How Massey Ferguson GC 1723 & 1725 hydraulics are plumbed

   / How Massey Ferguson GC 1723 & 1725 hydraulics are plumbed #1  

dicktill

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Allegany NY
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Massey Ferguson GC 1723EB
How Massey Ferguson GC 1723 & 1725 hydraulics are plumbed - part 1

A lot of this should be applicable to other GC model tractors. Also, as I describe, I am new to all this so please point out any errors. Sorry, very long post. : (

1 I just bought my first tractor, a 2023 Massey Ferguson GC 1723EB (TLB model with backhoe) last year; she is named "Fergie". Being what I am, a retired mechanical engineer, I wanted to modify the hydraulic circuit (top & tilt, third function, hydraulic backhoe thumb, etc.), but also wanted to know what made it tick. Although I have worked on many different types of machinery, this was my first experience with hydraulics except for floor jacks and such. I read up about hydraulics on TBN, YouTube, and supplier websites, so I sort of understood “power beyond”, valves, etc. Yeah, about as good as I understood women.

2 Nomenclature:
- TBL = tractor-loader-backhoe
- ROPS = roll over protection system
- FEL = front end loader
- FEL valve = front end loader valve, aka joystick
- left and right refer to aft-looking-forward, i.e., as seated
- T marking = return to tank
- P marking = pressure inlet
- PB marking = pressure beyond outlet; note that just as “one man’s floor is another man’s ceiling,” the “pressure beyond” from one device becomes the “pressure inlet” into the next

3 Tracing lines on the tractor and studying the 388-page service manual had me scratching my head – a lot. Some of the schematics seemed to be incomplete and/or disagreed with others, and actually hydraulic schematics remind me of petroglyphs. The photos in the manual are fairly good, but the lines aren’t annotated on them. Also confusing is that this manual doesn’t cover the backhoe.

4 I had a bit of downtime while I was waiting for a new front tire, so I pulled the seat, ROPS, fenders, and ROPS support off. I pumped most of the fuel out of the tank but didn’t want to drain the remainder all over the machine, so I didn’t disconnect the fuel feed from the tank and hence could only pull the tank back a few inches. I was somewhat able to better trace the lines, but having the tank out of the way would have been better.

5 I was finally able to find the hydraulic oil pump which is external to the transmission and on the left front. Hmm, how does the oil get from that to the filter on the lower right? Ah, I’m used to car engines where it goes sump > strainer > pump > filter > bearings & such. Duh, it would be kind of rough on a cartridge filter to put 3000 psi in it, so that happens later on in the system, sort of on the return system; more on that in paragraph 11.

6 On top of the pump and bolted to it is a unit they call the “control valve.” Finally figured out that this was the 3-point hitch control valve (more on that in the next paragraph) even though the lever for that was on the right side of the machine. Sandwiched between the pump and the control valve is a “line filter” #3757286M1; this appears to be another strainer and I assume that this also functions as a seal between the two components as no separate O-ring is shown. On the 1723/1725, the front loader joystick (aka, FEL valve) is also on the right-side fender (earlier GC models had it up “on the dash”). There are three hard lines shown in the manual that come from the FEL valve (actually from some sort of adapter plate attached to it). The bottom two both go to different ends of a funny block/fitting on top of the control valve (officially called “flange cover” #6259421M1), and the third (top) line goes aft to somewhere on the transmission. I disconnected this line, started the machine, and nothing came out unless I wiggled the joystick around. So, this must be the return line to the tank. Because I have the backhoe model, the rearmost of the other two hard lines has been replaced by hoses that go to the backhoe. The hose from the FEL valve goes to the yellow coupler that then goes to the backhoe valve pressure port; this is “pressure beyond” from the FEL valve. After the hydraulic oil has passed through the backhoe valve, there is a pressure beyond port that is connected to the blue coupler, and then on to “flange cover” on top of the control valve. What has been done here is the same as if the original hardline was still there from the lower rear port of the FEL valve to the “flange cover.” Also, if the backhoe is removed and the yellow and blue couplers on the tractor are connected together, the circuit is the same. The third coupler for the backhoe is red and is the return to tank. The third hard line from the FEL valve, the lower front one, goes up to this same “flange cover” on top of the control valve. What the …, does the flow go in on one end and back out on the other?

7 After much more poring into the manual and the parts books, I discovered two things. First, this “flange cover” is bolted to the control valve and there are two O-rings in between, meaning the two circuits are independent (i.e., there is a bulkhead in the block). Second, the so-called control valve isn’t just the 3-point hitch valve as I insinuated in the previous paragraph, but also contains the main pressure relief valve and a flow divider, BUT these are isolated from the 3-point hitch valve, except perhaps a return to tank line. So this entire “control valve” contains various different components.

