Air in hydraulics?

AzChopp3r · Aug 11, 2013

Hi folks,

I have a John Deere 4300 with a 420 loader that I acquired a few months ago. I noticed something goin on with the loader for a few weeks now.

With the loader raised off the ground and bucket level, I can stand in front of the bucket and grab the cutting edge and lift the bucket and it will move about 3 inches. The slop is in the bucket cylinders. No leaks everything looks tight and right with exception to this slop.

So with the tractor running and bucket pointed down slightly, if I lower the loader arms, the bucket will straighten out to the point the slop is gone.

Sorry for not having a better explanation but I probably could post a video if needed.

My thinking is that there is an air bubble in the cylinders or the line and if so how do I go about getting it out?

adirondackmtnman · Aug 11, 2013

It should self-bleed. Do the arms/bucket hold their position if left up for an extended period of time?

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adirondackmtnman · Aug 11, 2013

Also...may be a dumb question, but have you checked the hydraulic oil level?

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AzChopp3r · Aug 11, 2013

adirondackmtnman said:
It should self-bleed. Do the arms/bucket hold their position if left up for an extended period of time?

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The main loader arms will stay in place but went and looked after an hour the bucket has drooped down.

As for checking hyd fluid, I have not done this and am not sure where to check it. I have an owners manual on order and still have not received. Would appreciate help on this.

Sysop · Aug 11, 2013

The only thing I'm aware you can do without special skills, tools, or taking things apart for further testing; is to cycle the hydraulics through their full range of motion four or five times which should bleed any air out of the cylinders. You may perhaps have a failure of a single piston, or perhaps aren't getting the proper pressures through the system. There are several causes that could create the circumstances you're describing and the only real option is a process of elimination going step by step through the system and test things. Some things would require special tools such as to test pressure on the hydraulic system, some things would just require disconnecting and testing such as unhooking the cylinders from the loader and cycling them. You could also check/change the hydraulic filters.

Let us know what you find!

adirondackmtnman · Aug 11, 2013

AzChopp3r said:
The main loader arms will stay in place but went and looked after an hour the bucket has drooped down.

As for checking hyd fluid, I have not done this and am not sure where to check it. I have an owners manual on order and still have not received. Would appreciate help on this.

The hydraulic reservoir on my 5045d has two sight glass windows to check hydraulic levels. The 4300 may be a different animal altogether, especially since it probably has hydostatic transmission. Look around for dipstick/windows around the back of the machine. Sounds to me like the tilt side of the loader valve may be leaking by, or the seal on the inside of the ram in the tilt cylinders may be leaking by if it droops and you're not losing fluid on the ground.

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AzChopp3r · Aug 11, 2013

Yes found the sight glass and with loader resting on the ground the glass is full. with loader raised and bucket dropped, the level in the glass drops slightly. No oil slicks on the ground at all. I have even parked the tractor inside the garage for a few days and the floor was clean. This tractor has only 470 hours on it which is low for a 2001.

So If I read correctly, pop the pins from the cylinders at the bucket connection and cycle them fully half a dozen times?

Sysop · Aug 11, 2013

Cycling them on or off the loader should bleed the air (as said by adirondackmtnman they are made to self bleed during operation), having them unhooked from the loader and cycling them would allow you to see any differences in the operation (i.e. one is hanging or not fully cycling causing extra work for the working one). Hopefully a REAL hydraulics guy can chime in and give ya some specific experiences that relate to your issues to give you some sorta direction to look in.

adirondackmtnman · Aug 11, 2013

Sysop said:
Hopefully a REAL hydraulics guy can chime in

Agree 100%...we can speculate all day, but someone who deals with it day in and day out would be able to pinpoint a lot better. Is this problem affecting the day to day use of the machine or just something you happened to notice?

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J_J · Aug 11, 2013

Install a 3000 psi hyd gage in a tee in the IN port of the first valve and you can see if the correct pressure is being developed.

If the cyl seals are bypassing, you probably can not activate the relief valve. That valve is a good indicator of hyd system health. If it can build up to the set pressure, then the hyd system is good.

If you have a suction leak, you will continue to suck in air and have the same problems.

Several people have already said the hyd system is self bleeding.

You could look in your tank for small bubbles if a sucking leak is happening.

