Backhoe JD #7 Backhoe - swing cylinder rebuilding - how to dismantle?

[techwrtr2]

Secure the fixed end, then use the rod/piston like a slide hammer to tap the gland out from the inside.

You could probably add some weight to the rod end to give the slide hammer effect more punch.

 

[Mechanos]

The swing circuit on the #7 is comprised of two single acting cylinders controlled by a double acting valve. This design gives the boom swing equal power and speed and in both directions. As mentioned above, the hole in the gland is a vent for the non-pressurized side of the single acting cylinder. There should never be anything but air on that side of the piston. Since you have hydrualic oil pouring out that vent, it means that your piston seals are shot. The bad thing about the design you have is that there is nothing to keep dirt, water and other crud from getting into the cylinder and once it's in, there is no way to get it out. The dirt and crud wreaks havoc on the piston seals when the cylinder is cylced and can also lead to scoring of the cylinder walls.

The other style of cylinder that has no hole in the gland, extra port, and short jumper hose from cylinder to cylinder allows the compressing air to vent into the other cylinder's expanding air space making it a closed system which keeps the dirt and crud out of the cylinders. It's a much better design.

 

[CasualObserver]

The other style of cylinder that has no hole in the gland, extra port, and short jumper hose from cylinder to cylinder allows the compressing air to vent into the other cylinder's expanding air space making it a closed system which keeps the dirt and crud out of the cylinders. It's a much better design.

Thanks for the clarification and that makes sense. That mixture of crud you describe is what coated me when I tried to loosen / remove the plate by pulling on the rod unsuccessfully today. Quite a nice mixture of dark gray / black ooze it was. Left penetrant sitting on the plate tonight hoping it might help loosen it if it is indeed only stuck on there as suggested earlier.

Unless someone tells me that plate is screwed in or otherwise retained, I am thinking about using a strap with a ratchet on it and slowly pulling the rod with that and see if it works out that way.

 

[Mechanos]

Be careful that the strap and/or the hook on the end of the strap doesn't take your head off if it breaks. Your best bet is the "slide hammer" approach. I've had to get quite aggressive with several cylinders get them apart.

Even if the strap doesn't break, it has the potential to store a lot of energy. If/when the gland does break free, the whole rod assembly will likely come out of the cylinder like a rocket.

 

[beenthere]

Unless someone tells me that plate is screwed in or otherwise retained

I think you will find it is not a "plate" but about an inch long bushing-like guide. Parts calls it out as a guide.

And I agree with mechanos, to not use a strap.

Maybe consider adding a port to the cylinders to connect a hose as shown in the pic. Might as well add new seals to both as the other one likely is in need, or soon will be in need of new seals.

 

[chriswheeler]

I'll start by saying I have a #8A, but the disassembly should be almost the same. Fully retract the cyl rod into the tube and chip all of the paint from the inside of the tube so the bushing can pass by. Mount the cyl in a vise, but don't grab it around the tube, it's thin and will bend and ruin the cyl. After the paint is remove, apply air pressure
( start @50 psi ) and work up until the piston blows the end cap loose, disassemble. These act as their own slide hammer and this doesn't mar any surfaces. Safety note *** Do not allow any one, or yourself to be in front of the cyl rod as the air is applied. Simple, quick, no hammers.
Chris

 

[CasualObserver]

Got it off and finished tonight. Used a small car jack with wood blocks between the cylinder and the rod pin. That worked it loose easily without issues, then used the piston method mentioned earlier to pull it apart. The nut on the rod came off quite easily. The OEM seal kit from John Deere had exactly the right seals for it inside. Not one extra seal in the bag. Nice thing about it was that the gland seals were tied together in the correct order and matched the original ones when I looked closely. Everything came apart and cleaned up nicely. Re-installed it without issued and appears to work properly and is leak free. I know what caused the leaks now. The bumper on the other side broke and allowed the swing cylinder to go further out then it should. It entered the area that is normally restricted by the bumper and hit the gunk and build up in the end of the cylinder that accumulated because of the vent port. I put a new pair of bumpers on it so that should not happen again.

Thanks for the advice, it helped a lot!

 

[beenthere]

:thumbsup: :thumbsup:

Glad to hear it.

 

[burnieman]

Did you find dirt in the cylinders? It's the low point in the system. I've replaced the seals in mine and the cylinders had a very fine abrasive in them which led me to change the oil in the whole system. The seals have lasted for awhile now.

 

[chriswheeler]

burnieman, I had the same crud in my 8A as well, and plenty of it, now that I think of it. Could sure see why the cups and seals failed. My 8A is a 1992, so guess I was lucky it went as far as it did. I sure can see how crud gets there over time, but any oil change won't do anything for what's trapped there. Guess if it lasts another 21 years it should outlast me this time.
Chris