Case DH4B Trencher/Backhoe Won't Spin Trenching Chain

[r8f1k]

(DH4B) - CASE TRENCHER (1/79-12/91) (08) - HYDRAULICS Case Constructuion

spare.avspart.com

Here is a link to the hydraulic schematics. It shows a selector valve, but I'm not sure how it is plumbed based on the drawing.

 

[r8f1k]

I should add that my machine is a FRONT BACKHOE, FRONT BACKFILL BLADE and REAR TRENCHER with steering wheel and 2 seats, one seat forward for the backhoe and one for driving and the trencher.

 

[Doaaj50]

It would be helpful if you could take a picture of the other 2 pumps so that we can identify what they are which will help us figure out what each one of them are doing.

My assumption is that you have this architecture on this machine:
1. One open circuit pump that controls the cylinder function for the backhoe and the trencher lift cylinders.
2. One closed circuit pump for the propel of the machine
3. One closed circuit pump for the trencher chain operation (this has already been verified and is the pump we have been discussing)

Back to the trencher chain circuit, can you trace the high pressure lines from the pump and find out what they are attached to? There are two of them, they are on opposite sides of the pump. I have highlighted one of them on the attached picture. The other one would be located on the opposite side of the pump.

 

[Doaaj50]

Doaaj50,
Since you sound far more familiar with this Sauer unit would both control shaft rotate if the pins was missing on the side being driven?

Does this model have work port relief valves? Just curious since I know some Eaton units had the reliefs in the motor.

If major leak would he see charge pressure or would it drop?

oldnslo, here are my responses...

1. There are two trunion shafts on this pump, so theoretically if you rotate one and see the opposite side rotate, then you can rule out the pins being displaced.

2. This pump has high pressure relief valves so it is safe to run it in a "dead head" condition.

3. I am following your question logic on this one. I should have been more specific before, it is acting more like a short circuit condition where the high and low pressure loops are connected somehow that is causing the motor not to rotate. The fact that charge pressure is stable leads me to believe it may be more of a hose connection issue instead of a mechanical issue inside the pump or motor. Typically when you have a rotating kit failure you end up with charge pressure dropping as well. The only other internal failure I can think of that could cause this sort of behavior might be a failed endcap casting that is allowing the oil to freely flow between the high and low pressure loops.

 

[oldnslo]

3. I am following your question logic on this one. I should have been more specific before, it is acting more like a short circuit condition where the high and low pressure loops are connected somehow that is causing the motor not to rotate. The fact that charge pressure is stable leads me to believe it may be more of a hose connection issue instead of a mechanical issue inside the pump or motor. Typically when you have a rotating kit failure you end up with charge pressure dropping as well. The only other internal failure I can think of that could cause this sort of behavior might be a failed endcap casting that is allowing the oil to freely flow between the high and low pressure loops.

I agree it does sound like either a plumbing issue or the motor is spinning but not engaged into the trencher chain drive. If I recall correctly R8 stated the chain would try to move and then their was a lot of chattering. Now stating no movement and no noise so something has changed. Question would a motor spinning freely not build any pressure. I would expect frictional and line losses to show some pressure change.

 

[oldnslo]

So, my assumption is that the pumps operate a number of things, but can't do it all at the same time. There is NO DIVERTER valve. Was it removed? I have no idea. Perhaps someone declared the trencher 'dead' and decided that it could just be used as an excavator and took hydraulics out? The backfill blade has a 3 spool control, none of the controls do anything, but the lift trencher lift cylinder does work and it is plumbed on that same side. If a diverter valve is missing, where would it pull hydraulic pressure from? The left hand side pump? If so, then I assume you are splitting from backfill to trencher lift cylinder. However, I still have the issue of the trencher motor/pump. Is there a way to test the motor in place?

I looked at schematic and the trencher is the only item that should be connected to the pump in question. The blade is driven from a different pump suspect the gear pump.

