[MrBorland]

I bought a non-running John Deere 300 sometime ago and just finished rebuilding the engine. The engine runs fine now, so I hooked up the driveshaft, started it up, and immediately saw tranny fluid is leaking pretty heavily out of the the upper fitting of the suction tube (next to the filter), and I'm looking into why it could be leaking so bad. If anyone's got a guess, please pass it on. FWIW, the check valve adjuster is backed all the way out, but the tractor doesn't move when the lever is moved forward or reverse.

The manual indicates this is a 7/8-14 "O-ring" type of fitting - does this indicate there should be a separate O-ring on the fitting? The fitting's plenty tight, but a missing O-ring could certainly cause a leak.

If I'm reading the circuit diagram right, should be part of the suction flow to the charge pump. If the tractor doesn't move when the shifter is moved, and the suction tube leaks, could the charge pump be creating back pressure?

I haven't yet removed the fender deck to look at the check valves. They were rebuilt, but I suppose the plungers could be stuck in the down position, which would explain why the tractor doesn't move. Would this also explain the leak? Does running the engine/tranny with the check valve plungers depressed create an over-pressure situation which would cause a leak?

If any of you Sundstand experts have any ideas about where to start looking, let me know...

 

[PA318Guy]

Did you check the level of the trans fluid? The only time I've had that happen was when I overfilled one.

 

[MrBorland]

Actually, it was a bit low.

I'm reading the threads need sealant. Hmmm. When I got the tractor, I dropped the suction tube and changed the fluid with new HyGard, but didn't know about the need for thread sealant. I can drop the suction tube again (and try to collect the new Hy-Gard that'll drain), clean the oil from the threads and reseal if that's the likely issue. I might even read the service manual this time

 

[MrBorland]

An update:

Even though I backed out the check valve adjuster, I was suspicious that the check valve plungers remained depressed, so I removed the fender deck and took a peak. Sure enough, the plate that the adjuster pushes down on to depress the check valve plungers apparently lost its spring, and was keeping the plungers depressed. Once I removed that plate, the plungers came right back up. I topped off the tranny fluid, started the tractor, and no leak. Terrific.

Unfortunately, the tractor still wouldn't move, and the hydraulics don't seem to move the rocker shaft under the tractor. I don't yet have a pressure gauge, but I inspected the control valves on the top & side of the pump, and they're clean, the springs are fine, and the plunger moves freely. I suppose the charge pump could be toast, but the earlier leak seems to be from pressure buildup, suggesting the charge pump is fine & building pressure.

I haven't seen it yet in the manual, but does the system need the air bled after a fluid change? Do the hydraulic levers need to be worked back and forth to get fluid where it needs to be? I worked those levers, but I'm wondering if they just need to keep working until the hydraulics start working. Thoughts?

 

[TUDOR]

Quick and dirty diagnosis for charge pump issues of a Sundstrand series 15 hydro. If the hydraulic implement lifts do not work, the charge pump drive pin is broken, Replace the drive pin.

With the pin broken, the charge pump cannot pump fluid. Fluid can only move to the outside if driven by pressure. The supply side components (tube from the reservoir to the transmission and the filter0 are under negative pressure (vacuum) and unlikely to result in a fluid leak unless an O-ring is missing or a fitting is cracked. An air leak to the interior is much more likely.

 

[MrBorland]

Quick and dirty diagnosis for charge pump issues of a Sundstrand series 15 hydro. If the hydraulic implement lifts do not work, the charge pump drive pin is broken, Replace the drive pin.

With the pin broken, the charge pump cannot pump fluid. Fluid can only move to the outside if driven by pressure.

Thanks. Very helpful. The video below was also helpful to visualize and understand the role of the charge pump. The charge pump replenishes the drive circuit with leaked fluid, so if it isn't working, the drive circuit doesn't work because it runs out of fluid ("cavitates"). It seems easy enough to pressure-test the charge and implement circuits, so I'd like to do that before dropping the driveshaft to get to the charge pump.

From the animation, it also appears that if the check valve plungers are depressed while the engine is running, the pressure in the circuit forces fluid backwards into and past the charge pump, and into the normally-low suction line, explaining the leak, and why it was "fixed" by letting the check valve plungers return to normal. In fact, if the drive pin is sheared, maybe this is why it got sheared - forward flow of the charge pump battling back pressure from the open check valves?

 

[TUDOR]

Another name for the check valves is cross-port relief valves. When one is closed, the other is open to the low pressure side of the hydro. The above diagram shows both as being open in an active system, which isn't going to normally happen.

Pumps are designed to flow fluid against pressure. To get fluid flow backwards through through the pump means that the pump is broken and there is a secondary method of moving fluid. Possible, but not likely.

 

[MrBorland]

The above diagram shows both as being open in an active system, which isn't going to normally happen.

Right. But I'm curious what happens when they are both open in an active system - i.e., plungers depressed to push the non-running tractor, then remain depressed when the tractor is started? I don't recall this being discussed in the service manual. Seems like it'd be easy to do, but bad for the tractor.