8 Here's how I think it all works. The pump gets its oil through a strainer at the left rear of the transmission. It pumps this up into the left side of the control valve where the main pressure relief valve can open and send it back to the tank. It also is plumbed to a dividing valve which sends some of the flow out of a fitting on the left side of the control valve and off to the steering wheel control valve; the rest of the flow goes up to the “flange cover” and on to the FEL valve; both of these are essentially “power beyond” ports to the steering valve and the FEL valve.

9 In summary, the three lines on the FEL valve are:
top – return to tank – T or R
lower front – pressure in - P
lower rear – power beyond to the backhoe if applicable and then to the 3-point valve, otherwise directly to the 3-point valve - PB

10 The power beyond line (from the FEL valve or the backhoe) to the control valve goes through the “flange cover” and into the right half of the control valve which contains the 3-point hitch valve. There are two fittings on the right side of the control valve. The forward one goes to the “slow return” valve for the 3-point hitch, and then to the 3-point lift cylinder (which is single acting). Fluid going from the 3-point valve to the cylinder meets no resistance, but the flow coming back can be throttled down to slow the descent of the 3-point hitch. The rear of the two fittings is plumbed back to the tank. The “slow return” valve is not shown in some of the diagrams.

11 In paragraph 8 I discussed the dividing valve within the control valve, and the power beyond line to the steering valve. I won’t delve into this anymore at this time as it is fairly well covered in the service manual, except that the “tank return” from the steering valve really doesn’t go to the tank. It actually is tee’d to go two places. One is the PTO (power takeoff clutch, which I won’t go into as I haven’t used and studied that), and the other is (finally!), the filter. From the filter, the fluid runs to the hydrostatic transmission. So, the transmission is the only component that is working with freshly filtered oil, and the only component that returns relatively clean oil to the tank! As far as I can tell, it is only the flow through the transmission that gets really filtered. Everyone else is taking what feeds back to the tank through various components (and isn’t filtered either before or after use) and is then only strained on its way to and from the pump.

12 The service manual diagram for the complete system is vague, confusing, and … wrong! I scratched my head on that a lot, finally figuring out that they had gotten the rectangular outline of the FEL valve mixed up with the hydraulic lines and that they had also had not clearly defined who was tee’d to who and who was not. A week after this, I searched the web for “Massey Ferguson GC hydraulic diagram,” in the hope that they had printed something better. I found a TBN thread: “Help with MF GC 1705 to 1720 series Power Beyond...“ by @WranglerX in 2019 in the “hydraulics forum”, and in it, he had found the same error, and offered the same solution. Wish I had found that thread earlier as it would have saved me a bunch of time and head-scratching! A couple of years later, he also documented/pointed to another thread: “GC1705 Project-additional hydraulics” by @ 07keo02, located in the “Massey Ferguson owning/operating” forum; there’s good information in that one too. Here’s @WrangerX’s corrected diagram:

gc1715.jpg
 
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   / How Massey Ferguson GC 1723 & 1725 hydraulics are plumbed
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#2  
How Massey Ferguson GC 1723 & 1725 hydraulics are plumbed - part 2

A lot of this should be applicable to other GC model tractors. Also, as I described in the first post, I am new to all this so please point out any errors.

Belated answer to the question @WranglerX asks in the hydraulic schematic posted above: Yes, without a backhoe, the FEL BP port connects directly to the control block for 3PH. The phantom box on the lower left is the entire so-called “control valve.” Within it is the 3-point hitch control valve (upper right). The dividing valve is shown (center left) as well as the main relief valve (lower middle). The smaller attached rectangular box on the right just above the “9” is the funny fitting/block. The line going off to the left, between the “12” and the “13” is the power beyond to the steering valve.

13 I still wonder about why they put that “flange cover” (see paragraph 6) on top of the control valve if it is just a block with two separate openings in the bottom (that are sealed to two different passages in the control valve), and fittings at opposite ends. Why didn’t they just drill and tap the top of the control valve directly for the fittings? Perhaps if the control valve is used on a model without the joystick/FEL valve, then there is a substitute block that just bolts on top of the control valve and connects the two ports together. Perhaps that’s what they are showing here (note the “slow return” valve is missing):
control valve hydraulic circuit.jpg

14 Another summary explaining the flow paths; the many tank returns are omitted, as are additional relief valves:

tank > strainer > pump > strainer > main relief valve > flow divider >
----- > steering valve > steering cylinder > tee >
----------- > oil filter > hydrostatic drive
----------- > power takeoff valve > power takeoff clutch
----- > front end loader valve >
----------- > lift & curl cylinders > backhoe valve (if equipped) >
---------------- > backhoe cylinders (if equipped)
---------------- > 3-point valve > slow return valve > 3-point cylinder
 
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