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JD318 suddenly will only move slowly

1576 Views 13 Replies 7 Participants Last post by  TUDOR
Assume nothing about my JD318 knowledge in this thread. I have pulled the engine on one twice to fix starter problems, so i understand the whole drive shaft hydro spline linkage design.
I have two JD318's, one with a blown engine and leaking hydro that has been on the backburner for a long time. I have a new engine for it ... just no time to fix it up.
The second one was purchased from a guy for $600 a few years ago, and he used it primarily for snow plowing. Not blowing, he had the plow.
I've been running this one for about six years, roughly, and I've had to correct "modifications" the guy made ... bottomline, it has run OK, but I'd believe anything about it not being stock.
P218 engine, and the only problem it has is a little wonky starter that picks up after two or three key turns.
Almost the entire time I've had it, the hydro has been jerky, and I've just lived with it. I figured it was just the linkage being sloppy and never had time to pull the seat and pan and work it.
Last weekend, I added some hydro oil because the sight glass was not showing oil, and after a pretty hard day of mowing some tall grass, it started acting strange - it would not move at all when I moved the control lever initially, and when I'd get the lever to about half forward, it would suddenly jerk forward with a loud clang. I got it back the garage, and let it cool.
On restart, moving the lever did nothing - all the way forward and the tractor barely moved at all, and stopped completely when it hit a small crack in the asphalt. I had to push it into the garage.
I figured I would find that the linkage was very sloppy and that my laziness in fixing it led to the drive shaft reaming out the splines on the hydro or yoke.
But ... today I pulled the pan, and put the tractor up on blocks - the rear wheels are sitting on ramps, so they cannot turn. When I turn the drive shaft by hand, the hydro shafts turn - I can see the rear PTO and drive shaft splined spindles turn. Also, the linkage was tight, and no slop to the hydro control arm. I expected to see metal spline shavings all over, but there was no obvious evidence of spline wear (remember the yoke is still in place, so I don't really know the splines are good).
So now I'm thinking the hydro has gone bad on me. I thought I was going to be into sliding the engine forward, pull off yoke and get one of the heavy duty yokes to fix this, but I did not find what I expected. I cannot say for sure if I had control of the deck hydraulics or power steering after the "cool down" event.
Also, I found that a bolt that secures the rear assembly to the frame is missing, and it looks like the frame hole is "wallowed out". There is a pic (5th pic) of this attached. You can move the whole thing back there by hand to get the bolt hole lined up.
The question is ... what are the symptoms of a failed hydro? Does my description indicate the hydro is shot? If so ... that's OK ... I'll either get a used one or take this one to a local shop that I've heard works on them. Since my other one needs work too, I might try both at the same time. It may not be a coincidence that I added oil and all heck broke loose either - there was no leaking oil under the tractor while it was in the garage. Maybe I overfilled?
Thanks for any thoughts on this.


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The two things that will wear out a Sundstrand are high hydro pressures, and dirty fluid that doesn't plug the filter. Both will show as a gradual reduction of performance.

A plugged filter will cause a similar lack of performance to what you report, and it will be accompanied by high fluid temperatures. I don't think that that is you issue, but if the filter has not been changed in the past 200-300 hours, now would be a good time.

The two things to check when one of these hydros suddenly goes south is the drive function (you've done that) and the implement lift/power steering (which you haven't done).

The hydro drive function can fail due to the roll pins holding the swash plate to the swash plate trunnion working their way out of position. This is a take-the-hydro-apart fix, but it isn't expensive (a pair of 1/4"x5/8" spring or roll pins).

The implement lift function can fail if the charge pump drive pin fails. This will also take out the hydro drive function. This is a much easier repair (you only need to remove the charge pump housing), and also an inexpensive repair (one needle bearing 1/8" diameter x about 7/8" long).

The fact that you heard a loud metal bang when things went south indicates to me that something mechanical has failed either in the drive line (your inspection found no faults), or inside the final drive (rear end). If it's inside the final drive, shavings from the damage may plug the filter and cause the symptom noted above.

Note that damage can happen to some final drives that can still allow the tractor to operate normally for several hours before the filter plugs with debris. It's only when the grinding of the case gets loud enough to notice that it is realized that a failure has happened. On my GT, that was after a whole winter's snow removal, about 60-80 hours. Preliminary indications of how bad the failure was, was the shiny silver specs in the fluid as it drained out of the case. In my case, I didn't hear a bang when the bolts holding the differential carrier together broke, but a review of the tasks done over the previous months pinpointed when it occurred. My fault. The Sundstrand hydro is considerably stronger than the final drive and the GT was overloaded with ballast.

