Rebuilding a JD 420 Loader Lift Cylinder

WarrenM · May 31, 2022

Hi all,

I have a John Deere 855 tractor with a 420 FEL.
One of the lift cylinders has developed a leak.
I tried replacing the seals but no success.

There are a few youTubes on this which are helpful but lack detail.

Can anyone point me to a shop manual, or other reference, that covers this topic?

Any advice greatly appreciated.

Warren

Roadworthy · May 31, 2022

Have you considered checking in with a local hydraulic shop? They can rebuild the cylinder, probably for less than you'd expect, and point out any defects which may be causing your leak along the way. If it's one of a pair of cylinders working together you may wish to consider having the other done at the same time rather than having it fail soon after the rebuild.

WarrenM · Jun 1, 2022

Yea, that's my "plan B". But I'd like to do the work myself if possible. Still on the hunt for a good reference.

erikjohn67 · Jun 1, 2022

I did the ones on my 790 loader 70 about six months ago. I watched as many you tube videos as I could find and then did all 4 cylinders on mine even though only 1 was leaking.

There are a couple tricks if I remember right and the kits I had came with some different glands depending in the exact application. I bought genuine JD seals.

It is easy to install one of the seals backwards if you aren’t looking at it right and I needed to use boiling water on the one of the o rings to make it elastic so I could get it installed properly.

Do you have any idea what you might be doing wrong?

WarrenM · Jun 1, 2022

Two of the o-rings in the kit look identical, but have different part numbers. The kit has no indication as to which-is-which and on my first attempt I couldn't get the gland seal assembly back in the cylinder. I swapped these two o-rings and it went back together. I may have just man-handled the rings a bit too much.

erikjohn67 · Jun 3, 2022

The seal that goes inside the gland before the oil seal that you press fit in is the high pressure. Its a bear to get in correctly and helps to drop in boiling water for a minute then bend it into a u shape (think of a sling where it doubled up) so that you can fit it into the hole of the gland and get half of it into the groove. Then you need a metal pick or small flat screwdriver to get the folded piece unfolded into the top part of the groove. Just have to be careful not to chew it up while you do this but it is pretty a pretty tough seal. Tougher than you would think.

All the other seals are pretty easy to install you just need to pay close attention when you take one apart (take pictures of one that you haven’t opened yet)so that you have the lips and grooves in the various seals in the correct orientation/direction as they were from the factory.

Between using the diagram that comes in the instruction and your pictures you should be able to understand how to orientate everything when your reinstall the new.

dfkrug · Jun 3, 2022

The seals inside the gland for the 420 FEL cylinders are about the most difficult to install, due to the tiny 25mm rod diameter. I have done several of these. Before I went out and bought the right tool for the job (photo).

Before I bought some gland seal-bending tools, I used to take three rods to forma a U-bend in the the seal while heating it in hot water. Not easy!

You could also make this tool.

WarrenM · Jun 4, 2022

erikjohn67 said:
The seal that goes inside the gland before the oil seal that you press fit in is the high pressure. Its a bear to get in correctly and helps toeal drop in boiling water for a minute then bend it into a u shape (think of a sling where it doubled up) so that you can fit it into the hole of the gland and get half of it into the groove. Then you need a metal pick or small flat screwdriver to get the folded piece unfolded into the top part of the groove. Just have to be careful not to chew it up while you do this but it is pretty a pretty tough seal. Tougher than you would think.

All the other seals are pretty easy to install you just need to pay close attention when you take one apart (take pictures of one that you haven’t opened yet)so that you have the lips and grooves in the various seals in the correct orientation/direction as they were from the factory.

Between using the diagram that comes in the instruction and your pictures you should be able to understand how to orientate everything when your reinstall the new.

The problem is that the seal kit came with no instructions or diagrams. I made a pencil drawing of the old seals as installed. All I have to go on is that drawing and the exploded line drawing in the JD parts catalog.

WarrenM · Jun 4, 2022

dfkrug said:
The seals inside the gland for the 420 FEL cylinders are about the most difficult to install, due to the tiny 25mm rod diameter. I have done several of these. Before I went out and bought the right tool for the job (photo).

Before I bought some gland seal-bending tools, I used to take three rods to forma a U-bend in the the seal while heating it in hot water. Not easy!

You could also make this tool.

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