The Oil Leak That Keeps on Leaking

The oil leak that just keeps on leaking

By Ron O’Neill / June 2009 Green Magazine


John Deere 420-430 rockshaft oil leaks:

  • where they leak
  • why they leak
  • what to do about them
  • replacement part numbers
  • the good doctor’s home remedies

Over a period of time, I’ve heard from a number of John Deere 420-430 owners who are frustrated with hydraulic oil leaks from the rockshaft areas of their tractors. You have asked me for some suggestions and/or what I do to repair them. During one of my more futile attempts to pacify a caller regarding this problem, I suggested that some oil leaks are just meant to be. Take, for instance, my old Harley; it always marks its spot for me with a couple of oil leaks on the garage floor. It’s kind of like the old bike signs its name under itself so that I always know that it belongs to me. But this way of thinking did not go far with the John Deere 420 owner; he found it to be only slightly amusing and returned with “Yeah, but this is MY JOHN DEERE, not an old Harley.”

Especially frustrating can be the effort to repair these leaks, only to realize a short time later that you did not stop the leaks, you only slowed them down. A 420U (utility) owner who lives not far from me sent his tractor through a John Deere dealership to have the rockshaft leak areas repaired. I spoke with him sometime later about it and his comment was “Well, they DID slow them down, but it still leaks.”

In some cases, many of you have sat at the John Deere parts counter and were not about to move your elbows until you had bought every seal and replacement part that John Deere had to finally repair that leak, only to once again learn that the leak slowed, but continued.

I have to admit that sometimes writing these articles regarding peoples’ personal concerns is like sticking your head up out of a foxhole in World War II—you know you’re going to get shot at; you just have to hope that you can dodge the bullet. At any rate, I have told you to stay tuned to your Green Magazine and somewhere down the road, I would do an article about this subject and try to explain it the best that I could and then let the bullets fly from there.

Sometimes one has to go a bit off track to get a problem solved. Maybe we can do that with this one. John Deere has solved some of its potential oil leak problems in the past in some rather unusual ways. Take, for instance—have you ever wondered on the John Deere 3020-4020 model tractors what that small plastic line is for that comes along the lower right side of the transmission?  If you follow it from end to end, it starts at the front pump seal cavity and ends by dumping back into the transmission case. It is a long, small plastic tube, sort of heading downhill from the pump to the transmission. Its purpose is to drain the seal cavity of its leak and just return it to the common sump of the transmission—sort of a “catch, retain and return the oil” theory.

The 420’s rockshaft assembly, as far as a working unit, is second to none in the way that it operates. Its lift capacity and position control sensing are above and beyond most small tractors of that similar size. On our small farm, we have a need to operate a two row, three-point corn planter. When the planter is fully loaded with seed and fertilizer, it is a heavy unit to lift and lower. We have tried using other brands of tractors, only to find that they can just barely lift the planter or it is too slow to lift it or the three-point arms needed to be longer to keep the rear wheels from hitting the planter when raised or the weight of the loaded planter totally lifted the tractor’s front end off the ground. The 420 passes all of these “tests” with flying colors with its hitch arms that can be extended. A beautiful tractor for the job—all except for one thing; the rockshaft leaks oil.

So here goes. ”Ole Doc” is sticking his head out of the foxhole, so start shooting! First, let’s talk about the easy stuff. Make sure your rockshaft vent (Picture 1) is not plugged with dirt.  This vent is located right on top of the rockshaft assembly and it is right under the tractor seat. Tractors that are working units are sure to collect dirt and build-up around the vent assembly. If the vent is plugged either from dirt build-up externally or from the vent itself, the rockshaft housing will build up an internal pressure and force oil out wherever it can—usually out the rockshaft ends.

I will try to pass along some reasons (as I see it) why the rockshaft seals are so prone to leak. First, one must understand that the rockshaft and integrated valve housing is the reservoir for the tractor’s hydraulic system. Let’s think of it as an open center hydraulic system with oil constantly flowing from the pump on the front of the engine to the back of the tractor’s rockshaft assembly and then back to the pump. The rest of the tractor’s transmission, rear end and final drives are sealed from it and carry their own “gear” oils and have their own fill levels. This means that the rockshaft housing is the hydraulic system’s oil reservoir and level source. I believe there are many slight variations of these rockshaft assemblies, but this unit’s level is at this point (Picture 2). I have come to realize that because of the tractor’s pump position (forward engine – camshaft driven) and 10 inches higher than the rockshaft assembly, that the system tends to overfill itself. This is because, as the tractor sits idle, hydraulic oil siphons down the hydraulic pressure and return lines from the front of the engine and ends up overfilling the rockshaft assembly.  If you look again at Picture 2, you will notice that the correct level is already at the bottom of the rockshafts. This means that at the current level, the rockshaft seals must hold back a constant oil level and not a splash situation. Now, add to this, as the system is not in use raises its own level, the chance of oil leakage increases. This is why the leak just seems to never stop and quite often, it seems to leak less when not in use.

