Sundstrand 15 U type tranny leak...

1907 Views 41 Replies 6 Participants Last post by MrBorland, 2 mo ago

MrBorland

Discussion Starter · 3 mo ago

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...

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MrBorland

Discussion Starter · #3 · 3 mo ago

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

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MrBorland

Discussion Starter · #4 · 3 mo ago

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?

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MrBorland

Discussion Starter · #6 · 3 mo ago (Edited)

TUDOR said:
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?

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MrBorland

Discussion Starter · #8 · 3 mo ago

TUDOR said:
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...

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MrBorland

Discussion Starter · #11 · 3 mo ago

TUDOR said:
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

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MrBorland

Discussion Starter · #13 · 3 mo ago

GreenGabby said:
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...

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MrBorland

Discussion Starter · #15 · 3 mo ago

GreenGabby said:
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.

GreenGabby said:
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.

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MrBorland

Discussion Starter · #19 · 3 mo ago

GreenGabby said:
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.

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MrBorland

Discussion Starter · #21 · 3 mo ago

GreenGabby said:
I am going to assume this was a mod during earlier service

I never thought of that, but makes sense, since I've not yet seen any schematic showing set screws. Custom mod or not, I'll need to find that pin - the yolk was drilled for those set screws, and the hole is bigger than the diameter of the pin (see photo, post 11), so methinks I'd be asking for trouble installing a standard pin. I'll have to replace the yoke if I can't find that pin.

Thanks again

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MrBorland

Discussion Starter · #23 · 3 mo ago

GreenGabby said:
I don't understand how the set screws solve anything...The pin isn't doing anything but filling a hole drilled in the input shaft.

I haven't measured anything yet, but off the top of my head, I sketched out how I think looks. The modified pin is a bit longer than the input shaft, and the cone-shaped set screws screw into the ends of the pin. But yeah, not sure why the set screws were needed.

GreenGabby said:
If the pin does protrude into the yoke and the hole diameter in the yoke is larger than the hole in the input shaft the rocking action between the yoke and shaft is only going to shear the pin again

Correct; which is why I was thinking putting a standard pin in the existing yoke is asking for trouble.

GreenGabby said:
Personally I feel you may need to replace the yoke to get the correct one on the tractor.

I'll take another stab at finding that custom pin - otherwise, I'll have to buy a yoke & pin.

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MrBorland

Discussion Starter · #24 · 3 mo ago

TUDOR said:
Drop the driveshaft for a look see.

Just got in for a look-see. Drive pin looks fine to me. I suppose the next step is to button it back up and check pressures?

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MrBorland

Discussion Starter · #26 · 3 mo ago

TUDOR said:
Have you corrected the leak mentioned at the start of the thread? Does the transmission work?

Thanks for checking in. I freed up the check valve plungers, and that stopped the leak, but the tractor still wouldn't move nor the hydraulics work (see post #4). It was at that point, the charge pump drive pin became suspect, which turned out to be ok.

I'm at a crossroads, now - do I re-install the driveshaft and do some pressure testing, or are there things to look at before I re-install the driveshaft? For example, when removing the charge pump, the outgoing implement line was just a smidge in the way, so I disconnected it - I was expecting fluid (or some evidence of it), but looking back, it seemed dry. Is that a clue? The implement check valve didn't seem dry and the pin seemed to be able to move freely. The charge check valve seemed ok as well. I suppose the filter could be clogged, but it's a brand new Wix hydraulic filter. Worst case, I suppose, is that the pump itself is toast.

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MrBorland

Discussion Starter · #28 · 3 mo ago

GreenGabby said:
The input shaft to the charge pump is direct drive to the pto output shaft on the top rear of the transmission. If you start the tractor the input and output shaft should both be turning with no activation of the hydrostatic/hydraulic functions. Engage the hydrostats or a hydraulic function. Do both input and out continue to turn? If not you still could have a problem in the input shaft pin.

Good tip

GreenGabby said:
A member informed me I installed the pump cover ... upside down. I didn't believe it was possible but after I rotated the cover 180° everything worked fine. Try it

Yup - the charge pump is a bit off center between the bolt holes, so everything needs to go back on as it came off. That said, since the yoke was futzed with, I should double-check that the charge pump also wasn't futzed with and put on backwards, in which case, I might've managed to re-install it backwards as well

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MrBorland

Discussion Starter · #30 · 3 mo ago

TUDOR said:
Check the shaft on the side of the transmission that controls direction and speed. There is a similar shaft on the other side that must move in harmony. It may only appear as a stub shaft that is flush with the housing, but nevertheless, it should still turn.

I checked it by moving the shift lever to & fro, and the shift & stub sides move together.

TUDOR said:
Back to the charge pump. The guts of the charge pump cannot be installed wrong. However, if the charge pump cover is installed wrong, the pump parts will conform to the cover and neither the implement lift nor the hydro will function

According to the manual, the flat side of the casing should be on the relief valve side, which makes it easy to check. I double-checked this morning, and it looks correct.

I need to order to order another yoke/pin, at which point, I'm leaning towards re-installing the driveshaft to take some pressure readings. My gut is increasingly telling me, though, that it's likely the tranny needs to be dropped and the pump rebuilt. On one hand, an unexpected issue, but on another, exactly why I bought this tractor - to learn as much as I can. Getting into a hydro pump is definitely new and something useful to learn.

