on 3000s. A pump rebuild or a pump swap and problem is gone. I have had mixed success with rebuilding the pumps, mostly better. New springs, balls and valve seats and pump will come up quickly.

A frozen unload valve doesnt usually care about warming up. And when you get them working, they usually stay working. But Hey,,, I could be wrong. Ask my wife.

Could be someone replace the metal ring with a oring or something even weirder.
 
(quoted from post at 11:06:20 11/19/15)
yes,, he opens the bleeder and has fluid... but does he have pressure? Fluid barely oozing out or fluid shooting out.. That is the problem I have seen. Barely oozing out for 5 minutes or so can be due to bad pump seats, or minor leakage in input side. And when the pressure builds up, it forces the other exhaust valves to shut instead of float, so the pump then comes up to full pressure and volume quickly and finally the unload valve gets pushed/vibrated from its bleed off position into its lift position. Just an observation I have seen on 3000s. A pump rebuild or a pump swap and problem is gone. I have had mixed success with rebuilding the pumps, mostly better. New springs, balls and valve seats and pump will come up quickly.

A frozen unload valve doesnt usually care about warming up. And when you get them working, they usually stay working. But Hey,,, I could be wrong. Ask my wife.

Could be someone replace the metal ring with a oring or something even weirder.
f a fella is intent on determining whether the pump/pump relief valve will actually support building pressure, then he blocks off the inlet to the top cover by removing & reversing the accessory plate/cover and connecting a pressure gauge at pump or other port, starting & observing gauge.
 
Put in half a gallon of naphtha and a can of seafoam just for good measure. Fired her up and the lift picked up about twenty minutes later.(might be a fluke). I cycled it until my arm ached and then let it run another hour or so with it raised. Cycled it a few more times and shut it down. We'll see what happens in the morning. Still no spray or leakage that I can see looking in the filler hole.
 
Took about 4 minutes for the lift to pick up this morning so it's headed in the right direction. I'll do some more running and cycling and see what happens.
 

We sell tractor parts! We have the parts you need to repair your tractor - the right parts. Our low prices and years of research make us your best choice when you need parts. Shop Online Today.

Back
Top