FEL bucket goes spongy after warming up

[OldTrix]

I have a Mahindra 2665 that I bought with about 250 hrs on it. I notice that when cold, just after starting, the bucket curl is firm, as in I can drop the bucket down and then lower the loader and lift the ft end of the tractor off the ground. A while later, when warm, I can tilt the bucket down and lower the loader and the bucket just curls up instead of holding firm like it did when cold. It does stop and hold, but only after it curls up about a foot or so. I can apply more force to the bucket to uncurl it again, but I'm puzzled why this occurs. Usually, hydraulics will hold a given position unless the force is such that the relief valve gives way.

I've done the usual full travel/hold bleeding techniques to both loader and bucket, but that doesn't change anything. Cracking the lines open at the cylinders did not show signs of any air escaping, and I see no obvious leaks or any issues with the hydraulic lines.

Any thoughts on likely causes?

 

[OldTrix]

I will add, there does seem to be something off with the loader joystick. The uncurl function isn't as linear as the others. It seems to have two speeds based on the joystick position. All the way over is slower than 3/4 the way over. it behaves as expected until you pull it hard right. Maybe the cables need adjustment?

 

[oldnslo]

That model may have the regenerative dump option which speeds up the dump by 30 - 40%.

Soft or spongy normally indicates that air is getting into the system but I would expect this to more of a problem when oil is cold vs hot. Any rubber hoses on the inlet or suction side of the pump? If yes check any clamps or fittings to verify they are tight and inspect the hose for age cracks and squeeze to see if feels soft and spongy. Should be rigid and difficult to squeeze.

Do you hear any sound changes on the pump or system when working with cold oil vs warm or hot oil?

 

[OldTrix]

No real changes. If it's really cold, like in winter, the pump will be a bit whiney at first, but nothing too unusual. Nothing different on summer days. The hoses all check out. The pump routes to the loader valve via typical hyd hose, with PB headed back to the rear remotes. 3rd function hoses are also fine and routed correctly. It does act like air gets in there somehow, yet the next morning its solid as a rock again.

 

[oldnslo]

Off the wall thought but can you check the temperature of the pressure line to the loader valve vs power beyond and tank. If, repeat if there is some type of restriction in the flow path it might aerate the oil over time which would then settle out overnight. Checking for heat rise in those lines might show you if the power beyond or tank line gets hot quicker than the inlet. Again off the wall but gotta start somewhere.

Does 3 point lift a load same as always? If it also gets soft with hot oil that would kind of support oil getting aerated.

 

[OldTrix]

I'll play with that later today- I've switched to the grapple for rock collecting, but can at least give it the feel test for temp.

TPH has never been a problem, always lifts, never sags.

 

[Mike1955]

Another opinion, sounds like the cylinder leaking through. It is worse when warm. Just what I’ve run into on my stuff

 

[OldTrix]

I would think a cylinder leak would be a slow release. This acts like an air bubble, it gives a certain distance then, stops hard. Unless a certain section of the cylinder is damaged?

 

[Mike1955]

Well you might be right. This was a single action cylinder I just replaced. I replaced it, was only 2 hundred something, instead of packing. Faster can get back to work.

 

[OldTrix]

No real difference in temp that I can feel. My Backhoe runs off the rear remotes, and it seems to work OK, too. WHen i have the remote valve switched on to run it, I can hear the fluid running through it, sort of a hissing sound.

I'm beginning to wonder about the whole loader at this point. Running the grapple, I notice even the loader arms have give in them. Try to press down around a rock, and if it slides off, the loader drops a couple feet. It also lifts unevenly at times, twisting the whole loader frame.

I also notice the third function doesn't hold pressure. Grabbed a rock, curled it under (the top jaw is much longer than the bottom on my grapple) to hold it, and I could see the jaw slowly opening up. Had to hit the button every 5-10 secs to keep it clamped tight.

It really acts like there's a lot of air in this thing, but running it full travel each way, It seems to cycle ok.

Would a flaky pressure relief valve do this? I do have a gauge I can pop in line to measure pressure.

 

[oldnslo]

Lifting crooked would point towards potential of one of the lift cylinders leaking internally but that shouldn’t cause any sponginess and would expect that to a constant problem not only when cold.

