648G3 Hydraulic Cylinder

[CX3]

Hey guys Ive got a cylinder losing pressure on my 648JD.  Its on the grapple open/close.  When the detent is on it works good.  There are no leaks in the lines or cylinders.  The problem is when I have a jag of logs in the grapple and the detent is off, the grapple slowly opens up and the logs eventually fall out (at the buck pile.)  Do I need to tear the cylinders apart and re-pack them or is there something else to look at?  Also, is there any way to figure out which one is leaking off, or just rebuild both of them.  Thanks guys. 

[Autocar]

That would be my guess its bleeding past the seals and thats why you lose your load. Not much to resealing cylinders if you leave the cylinder part on the machine be sure to open the fitting at the bottom or your have a vaccum and it will be tuff to pull it apart and even harder to put back to gather. To bad we don't have time travel figured out I would pop over and help you  ;D

[1270d]

To check the packing;  ground the grapple or whatever the cylinder your working on. Make sure the rod is all the way in.  Take off the hose that would push the cylinder back out and cap the hose, leaving the fitting on the cylinder open. Now hit the close function.  If a bunch of oil comes out of the open port, the packings are bad. If nothing, your packing is still making a good seal.

[CX3]

Never thought of that 1270! Great idea thanks. 

Bill come on down and help Ill be working on it tomorrow morning lol

[kiko]

The seals in the rotator for the grapple could be leaking by as well.

[Autocar]

Kiko your have to send me your zip code number so I can program my time travel machine for in the morning  :D. The way my last couple of days have been going I would probably better off if I put my time into a time machine  ;D.Have a great week Bill

[CX3]

Can you explain why the rotator would have anything to do with the grapple arms leaking off?

[kiko]

I should have called it a rotate manifold. It allows continuous rotation of the grapple while still appling pressure to the grapple clys.  The two hose that go to the grapple through the yolk connect to the rotate manifold. the rotate manifold sits directly on top of the large rotate gear. take the two bolts on top of rotate manifold out, hoses from tractor side and the bolt for the hold arm and the outside piece of the manifold will pull right off. the seals are in the outside piece. If it is not leaking externally look for the middle seals to be damaged effectivly connecting the open and closed ports.

[kiko]

I would also try to resolve this issue as soon as possible what ever it may be.  with something bypassing the pump will stay on stroke and could lead to over heating of the oil and possibly a pump failure. Since the clys are leaking open there is a bypass even if it holds wood in detent. Autocar, if you get access to that time machine let me know there are many mistakes that I could change !! Dont let your children grow up to be diesel mechanics, they are never at home and when they are they are probally sleeping or complaining about back pain.

[CX3]

Ok I tried to takethe open/close cylinders apart. They would not come apart. I even pulled on them with a pickup. I figure if they held that good internally that the seals must be good. I will tear the manifold apart and look in there.

[kiko]

There are two types of grapple clys that came on the g3s. One has a nut on the outside and the other has a lock ring on the outside. They both can be difficult to disassemble . Can help with that if you can tell which type Cly it is.

[CX3]

It has a nut on the outside. The nut is roughly 1/2" thick with four maybe five square cut notches in it. After removing nut I slid the jug back and there is a snap ring. Thanks for the help

[kiko]

After removing the nut and pushing the gland in to expose the snap, remove the snap ring and the Cly should pull apart. But when it won't come apart I usually find that the retaining ring has pulled up an edge all the way around so the hole is to small to remove the rod gland piston assembly .  While the gland is down in the Cly barrel remove the rolled up edge with a debut bit and clean out any other corrosion on the barrel , lube it and the assembly will come on out.

[CX3]

I will try deburring it. Thanks