A lot of hyd cavitation will also generate air.

banjodunn · Aug 12, 2013

G'day it sounds to me like you have got a bucket cyl seal leaking ( piston seal ) . If you have te loader up and cycle the rams though their stroke 3-4 times and then get off and try to move the bucket does it feel firm? If it is then if you leave it for half an hour or so and try to move it again then your seals or spool is bypassing.

Best way to check the cyl's is to rest the loader on the ground and remove the cyl hoses at the cyl and apply air press to the top side of the cyl i.e you are trying to extend the cyl and look for oil/air coming out the bottom fitting. I usually put a hose on the bottom fitting and run it into a bucket just in case the oil sprays out if it does then your seals are shot and need replacing.

Jon

AzChopp3r · Aug 12, 2013

Thanks banjo I will do this test in the next few days and let everyone know the results here. As for a sucking leak or cavitation, the problem exists only with the bucket cylinders and I am also not able to look into a separate hyd oil tank as I do not have one.

J_J · Aug 12, 2013

If you can't see in the tank for air bubbles, then remove a bucket hose and place in a bucket and look for small air bubbles.

Run the tractor for 5 min and work the bucket you do this test.

Maxwelshouse1 · Aug 12, 2013

When you check the hydraulic fluid make sure the loader frame is on the ground that all hydraulic cylinders are retracted (all hydraulic rods are in). Otherwise you could add too much oil. Once you are confident of oil levels, you can cycle the system several times, and go on from there... Mans temptation is to think the worst case scenario. But slow down, drink a cup of coffee and think "simple." Life gets too complicated anyways...Why make it more difficult! Lol! Good luck!

AzChopp3r · Aug 16, 2013

Ok today I was able to get to the tractor and do a couple tests.

Again, with the loader arms raised about 3 foot off the deck and bucket level, I can grab the cutting edge and lift while and see the bucket cyls retract about 2 in travel.

I then cycle the bucket 4 - 5 times fully.

Go back to the bucket and lift and it is solid. But I can tell it is sagging and at a rate of 1/2" cyl travel per min.

After a minute I can lift on the bucket and slop is already beginning to appear.

So I disconnect both cyls from the bucket and cycle them. I notice that the left cylinder is lagging considerably as compared to the right.

Thiese were the tests that I was able to perform today. Any suggestions?

J_J · Aug 16, 2013

Can you swap hoses on the valve from the lift cyls to the tilt cyls.

If the problem does not shift, then it is your seals on one or both cyl.

Ilikeurtractor · Aug 31, 2013

Can someone explain to me how the loader hydraulics "self-bleed" as referenced in this thread earlier? I'm installing a loader on a tractor now and this bleeding issue is puzzling me. I not at the point to operate the loader but am to the point where if I need to bleed it I should do it now before tightening up all the lines. It seems to me the air will stay in the lines from the control valves to each side of the piston in the cylinder unless the air is let out at the high points on each side of the piston while applying hydraulic fluid. Unfortantely, there are no bleeds at the high points, only at the connections (which are not at the high points). I'd feel better knowing how this self-bleeding works once past the control valve for the loader. Should I try to get as much air out as I can going to each ram on either side of the piston, or just hook everything up and not worry about it? I'd rather not have a "springy" loader when I'm done. Thanks in advance.

Sysop · Aug 31, 2013

"self-bleeding" just means there's nothing you need to do to do it except cycle the hydraulics throughout their full range of motion a few times. Once you start the tractor and the pump is flowing, it will push the fluid in and air out, you just need to cycle everything to ensure no air is stuck anywhere. Air being 'hidden' somewhere in the system could end up in the wrong place at the wrong time and cause a load to jerk or bounce and cause bad things to occur...

Ilikeurtractor · Aug 31, 2013

Thanks for the reply. I'm struggling with this scenario though (bare with me):

Say we have a vertical, double-acting cylinder and the piston is on the bottom (ram retracted) and we want to extend it and there is nothing but air between the control valve and the piston in the cylinder. When fluid is applied the air in the line will go into the cylinder under the piston, compress to some extent depending on load, and extend the ram. When we retract the ram from this position we apply fluid to the top of the piston in the cylinder and it pushes the fluid out first below the piston (since it is heavier than air) and the air remains in the line (or under the piston). I'm curious as to how the air gets out in this case. Unless the air leaks by the piston and gets into the top chamber where I can see then how it would be expelled out of the system upon cycling. Maybe that's how it works. I suppose air will leak by the piston more readily than fluid.