Case DH4B Trencher/Backhoe Won't Spin Trenching Chain

[r8f1k]

I just acquired an older DH4B, Mitsubishi diesel, runs fantastic, backhoe works, but the trenching chain does not. If I pull the lever to move the chain forward or backwards, it will move JUST SLIGHTLY. Maybe one tooth, then stop. You can hear the hydraulic pump working, but nothing is happening. The linkage on the pump is free and you can see it move no problem. On top and on bottom of the pump looks to be two compression style clamps that turn a rod that passes all the way through the pump. They look like they can be adjusted, but I am afraid there is something more going on here. I have plenty of hydraulic fluid and the engine revs up just fine when more RPMs are needed. I should also note that the push blade in the front does not move at all. It is almost like there is no hydraulic pressure going to the valve body. I am wondering if I am missing a hydraulic line altogether. Any ideas would be great.

*Update, I disconnected the hydraulic pressure line to the trencher hydraulic drive motor, when I did that I can turn the digging chain around a whole lot more. When I pulled the hose, water came out of the hydraulic motor, it is January up here in the north and I was wondering if the motor was full of ice. Gonna let it thaw out in the shop.
The thing that I am wondering, is that I am seeing on the parts diagrams a 'selector valve' for the hydraulics. With the trencher not working AND the back fill blade not working, could there be a selector valve that I am missing? Is the hydraulic system split 50/50?*

 

[r8f1k]

Checking the internet, I found my model and I see in this photo another hydraulic lever that I don't have. Is that the SELECTOR? My machine has been painted a second time and all the labels are gone.

 

[oldnslo]

Can you follow the hoses from to the pump to see what they connect to? This should provide a starting point on what valve or valves are in that circuit. From your initial description of the pump control I am wondering if that is a hydrostatic drive with no directional valves in the trencher circuit.

 

[r8f1k]

I can try, it is a NEST of hoses. There are two pumps on the back of the engine, I can hear the one on the right start to click when I engage the lever. I hope it isn't bad.......The machine is a hydrostatic drive for propulsion, not sure if it is for the trencher.

 

[oldnslo]

Can you tell What the lever that operates the trencher connects to? A directional valve or pump control linkage?

 

[r8f1k]

The trencher control is a cable driven lever, forward, neutral and reverse. The cable pulls on a shaft that runs up and down in the center of the right side hydraulic pump behind the engine. I assume it is simply changing the direction of flow to the hydraulic motor under the seat. I wonder if I disconnect or make the fitting loose at the motor and see if I have pressure, that will determine if the problem is the motor or the pump?

 

[oldnslo]

If directly controlling pump sounds like hydrostatic drive. This requires a closed loop to prevent damage to the pump. Disconnecting one hose to the motor will allow to escape this loop and if enough oil escapes will damage the pump. The fact that engine grunts and chain moves a little points towards pump trying to work.

Do you have the capability of installing pressure gauge in the lines at the motor? This will tell you if you getting pressure to the motor.

 

[r8f1k]

I can buy a gauge and work from there.

 

[5030]

Just curious, ever bother to check the fluid level?

 

[r8f1k]

Fluid level is just above the FULL line. I drained all the old fluid out before trying to start the unit up, I wanted to make sure any trash, water or sludge that was in the system was removed prior to circulating it through the system. Took about 13 gallons to fill it up, not including what was still in the hoses.

 

[oldnslo]

I can buy a gauge and work from there.

R8
If you install a gauge and this is a hydrostatic drive you should see charge pressure anytime the engine is running. Charge pressure typically is between 150 & 350 PSI. When you try to operate the trencher pressure should rise to relief setting if the trencher motor is not turning. Reverse the direction and gauge should drop to original charge pressure.

 

[r8f1k]

One thing that I have done as of today, is I changed all the filters on the machine, topped off the fluids and checked to see if there is any change. So far, none. However, I cracked the hydraulic line that runs to the hydraulic drive motor and turned on the trenching chain. NO REAL PRESSURE change at the motor. Is it possible that the pump is no good OR is it in RELIEF? I can hear it sort of 'engage' and chatter a little. There are a couple relief valves on the side of the pump, could they be loaded with trash? If not that, is it smart to pull the pump, take it apart, clean it and try again? How hard are piston hydraulic pumps to rebuild?

 

[oldnslo]

R8
Silly question but with fitting loose at the motor did you try operating in both directions?

Is the chatter you hear coming from the pump area? Can you feel the pump case to see if it gets warm or hot quickly when trying to operate? Does it chatter in both directions?

The relief valves are probably work port reliefs for forward or reverse so if chatters in both directions doubtful would be relief valves but anything is possible.


Dismantling and repairing piston pumps complexity varies with different manufacturers and control style. Main thing in cleanliness when reassembling.

 

[r8f1k]

I did try both directions, no change.

Chatter comes right from the pump. I don't run it too long, afraid to burn up what I already have. Chatters in both directions, not louder in one way or the other.

I'll pull the relief valves out and give them a wipe down.

Never pulled apart a hydraulic pump, not sure how to order new 'generic' parts which I assume is something you can do. I am a high school auto shop teacher and I have tore into lots of engines, transmissions, etc. and unusually you can buy generic bearings, seals, pistons, rings, valves, accumulators, etc. once you have measurements. Is there such a thing for hydraulic pumps? If so any good websites to order?

 

[oldnslo]

Seals and bearings should be standard sizes but the rotating group or pistons and cylinder barrel assembly are specific to a manufacturer. If you can find a make and model then parts should be easier to source. I will do some digging through my old stuff to see if I can find some service info for Eaton - Vickers products.

 

[r8f1k]

Thank you!!!!! I appreciate the help!!!!!

The pump I have has a tag on it:
18-2081R LH
87-11-80260

I think it is Case part number:
H672705

 

[oldnslo]

R8,
attached is parts break down on a Sauer Sunstrand (now Danfoss) series 40 pump. This will hopefully provide a visual aide in how these model pump is assembled. Other brands would probably be similar but none of the rotating group would interchange.

Hope this helps Vs hinders

 

[r8f1k]

I'm pretty sure that the pump that is in this machine is a gerotor type pump, anyone know where to get generic parts for a pump like that? I'm going to pull it out next week. I took the rear trencher boom off, trenching chain, etc. I need to rebuild the hydraulic cylinder that lifts the trencher, so I took all that off to make it easier.

 

[oldnslo]

R8
Are you talking about the hydraulic motor on the trencher or the pump being driven by the engine?

 

[r8f1k]

I'm talking about the hydraulic pump that is driven by the engine. I'm sure I can come up with generic o-rings, gaskets, but not the gerotor assembly.