Air in hydraulics?

[EddieWalker]

I think people confuse the brakes on their car or truck with the hydraulic system on a tractor. In a car, there is nowhere for the fluid to go, so if there is air in the lines, it remains there and you have mushy brakes until you get rid of the air by bleeding the lines. On a tractor, the hydraulic fluid travels around the system, through filters and into the storage tank. This movement of the fluid through the lines forces any air that might be in the lines, out of the lines. If the tank if full, any air that was in there goes to the tank, but since the intake line from the tank is below the level of the fluid, no air can come back into the line.

As for the Original Posters question, his seals are worn on his cylinders. Probably both since it's so loose he can move it with his hands. Deere should have a replacement kit that you can do it yourself. On my larger cylinders, I just have a guy who specializes in cylinder rebuilds do it for me for a hundred bucks plus materials. I just take off the cylinder and bring it to his shop.

It will only get worse, and you have to replace the seals. If you wait too long, some damage to the cylinder wall may occur, but that's pretty rare.

Eddie

 

[AzChopp3r]

FYI, I have basically decided that rebuilding the seals in both bucket cyls is the best option. Although I have seen online that these JD cylinders are somewhat notorious for bypassing. Some have even gone to the extent of replacing the cylinders with aftermarket ones. I have watched videos on rebuilding these cylinders and appears pretty straight forward however if anyone here has any more on this it would be appreciated.

 

[SSdoxie]

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.

The air mixes with the oil so it is carried in the oil back to the reservoir where it separates and air goes out the vent. When the cylinders reach the end of stroke, hold lever a couple seconds so relief opens to make sure oil is fully pressurized thus mixing with as much air as possible each time.

 

[Ilikeurtractor]

I'm glad it works out that way because complete bleeding of the air manually would be a real PITA. I got the loader piped up today and as described, the air appears to have purged itself out through operation. Thanks for the explanations.