Go thru all of the linkages again, both hydro and brakes, and check for wear or damage. On the opposite side of the hydro from the drive control is a stub shaft that is almost flush with the housing. It is the other half of the trunnion shaft holding the swash plate and must move exactly like the control side. No slop allowed. If it moves correctly, the 1/4"x5/8" pins are in place and the problem is elsewhere.

If I recall correctly, there is also a shock absorber involved that can cause problems with the linkage and/or drive function.

The only problem with overfilling the hydro is that the fluid will spill out the vent when it warms up and will need to be cleaned up. If it is low, the drive will be jerky, or non-functional if the tractor is nose high as in climbing a slope. If it too low, none of the hydraulics will work.
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I'm surprised. This is the first 318 tranny issue I have heard of and have never had any issue with any of my 300 series tractors. Good luck. I've seen the complete rear end for a 318 here locally for less than $300.
Minor update. Work has kept me away from the fix.

I jacked it up and ran it, wheels off the ground. The implement lift did not work. The wheels rotate by hand like you'd expect, so at least the differential part works ok ... one rotates forward, the other back, will not move forward together except with a lot of force.
While I had the fuel tank off, I happened to notice that the plastic tube running from sightglass to the top of the pump was broken ... in two places. Well, cracked, but they would leak and could be pulled off by hand.
Pulled filter. It did not look bad .. the oil had no shiny stuff in it, and it was fairly clear.
I dunno. I think I'll try the simple test of new filter, replace plastic tube, fill with oil and see what happens. I give a low probability of success, but heck, a lot of problems get solved because the ON/OFF switch was in the wrong position.
I can get a whole used rear for it for $200 locally ... one more shot with this one.
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Oh, sorry - the important part - the drive shaft rotates the splined shaft/yoke connection properly.
If you find yourself in ohio I have a tranny off of a working 332 id be willing to get rid of for cheap. I hope your other things work though. Its an odd interesting problem ill be following what you do.
Update. I changed oil and filter, and corrected the sightglass tube problems. All oil that came out of the case has been clear.
Tudor directed me to be sure that the shaft on the other side of the case from the linkage arm moves just like the linkage arm side ... it does.
Ran engine with wheel in the air ... the implement lift does not work, and the wheels spin but can be stopped by hand. If I hold both wheels stationary, I can feel the force to rotate them building, but it never overcomes my ability to hold them stopped.
I am now wondering if the pump is somehow being bypassed.
A couple of observations that I never saw before, leads me to wonder if I know how these tractors are supposed to be operated at all. On the top of the pump are two check valves with what appear to be 1/4" shafts that are raised about 1/4" above a hex shaped check valve body. I'm looking at the prints for those valves, but they are blurred and I cannot quite make it out. More important, however, is a wire crank arm with a spring that is attached to the frame, such that the wire can either sit on top of those check valve shafts, and possibly push them down, or just be disengaged from the shafts. On this tractor, that wire crank seems to be out of place (or the hydro is out of place), because the crank arm cannot push down on those check valves - the wire is literally too far backwards to sit on top of the shafts, and no matter what position the arm is in, it does ... nothing. The spring on it lets you pull the lever out from the side, and possibly locks it into a position, but again, I do not know what it is supposed to be doing. On my other tractor, this arm sits directly on top of the shafts of the checks, and it looks like it is holding those check valve shafts down, but its hard to tell.
Is this crank arm intended to be pushed on, or released, to operate the checks, so that you can tow the tractor and the oil is bypassed around the pump? The lever arm for the crank is on the right side of the tractor, right at the frame ... I never noticed it before as I think it would be covered up by the seat pan.
i tried to push on these shafts but they did not seem to move.
Until one of you comes up and says, "Hey, dummy, everyone knows that this lever is the Release to Tow lever, and OF COURSE it engages the checks ... that's how it bypasses, you idiot!", I'm going to do a better comparison of the two tractors I have in this area, and also keep looking for the owners manual in pdf - my hardcopy got wasted in a fire recently. I'm hoping the manual tells me what this lever does, and what position it is supposed to be in for operation. My current working theory is that the hydro shifted forward somehow (look at the missing bolt photo in my original post), which rendered this mysterious lever non functional, and what I need to do is fix that. Somehow.
Wife pushing me to buy a "better tractor" and give up.
She does not get it.
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The "wire lever" I'm talking about is in the third photo in my original post where you are looking down at the top of the hydro pump ... it is bent like a shallow square corner U, with pivot supports on the frame. You can see where the bottom of the U contacts nothing, but if repositioned, would contact the check valve tops.
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TUDOR;12320411 The implement lift function can fail if the charge pump drive pin fails. This will also take out the hydro drive function. This is a much easier repair (you only need to remove the charge pump housing) said:
The charge pump pin would be my guess if you have no implement or power steering function.

