Need advice with a leak on JD490D excavator

I have a 1987 ish JD490D that was converted into a Fabtek harvester sometime in the 90's. I have hydraulic oil that is leaking from underneath in the center of the machine. The oil is coming out at the main ring gear that the center is on. Reading through my book and looking on line my assumption is this may be coming from the rotary manifold somehow, my second guess was seal around the output shaft at the bottom of the swing motor could be leaking? Looking from the top of the swing motor I can not see any oil on the deck plate. Any thoughts on this? Can the rotary manifold come out from the bottom after removing the large circular cover?

There should be a dipstick on the swing rotation gearbox. If oil shows proper level on dipstick, problem isn't with the rotation box. If oil doesn't show on dipstick, top it up to proper level, then operate machine to see if oil disappears from dipstick. I'm near certain there is a fill plug port on opposite side of dipstick location, remove plug and dipstick, add oil to fill plug hole, keep checking with dipstick until you achieve proper level. If oil remains in the rotation gearbox your problem is likely the center rotating joint.

willie59 said:

There should be a dipstick on the swing rotation gearbox. If oil shows proper level on dipstick, problem isn't with the rotation box. If oil doesn't show on dipstick, top it up to proper level, then operate machine to see if oil disappears from dipstick. I'm near certain there is a fill plug port on opposite side of dipstick location, remove plug and dipstick, add oil to fill plug hole, keep checking with dipstick until you achieve proper level. If oil remains in the rotation gearbox your problem is likely the center rotating joint.

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Thanks Willie, I know the port you are talking about, but that is gear oil, and it is hydraulic oil that is leaking. What do you mean by the "Center rotating joint"?

If the swing gear box isn't over full, then the swing motor output shaft isn't leaking. When the swing motor output shaft leaks, the hydraulic oil will overfill the gearbox. If the swivel is leaking, you should be able to ID the source upon closer examination, by stalling the tracks with a large piece of round bar.

The rotator, the swivel, the center swivel, the rotating joint, any number of names. It's the manifold in the exact center of the rotating structure, it delivers oil to the lower frame.

Ok, the gearbox is not overfull, however the area that the gear and bearing are in is full of hydraulic oil. There is an access cover under the main boom pins I removed and checked to be sure, and yes its full of oil. From under the machine when looking up at the center manifold there are two pipe plugs, one larger and one smaller on either side of the manifold. The oil leak I found on the outside of the machine is coming from around where the main ring bolts hold the center of the machine together, so it is the oil that I was looking at under the cover. Am I right in presuming the center manifold is leaking into this area? From under the machine it is pretty clear how to disconnect the drive lines and drop it down and I see the hoses on top - is this how it comes out? I included a photo of the access cover I am talking about. ThanksView attachment 112726View attachment 112727

Caught you on DP.
On a Cat (never did a Deere), all lines are removed from top and bottom, top dust boot retaining ring is removed from chassis (boot can remain on swivel via it's hose clamp), then mounting bolts are removed from the underside, and unit is lifted out.

And I'll add this about removing a center swivel, take out your phone and snap a pic of how it's oriented, top and bottom. Also put some form of mark on it before you remove so you don't re-install it backwards or something. Don't forget to relieve the pressure on the hydraulic reservoir. Mark each hose/pipe connection with a center punch, one dot on a hose/fitting, two dots on the next hose/fitting, three dots on the next, etc. And lastly, have proper plugs/caps for disconnected hoses/pipes to minimize oil loss.

you'll want to use a hoist. it's too heavy to catch by hand when you drop it (about 50 lbs).
a seal kit should be about $150. if the seal races are too pitted you'll have replace the whole joint which is pricey.

you'll want to use a hoist. it's too heavy to catch by hand when you drop it (about 50 lbs).
a seal kit should be about $150. if the seal races are too pitted you'll have replace the whole joint which is pricey.