 

[rScotty]

No real changes. If it's really cold, like in winter, the pump will be a bit whiney at first, but nothing too unusual. Nothing different on summer days. The hoses all check out. The pump routes to the loader valve via typical hyd hose, with PB headed back to the rear remotes. 3rd function hoses are also fine and routed correctly. It does act like air gets in there somehow, yet the next morning its solid as a rock again.

You say it works good when cold, but not when hot. I can't think of any reason that temperature would cause such a problem. But a suction air leak certainly would. Instead of temperature as a cause, we are looking at the time the tractor is running...same thing. The amount of entrained air would increase as the tractor warms up. Then the hydraulic fluid would give up the air overnight as it cooled.

Hoses aren't the only places that can cause a suction leak. Connections are known to be a problem, and the hydraulic pump itself can pull air past its seals. It seems to me that all your symptoms point to a suction air leak somewhere. First thing would be to check the fluid for air.

Simply take a sample of the hydraulic fluid after it warms up and the problem begins...maybe use a syringe or turkey baster to pull a sample of fluid from the sump and put it in a glass jar with a loose lid. Entrained air makes the fluid yellow and opaque, but it clears up after sitting overnight.

Another way that is more work..... but you could put a section of clear tubing into the FEL return line. Then you could see the fluid in real time. Might want to check the return line pressure with your gauge first, & maybe put the clear section closer to where the return line enters the sump...just in case it leaks. But that's your call. Hardware store clear vinyl or polyethylene tubing will handle 50 psi easy. Barbed fittings with worm drive hose clamps will too.

rScotty

 

[Mike1955]

Oil trim I don’t think a relief valve would cause that effect. That machine definitely has a lot of wear in the cylinders and the bushings and the control valves And the oil has possibly lost some of its viscosity. Add it all up and you get a little instability.

 

[OldTrix]

I know the grapple is solid as it's only 2 yrs old and was fine on my old tractor. The slow bleed down of the grapple jaws points to a leaky 3rd function valve in my mind.

I had the loader off the tractor last week and looked at all the couplers and fittings. Nothing appears to be leaking externally, so I think the coupler o-rings are OK.

I'll chase the suction lines next and see what I can find. I'll also pull the strainer to ensure it's not plugged up.

 

[rScotty]

I know the grapple is solid as it's only 2 yrs old and was fine on my old tractor. The slow bleed down of the grapple jaws points to a leaky 3rd function valve in my mind.

I had the loader off the tractor last week and looked at all the couplers and fittings. Nothing appears to be leaking externally, so I think the coupler o-rings are OK.

I'll chase the suction lines next and see what I can find. I'll also pull the strainer to ensure it's not plugged up.

It's easy to tell if you have a suction air leak. Cold hydraulic fluid that has set overnight is clear.

If you pull a sample of oil from the sump when it is hot and you see that the fluid is still clear like it was when the fluid was cold then the tractor doesn't have a suction air leak problem.

But if the hydraulic fluid has air entrained in it the fluid will look cloudy like this photo. Fluid that looks like that is filled with microbubbles of air and will cause the cylinders to be "spongy".

 

[OldTrix]

Well, I think I may have identified a potential source. I've been out all day, moving some deadwood, rocks, etc. with both the grapple and the backhoe. Figured I'd take a shot at a stump I want gone just to chew up an hour or so. Tractor has been running fine all day. Set up and start digging. I usually set the engine around 1100-1200 RPM for backhoe work, which seems to do the trick.

After about 15 min, I turn around and notice black smoke Uh-oh. Thinking it may be loading up, I rev it a bit, it doesn't clear. Black smoke turns to white, and the next thing I know it's on a runaway! Stall it, and ponder what's going on. First thing I do is check the dipstick. I had changed the oil 15 hrs ago, and check it every couple of days, and it was fine yesterday. The level on the stick is completely full. I think the pump is leaking into the crankcase somehow, which would explain some of the hydraulic problems I've been having.

Thoughts? Where else could the motor suck in hydro fluid? It's a gear model, so it could be worse. Hopefully the motor isn't toast. After it cools, I'll drain and refill the oil and see if I can move it.

 

[OldTrix]

A new hydraulic pump seems to have solved the issue. No more weird noises from the steering and the hydraulics have found new strength. It's a tandem pump, one side for power steering and the other for general hydraulics. Beside the front seal leaking like a sieve, I think one side of the pump may have been stealing from the other. Sourced the pump from India at about half what Mahindra wants for it. Better yet, I beat the tariffs that kick in this week.