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MrBorland

Discussion Starter · #32 · 3 mo ago

TUDOR said:
Pressures should be zero in the hydro until such time as the charge pump and implement lift system is working. The charge pump ensures that the hydro has fluid to work with.

Right, but do we know for sure the issue is the charge pump? A pressure reading would be diagnostic, no? What if there turns out to be pressure in the charge circuit? - wouldn’t that suggest the hydro pump itself is the issue?

And speaking of weirdness, what are the chances there’s a blockage TO the charge pump? Filter, suction tube, etc. Easy enough to check, I suppose.

Thanks for your & Gabby’s continued help & patience - I really appreciate it 👍

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MrBorland

Discussion Starter · #35 · 3 mo ago (Edited)

GreenGabby said:
.does your oil level indicator hose have the breather installed above where you checkt oil level? Breather is between where you check oil level and an adapter back into the transaxle. Without this breather you will not get an accurate oil level in the tube

TUDOR said:
Charge pump is first on the diagnostic list for a reason. Follow the path of the fluid, reservoir, filter, charge pump charge relief valves, hydro charge relief valves, and last is hydro

Thanks. With the driveshaft disconnected, I've visually inspected the charge pump, relief and check valves and all seem ok. At the back end, the tubing is new, and I had already installed a new breather, but I can check to make sure it's actually doing its job.

When we suspected the charge pump drive pin was sheared, I found it was easiest (and most cost-efficient) to order a replacement charge pump (which came with a pin). As mentioned, the charge pump seems ok, but I swapped it out for the replacement anyway.

Beyond this, unless there's something else to look at, I'm thinking it's time (once I get the replacement yoke & pin) to re-connect the driveshaft to see if the charge pump swap made any difference.

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MrBorland

Discussion Starter · #36 · 2 mo ago

An update:

I received the new yoke, and to my surprise, it's exactly the same design as the old one, so apparently, the set-screw design wasn't a modification.

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Also, the instructions indicate there's no pin in there at all, so I'm not sure what I drove out with a punch - maybe just some Loctite goo? It would explain why I was never able to find the pin.

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Anyhow, after installing the replacement charge pump, and re-installing the yoke and driveshaft, I started it up, and...no improvement

. I opened the air bleed line in the back and manipulated the drive control to see if it would help bleeding the air. No improvement.

After running for a few, minutes, however, the engine really started to struggle - not sputtering like it was running out of gas, but bogging down like it was getting ready to seize. I quickly shut it down and went inside for a cold adult beverage so I could think about this a bit more.

So, putting some pieces together...here's what I'm now thinking...the engine oil level is fine and the oil is still very clean. Recall the original charge pump visually looked ok and a replacement didn't fix the problem, so I'm thinking the issue isn't with the charge pump itself. After I shut it down, I opened the small access charge pressure testing port on the top of the pump - I expected to see fluid in there but didn't. And I recalled no fluid came out when I swapped charge pumps. So...I'm thinking it's the hydro pump that's bogging the engine, and that it's bogging the engine because it's oil-starved, and that it's oil-starved because of a blockage between the reservoir and the charge pump. Makes sense? Thoughts? Alternatives?

If my hypothesis is correct, I hope the hydro pump isn't irreparably damaged. Seems to me the easiest thing to do at this point is to drop the filter to at least see if there's fluid in there. A lack of fluid suggests a blockage somewhere between the filter and the reservoir. If there is fluid in there, the blockage (assuming there is one) would have to be between the filter and the charge pump. Maybe the filter itself is bad? Off the top of my head it's a WIX 51410, which, according to the interweb, ought to be the correct filter. Thinking back, I didn't pre-fill the filter, and maybe that was an important step to "prime" the circuit?

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MrBorland

Discussion Starter · #39 · 2 mo ago

TUDOR said:
Any hydraulic pump that is starved for fluid will freely spin. It will not cause the engine to bog.

I was guessing the fluid also provides needed lubrication for the spinning stuff connected to the input shaft (pump/pistons, charge pump). Not so?

GreenGabby said:
It sounds more like electric pto out of adjustment. Nothing to do with hydraulics. Have you done anything with the pto?

Rear PTO? The tractor isn't equipped with a rear PTO. I had the front PTO off when I rebuilt the engine. It's back on and adjusted according to the service manual, but I didn't hook the wire up yet - I figured since I'm not going to use the deck, I'd just leave it unhooked until I dial everything else in.

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MrBorland

Discussion Starter · #42 · 2 mo ago

old geezer said:
If oil is leaking out of suction tube it will be sucking air instead of oil. The fitting is 37degree JIC. The o ring is between fitting and housing. Line is metal to metal. Line is either loose or cracked. New pump without oil will seize and cause engine loading. Fix the leak ,then remove pump to inspect. Polish parts or install old pump and lubricate before startup. Remove filter and fill with oil to reduce dry run time.

Thanks.

I suspected I should've pre-filled the filter and that that's maybe why fluid wasn't circulating and that something in the dry hydro was dragging the engine. I removed the filter and confirmed it was still empty. When reading the service manual, I was "in the weeds", reading the section about the inner workings of the tranny, and it didn't say anything special about the filter installation. I see now, in the "regular maintenance" section, it indicates the filter should be pre-filled. Dumb mistake.

I'll check out the charge pump and pre-fill the filter. I'll inspect the suction tube for cracks as well. While I've got the driveshaft disconnected again, I'll run the engine to be sure the bogging isn't primarily an engine issue.

I'll keep you posted.

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