The two "buttons" on top of the check release valves are supposed to be up for driving and down for pushing, so as long as they are up, the mechanism to push them down is not the present problem.
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WELL! If anyone is still following this thread, have I got treats for you! In this installment of "318 Tractor Vandalism", we will get all the way to pulling the rear, charge pump and transmission ... but no spoilers for what happens in the end!
After a LOT of whining and hoping, I committed to the repair. A buddy of mine put me onto the manual, which helped a little, but frankly, all it did was confirm what I thought I should do.
First i did a much better job of draining the oil and found essentially a paste on top of the drain plug. It was almost like moly grease. There was very fine metal particles in the oil that came out with the plug - a lot of it.
Disassembled the brake drive rods, pulled the hoses (which was NOT the big deal I thought it would be), and now, the main event. Take out the four bolts holding the rear to the frame. Now there is supposed to be a fifth bolt into a lateral strut frame member, but mine was gone (ominous music here).
I had to use a tire iron X to break those bolts free, and what I found was ... unexpected. On both sides, the frame was completely cracked away where the bolts go through. I do not know what was keeping it all together. The attached photos tell the tale.
Problem #1 Frame needs structural repair. Problem #2. Hydro does not work, and you have to wonder, with all the metal in the oil, is it worth it?

I'll tackle the frame later. I rolled the rear assembly away from the tractor, saturating every square inch of driveway in oil, and started in with a toothbrush and simple green. Degreased the whole thing, photo. Now ... here we go. Pull the charge pump. The consensus, without the metal in the oil info, is that I will find the charge pump pin sheared. Photo shows the perfect pin in place. Reassembled pump.
At this point I am CERTAIN that I will pull the transmission and find that the differential drive bevel gear is completely wasted. I do not know how that would stop the implement function from working, but that is what I thinking at the time with wrench in hand. Doesn't matter, the transmission has to come off.
Another four bolts which were darn stiff to get off and pull the pump/transmission assembly.
This revealed a gleaming bevel gear and a beautiful set of differential gears inside. Photos attached.

And now its going to rain. Rolled the differential rear into the garage, plugged up the hole, and put the transmission on plastic ready for disassembly. I've got some garage cleaning to do before I can tackle that task on a clean bench. Obviously, the transmission is hosed. Considering how much metal I found ... it might be a nice dog run anchor.

Regarding the frame fix, I'm thinking about grinding away the entire tab that bends out on both sides and replacing with some thicker angle iron, bolted and possibly welded to the frame. That'll be fun. It'll be another few days before I have anything useful to update.
Thanks for any ideas or thoughts in advance.


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Tractor is back up and running. Ultimately, I ground off the old frame brackets that were cracked, bolted some 3/16" thick angle iron to the frame to make new brackets. Used many new screws to assemble all of it. Painted, etc. Got a new pump/motor, O rings, assembled. Slipped the rear back on the frame, a billion bolts and brackets, etc. Put in a new shock absorber in the linkage. Put rear up on jacks, ran engine, adjusted hydro linkage - very sensitive linkage. New battery.

Runs much better than it ever has now ... now I know how the hydro was supposed to work!
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So there wasnt anything broken in the trans?

Great job fixing it up.
Well I would say that someone up above maybe had the pump stop working so you'd have to take that apart and find the major issue that was getting ready to cause you some real grief! Put an extra $5.00 in the collection plate this weekend! Glad you found and fixed your issue and got that frame taken care of too!
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I had to use a tire iron X to break those bolts free, and what I found was ... unexpected. On both sides, the frame was completely cracked away where the bolts go through. I do not know what was keeping it all together. The attached photos tell the tale.
Now you have an idea of just how much torque a Sundstrand can deliver. Someone was either pushing dirt around with a front blade, or had a FEL on that tractor at some point that didn't have the subframe correctly mounted.

That doesn't explain why the hydro failed. The charge pump appears to be pristine and it is where the fluid enters the hydro. If it is getting fluid at all, the implement lifts should work. If it isn't getting fluid, nothing will work. Your initial problem was either with the filter or the supply tube from the final drive. Since a fluid and filter change did not correct the initial problem, I suspect the supply tube was the fault, either cracked (sucking air), or plugged.
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