I bought this tractor in non-running condition. After I rebuilt the engine, I also changed the tranny fluid, so what's the likelihood the charge pump simply needs to prime after the fluid change? OTOH, if the charge pump drive pin is sheared, would running the engine/tranny damage the pump? Would running the pump to run it long enough to take a pressure reading damage the pump, or do you recommend just dropping the driveshaft and opening the charge pump to take a look-see?

Thanks for all your great help...

 

[TUDOR]

When both check valves are depressed, the fluid follows then path of least resistance back to the reservoir. There is always internal leakage and there is only 0.913 cu-in of fluid in the motor.

Drop the driveshaft for a look see.

 

[GreenGabby]

MrBorland, sending you a private message ... Gabby

 

[MrBorland]

Drop the driveshaft for a look see.

A replacement pin is surprisingly difficult to find, and shipping is twice the cost of the pin. I ended up ordering a charge pump (which includes the pin & o-ring) for not much more, in the event the charge pump is damaged in any way.

I managed to get home early today, so I dropped the driveshaft. Unfortunately, the rear hub wouldn't come off the input shaft (just in front of the charge pump), even after the set screws were removed. After reading the manual, I suspect there's a pin inside there that needs to come out. Unfortunately, according the the manual, it might involve removing the tranny & using a press to get that pin out. If I've got this wrong, or has any alternative ideas, let me know

 

[GreenGabby]

Key # 13 is a roll pin that needs to be driven out to remove the driveshaft.

https://partscatalog.deere.com/jdrc/sidebyside/equipment/66822/referrer/navigation/pgId/181400

 

[MrBorland]

Key # 13 is a roll pin that needs to be driven out to remove the driveshaft.

Yup - I just confirmed that too. Unfortunately, according to the manual, the entire tranny needs to come out, the pump removed and taken to someone who can press the pin out. I was hoping for an easy fix, but Murphy's biting me on this one. What a crazy design...

 

[GreenGabby]

I do not know what manual you are reading but my comment is bull. I have remove quite a few driveshafts. The worst I found was on a 314 were that roll pin had sheared but the pieces bound and driveshaft continued to function for quite a while. Broken pin wallowed the bore in the transmission input shaft to the extent I needed to replace the charge pump.

 

[MrBorland]

Key # 13 is a roll pin that needs to be driven out to remove the driveshaft.

I already dropped the driveshaft. The next thing that needs to come off to open the charge pump is the hub, which is between the driveshaft and the charge pump (part #15 in your schematic), and it looks like pin #13 needs to come out to remove the hub. The manual indicates it needs to get pressed out.

I do not know what manual you are reading but my comment is bull. I have remove quite a few driveshafts. The worst I found was on a 314 were that roll pin had sheared but the pieces bound and driveshaft continued to function for quite a while. Broken pin wallowed the bore in the transmission input shaft to the extent I needed to replace the charge pump.

Can that pin be driven out with a punch and the tranny in place? I'm soaking it in penetrating oil and can support the input shaft, and at least give it a try.

 

[GreenGabby]

Yes, it can be driven out with the correct size pin punch and a ball peen hammer. I have never needed to soak the roll pin. I am just wondering however if the same thing has happened to you. Pin may have sheared and turned binding the ends of the pin in the ID of of the driveshaft yoke. You may need to slip a pipe or crowbar thru one of the yokes to lock the driveshaft from turning then rock the tractor back and forth to see if the transmission input shaft turns in the yoke.

My 314 gradually lost ground speed was first indication something was wrong. I also have 3ph on the tractor and was losing hydraulic power. Suddenly I lost all ground speed and hydraulic power. The yoke and input shaft were no longer bound but as mentioned serious damage had already occurred. Hopefully you can get the bore in the shaft aligned with the bore in the yoke to drive the pin out.

 

[Nouveau Redneck]

Another method is to drill it out with a bit that is just slightly smaller than the hole.

 

[GreenGabby]

But before drilling you need to make sure the holes are aligned so you do not damage the input shaft.

There should be a post over on WFM I wrote covering this repair. I thought I might have some photos of this repair but could not find them.

 

[MrBorland]

Yes, it can be driven out with the correct size pin punch and a ball peen hammer. I have never needed to soak the roll pin.

I went out before work this morning, and to my delight, the pin easily tapped right out with a 1/4" punch. I managed to get the hub off as well. Unfortunately, the pin fell somewhere into the gravel, so I'll have to root around with a magnet to find it.

Interestingly, the hub in your schematic (and my parts manual) shows just a 1-1/2" pin, but mine also uses a pair of set screws to secure the pin. I have to find the pin, of course, but looking at the shaft, the hub, and the set screws, I'm guessing the pin is shorter than 1-1/2".

The charge pump drive pin should be coming in the next few days, so I'll post an update then. 🤞

Thanks for your help.

 

[GreenGabby]

I am familiar with the pin being longer than the OD of the yoke. Drive in the new pin then push wire thru the pin and wrap the ends with a pair of pliers. Wire is installed to keep the pin from walking out. Set screws would do the same thing but I have never seen this being used. I am going to assume this was a mod during earlier service. Glad to hear you are getting task completed ... Gabby