JD450B Oil Foaming in hydraulic tank

[lsgadd]

I have a JD450B that's is showing foam in the hydraulic tank sight glass while running regardless if I'm using the bucket or if the machine is just sitting still running,
Now here's the strange part, if I'm at idle to half throttle the oil does not foam, but above half throttle the oil foams.
I've noticed the pressure line coming out of the pump has a slight vibration when above half throttle to full throttle also it seems like I hear the pump cavitating faintly, but I'm not 100 percent sure as the sound is very low.
When I shut the tractor off within 10 to 15 min the oil in the tanks sight glass becomes clear with no foam so that tell me there's no water in the oil.

I've changed the complete loader valve assembly, pump, filter in tank, suction line rubber hose with no change in foaming.
There's no oil leaks that I can find as I have the belly pan and the front housing and grille assembly off the tractor.

the boom and bucket seems to still works fine even with the foam in tank.

Any Ideas ?

Thanks,
Scott

[LeonardL]

So my first question is how bad is this foaming? You will get a little bit of foam just from the return oil as it returns to the tank. My first thought is the oil itself. Did you replace the hydraulic fluid? The wrong fluid can cause foaming so I would make sure you used the right fluid. You need either a straight hydraulic fluid or Universal Tractor Fluid. Deere's fluid is branded as "HI-GARD" but any good TH fluid is oaky as long as it meets Deere's specs.

If you were getting cavitation from it pulling in air then you should have a leak when the machine is off or not running. If you have internal cavitation then you have a restriction in the feed or suction line to the pump. So make sure that line is large enough first of all and has no restrictions like a kink or a fitting that wasn't installed correctly. You should also check the tank and make sure nothing has gotten over the suction port that feeds the oil out to the pump.

I would also make sure the filter in the tank is seated properly. If it is loose then it will have a foaming effect on the oil. As I recall, Deere filters the oil as it returns to the tank and not the suction side as it feeds the pump. So if that filter is loose then it could be foaming the oil because of it.

I hope this helps and keep us posted on what you find.

[lsgadd]

So my first question is how bad is this foaming?

It's not solid white foam, But there's a lot of very small white bubbles.

Did you replace the hydraulic fluid?

Yes, I've tried 3 different types of fluid, Hy-guard, tractor supply's 303 fluid and Oreilly's premium hydraulic fluid.

If you have internal cavitation then you have a restriction in the feed or suction line to the pump. So make sure that line is large enough first of all and has no restrictions like a kink

I have the OEM suction line off a JD450B at the moment on the tractor, But I have tried the suction line from a JD450 as they are a little different, but it will work, But it didn't make any difference in the foaming with either of the suction lines.

You should also check the tank and make sure nothing has gotten over the suction port that feeds the oil out to the pump.
I would also make sure the filter in the tank is seated properly.

I have had the the top off the tank several different times,I've cleaned the inside of the tank, I've even tried to leave both the pumps suction wire mesh screen and the control valve return filter off just to check it, But it didn't make any difference in the foam.

The only thing I see different from my other 450's is the bypass in the tank stays raised on this 450B while the oil is cold but it doesn't raise once the oil get warm were as on my other 450s I've never seen it raised on them.

I have literally tried every thing i can think of with the same outcome.
i am beginning to think my 35 plus years of being a mechanic is being reduced to becoming a parts changer by this tractor

[LeonardL]

It looks like you have done all the right things. There will be a given amount of air or small bubbles in the fluid as you work the machine. If it is just that, as in residual bubbling of the oil then I wouldn't worry about it. It's just the nature of things on heavy equipment.

The bypass you mentioned is curious but I have never seen one of those fail. Not saying it isn't possible because anything is possible and there is always a first time.

The newer 450s work with a given amount of pressure that will build up inside the tank as the machine comes up to temperature. They are a closed system. I don't recall on the older 450s if they were a sealed system or if they were vented. If it is a vented system then it could be pulling a vacuum if the vent is stopped up. That will cause cavitation and foaming. Have you tried running it with the cap loose?

You could also try to isolate the system by using an external tank and then you can test the system. See what it does while working from an independent tank. All you need is a tank with a feed line and a return.

So... I would check for a vent and make sure it is open. If there is no vent then I would assume it is a closed system. If it is a closed system then look at the cap to make sure it is sealing correctly. I would also look at that bypass to make sure it is functioning as it should. You also mentioned replacing the control valve. Make sure you don't have a bypass or a restriction in that new valve. That will cause foaming but should also cause excessive heat. These machines run warm on the hydraulics but if there is a restriction then they will be hot.

You mentioned being a 35 year mechanic and that you're getting a bit frustrated. Hang in there and don't give up. I've been bending wrenches for as long as I can remember. So I'm 70 now and I started when I was just kid and have been around equipment all my life. And yes... a lot of that time had its share of frustrations. I had a New Holland TS 110 that just about bested me! I developed a devout hate for that tractor and would have gladly given it to some other sucker to figure out. It took me over a month to find a tiny little o-ring buried in the depths of the transmission that was causing the entire issue.

Your issue will be simple once you find it. Just remember that hydraulics is all flow and control of that flow. Follow the system and look at each component.

[KSS Const.]

I had a similar problem with my 450C after I bought it. I replaced hoses, rebuilt cylinders, etc.. and assumed it was air in the system. Turned out to be a leaking blow off valve on the 9300 backhoe tank that was almost imperceptible. I didn't find it until I dismounted the backhoe to work without the weight on the back. Just a drip that didn't require adding fluid, but once I fixed it, the problem was solved. Drove me nuts for a couple of months. I guess because of the location it would drip very little while under pressure. After shut down the fluid cooled and contracted it drew air into the system. If you can't find a leak it's probably in a high point of the system.

[lsgadd]

Well I finally found the problem, I removed the power beyond fitting that's on the control valve and replaced it with a plug and the foaming in the tank stopped, I assumed the 2 o-rings on the power beyond fitting are leaking internally in the control valve, but i haven't tried new o-rings on the fitting yet as i have the correct size ordered.

[LeonardL]

Cool!! Glad you got it sorted out. Now you can stop pulling your hair out!!