Green Tractor Talk banner

JD400 Steering Yoke Compartment Drain

1159 Views 7 Replies 2 Participants Last post by  Chilliwack Murray
I'm hoping someone who worked on these machines remembers where the drain for the Steering Yoke compartment is. The manual describes leakage from the open center power steering allowed to leak down into this chamber to provide lubrication and overflow returning to the transmission case.

I resealed the steering column a year or two ago and everything was good for about 50 hours but now I find this chamber is being pressurized and blowing the seal out particularly on a right turn. I've pulled the steering column apart and don't see any issue though I will replace the seals again. I believe the source of the oil was the return line port on the right cover - I didn't have a gasket and used silicone which I believe failed where the return flow passes from the transmission case to the cover allowing return oil into the yoke chamber.

I want to ensure the overflow return to the transmission case is not obstructed but I cannot locate it with a mirror and flashlight, pick, mechanics wire or my hands. There is a drain passage from the bottom of the yoke chamber to the right side where there is an external plug but that appears to be just for draining the chamber as I cannot see or feel any other opening in that drilling.

I'm hoping someone like TX Jim will remember where this overflow drain is in the case. I'm concerned that the silicone that blew out may also have blocked the overflow and even with the proper gasket sealing the return passage the intended leakage will eventually overfill the chamber.

"A small amount of this return oil enters the
center cavity of the valve housing through an
orifice in return passage to lubricate the steering
wheel shaft threads and thrust bearings. This
oil at no pressure is allowed to seep downward
through the center of the steering piston rod to
the steering yoke compartment in the clutch
housing. Overflow from this compartment returns
to the transmission case." Font Automotive design Art Engineering Circle

1 - 8 of 8 Posts
See hole(red arrow).
Steering drains to transmission case through this hole.

Got to this quicker than I expected. It looks like arrow in your photo would be the underside of the Yoke Compartment but that case doesn't appear identical to the one in the parts drawing (which matches what I have). I'm guessing the drain should be near the bottom of the Yoke Compartment maybe in the drilling to the outside drain plug pictured here below.

Can anyone confirm this or have a picture of the top side of that housing that shows the inlet of the drain? In the mean time I will root around some more and try to find a drain hole.


I’ve spent an hour last night and again today with a mirror, pick and my hands and I can’t find a drain to the transmission case anywhere in this cavity.

The only place I can’t be 100% certain is the drilling to the drain plug but I’ve run a pick over the length and looked from both ends with a mirror and light.

The photo of the green housing doesn’t appear quite the same as the drawing, possibly because this is a reverser housing? I can’t believe it’s possible to have no drain of any kind where there is always the possibility (and intent) of some leakage in.
So it's all inspected and re-assembled with all passages clear and open but I still get pressure building in the yoke compartment. There is clearly flow into this area - about 10oz per minute I would estimate but since it is building pressure the drain where ever it is must be plugged.

At this point I'm considering drilling a new drain through to the transmission case as my only other option if I can't find the drain to clear it.
Could it be that the return oil to that area is receiving more volume than the drain hole can actually displace?

It's been many years since I've worked on a JD400, so I have a question.
There's a fitting that attaches to this passage(see threaded hole in image below).
Where does the line, that connects to this fitting, come from?

That was my initial thought. I pulled the steering column apart again and verified everything is clear and assembled right. My other suspicion for too much flow was that this port which comes from the main casting had blown out the silicone and was dumping into the compartment overwhelming the drain.

That line tees into the steering pump supply fed by the transmission pump so it normally has pressure with the machine running.

It seems like the drain (overflow) is completely blocked - if I run the machine for 15 seconds and cycle the steering with the drain plug loose, shut it off then tighten the plug it is still holding pressure in that compartment when I open it a minute later.

There must be a drain running roughly where the arrow shows that I can’t see. I guess the next step is to pull the shifter cover and look for a drain on that side. If I can’t find it, I might just drill a new one from that side under the reverser shaft.

Automotive tire Motor vehicle Amber Asphalt Wood

It’s likely the original culprit was the silicone both allowing extra leakage from the return and eventually blocking the overflow path. The circled hole is the return to the transmission case and it was mostly blocked with silicone.

When I reinstalled the steering column with my home made gasket I cut out the holes I saw but didn’t clue in to the fact one has no matching hole on the steering column. That sealed the housing completely and blew the seal out with some force.

Fixture Yellow Motor vehicle Gas Automotive exterior

Now I see that the oil fills the yoke compartment to the top then flows through the gap left by the thickness of the gasket between the two housings to the low pressure transmission return passage. The original gasket covers only the edges and around the high pressure return port. Once I removed the material around the transmission overflow passage it works as it should.

Motor vehicle Font Automotive exterior Gas Auto part

Thanks for the suggestions!
1 - 8 of 8 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.