 

[r8f1k]

I think I have a plumbing issue......I'll get some photos and send out a 'path' of what is happening

 

[r8f1k]

I am not with the machine, but I will give an update as to what I think is there. If the backfill blade is operated by the same pump as the trencher lift cylinder, they do not share the same return or feed line. The return line is connected to the trencher chain MOTOR. It is hard to see, but I am pretty sure that is how it is plumbed. If that is the case, is the trencher chain pump being 'dead headed' and only getting oil one way? Is there no 'loop'? It will take me a little bit to sort this out some more, but I will get photos of the unit on Monday. There is an access panel behind the chain boom and I have the boom off, so it won't be too bad to get in there. On 2-10-23, I ran the unit outside and tried to get it to do more operations than before, status quo. I know it needs more oil, but I think I may have a plumbing issue if the backfill blade is supposed to be driven off the same pump as the excavator. I think once that gets sorted, the chain drive issue may reveal itself. Perhaps someone swap hoses and condemned the machine?

 

[r8f1k]

Ok, I filled up the hydraulic system all the way and still no change. No backfill blade and no trencher spinning. What I find odd, is the backfill blade still doesn't work. It shares the pressure line that feeds the trencher lift cylinder. The pressure line splits before both control spools, the trencher lift cylinder works great. The blade has pressure if I crack the line, but nothing moves or even groans.

I will add a photo of the trencher motor, if memory serves, there is a port on the side where you can add a gauge.

 

[laurencen]

long shot but has the spool stuck or rusted in the valve? can you take the caps off and move the spool?

 

[r8f1k]

Not sure. I have not pulled the spool apart. All the levers move, but I have not pulled the valve cap. Is it possible that the same thing is wrong with the trencher? Could that spool have a stuck valve? Or is that a different style valve?

 

[laurencen]

I have seen where the spool floats in the valve, the spool can stick in which case it does not move with the levers or not full stroke

 

[MTGreen]

Did you check to see if the relief valve is stuck open

 

[r8f1k]

Here are the photos of the spool in question. Here is a list of the problems I have found.
1) When used, NOTHING happens. Another user indicated that the spool might be plugged up or stuck. I began pulling the unit out and I saw something odd. All of the OLD fluid in the machine was RED. All of the NEW fluid is CLEAR. When I disconnected the lines that went to the cylinders, only RED fluid came out. When I pulled 'IN' hose, clear came out. That narrows it down to it having a blockage of some kind.

2) Pulled the spool out, tried to cycle through all three functions with air, not much happens. If I put air into the 'IN', and I cycle the spool closest to the 'BYD' port, SOMETIMES air will come out of the top port. I'm not sure what to do to clean it out. Any help on that would be great. Given that some of the fittings are RUSTY, how do you get them out?

3) One strange thing that I have a feeling about is the 'BYD' port. I can't get fluid or air to come out of the 'OUT'. There is only flow through the 'BYD' or 'IN' ports. If that is the case, the 'OUT' port has a hose going right to the trencher MOTOR. If this spool is blocked, could that mean that the motor will not work without a proper path of fluid? Is this the hang up with the whole trencher?!!!

 

[oldnslo]

There should not be any directional valves in the trencher motor circuit if it is being driven by the Sunstrand hydrostatic pump we have discussed in previous posts.



Depending on trencher motor style they might have run some tank line flow through the trencher motor case for cooling and flushing. Not common practice but possible.

 

[r8f1k]

Did you check to see if the relief valve is stuck open

Which relief valve, I do not know how to identify a/the relief valve

 

[r8f1k]

Does anyone have a recommendation for cleaning or clearing out a spool like this? Replacement is going to be difficult given that it sits down inside of the side of the excavator. Most newer spools have levers mounted much closer to the body itself. This unit has levers that sit 'higher' up. I'm not opposed to rebuilding the unit, I just don't know where to start......I don't really want to heat the unit up to get out the large flathead screws on top, but I guess if I have to, someone will chime in.

 

[oldnslo]

R8
Do all the spools move when you move the levers? If yes then the only repair would be seals on the ends under the covers and clean the centering spring mechanism.

On the rusted screw plugs. Remove one of the hose fittings and look down inside the port. I suspect those just may be plugs in auxiliary ports.

 

[r8f1k]

I don't think they always move. I have them soaking right now in my solvent tank. I will test again today with air and report.

 

[laurencen]

would those large screws above spool be pressure relief or restrictors to slow movement? I would take lots of pictures and take it all apart, soak in Diesel for a couple days, brass brush to remove gunk, use a brass bore brush in the valve body, thinking its totally gummed up inside