In some other tractors’ rockshaft hitch assemblies, a level is maintained by an internal stand pipe, which bleeds off excess fluid to its common sump transmission below it. Its level is maintained BELOW the level of the rockshafts, making it much easier to keep from leaking. Because of the 420’s construction and oil reservoir heights, this idea cannot be utilized. So we must deal with rockshaft seals that are exposed to direct oil levels.

Now, regarding the seal problem—ZING. Here comes a bullet; I strongly suggest (as would many/most of the Green Magazine staff) that you purchase a parts book to understand and so that you can identify the seals for the 420’s rockshaft. John Deere parts catalogue (PC-505) will help you see what goes where and give you the seal part numbers and other needed items, not to mention avoiding long periods of time spent looking at your frustrated parts person asking you, “Well, is this what you mean?” I find that in many cases, a John Deere parts book is not only the answer for identifying parts and their numbers, but additionally is more helpful in disassembly and assembly than a repair manual.

Now, about the oil seals—or should I say “cork circles”? The oil seals on the end of the rock shafts are a cork ring, with a tin retainer holding it in place (Picture 3). The cork ring slips over the shafts and is held in place by a retainer ring. The problem here is that a cork ring is not a very good positive oil seal. Cork has a tendency to take a “set” and lose its compression on the shaft almost immediately. By now, all the tractors have some play or wear between the shaft and its support bushings. Any play in the shaft and its bushing pushes the cork ring out and guess what—leaky, leaky.

I have heard from some of you who have already gone the extra mile and bought and installed the bushings.  And even some of you with “deeper pockets” than mine have purchased new shafts and these I am told are not always available at any cost. Yet, still I am being told that success was limited.

Sometimes, as I have stated earlier, one must jump the tracks a little to get where you need to go. As of now, we have established the problem and that is why we were discussing replacement parts that do not seem to alleviate the leak. Here I feel we need to come up with a solution to the leak other than what we have already tried or have been offered as replacement seals.

Listen CLOSELY now. The old doctor’s potential fix is to use a 3/16 diameter o-ring in place of the cork ring (Picture 4). Using a 3/16 diameter o-ring with the O.D. and I.D. dimensions needed to fit the shafts tends to make a much better seal on the shaft than the cork ring. Keep in mind that the left hand side of the rockshaft has two diameter shafts—one for the outer lift arm shaft and one for the inner lift arm shaft.

Since these pictures were taken, I have added backup washers with the o-rings to allow more o-ring compression to the shaft when the original John Deere retainer is put over them. The reason this idea has worked where the cork rings have not is because the rubber o-ring has some amount of compression and retention to its original size and therefore keeps a much tighter seal on the shafts than did the cork rings. O-rings of this size and dimension and the backup rings can be purchased anywhere hydraulics are dealt with. Ironically, one of the 3/16 diameter o-rings used on one of the shafts is the same size o-ring I spoke of in a prior article, “Fear of the unknown,” regarding a power steering shaft leak on a JD 630.

As I have stated earlier, this is where my head is sticking out of the foxhole! I’m sure a bullet or two will fly my way, along with words something like “I’ve tried that and it didn’t work.” However, in my dealing with the problem, this is what I have found to be the answer and as of now, my old 420 is lifting the planter and not adding any hydraulic oil to the seed corn in the ground. However, research and development on the matter continues.  It would be the best fix if a lip oil seal that utilizes a compression spring could be purchased to fit the outer bore of the retainer ring and compress onto the shafts’ diameter. I am sure if such a seal could be purchased, it would alleviate the problem for good! The seal must be very thin in width, approximately one-quarter inch, to properly fit in the retainer rings’ cavities. Such seals cannot be purchased locally because of their dimensions. However don’t let your subscription to Green Magazine run out. The ol’ Tractor Doctor is coming very close to finding such a seal and quite likely a cure once and for all. Working with master catalogues from major seal manufacturers, it is very possible that seals as needed for this problem could be available. So stay tuned and read every page of Green Magazine. Updates regarding this article will be forthcoming.

Some of the information paid for and brought forward in this magazine is very valuable. For instance, have you tried the new NAPA 3039 paper sediment bowl filter for your old tractor (or any tractor for that matter)? I was introduced to this product in Green Magazine under “Product Review.” My hat goes off to whoever is responsible for the paper sediment bowl filter. Some of you out there who call me about inconsistent needle and seat leaks in your carburetor should have these filters in your tractor and on your shelf as I now do. They will stop a lot of gas related problems because of their finer filtration.

My wife, Jo Anne, and I believe that life is still good even with times as they are. We thank Green Magazine for letting us tell our stories. Oh, by the way, we have for sale a very nice oil catch pan. It fits nicely under the rear of a John Deere 420 rockshaft area; we won’t be needing it anymore.

Until we meet again—happy trails.

This column is written by Ron and Jo Anne O’Neill, who live at Oshkosh, Wisconsin.


We will have an update to this article next week, with some new information.