Case DH4B Trencher/Backhoe Won't Spin Trenching Chain

[oldnslo]

R8
Can you post some pictures of the pump in question. Reason for asking is that some piston pumps have a geroler style charge pump.

Another question, how many hoses are connected to the pump in question?

 

[Doaaj50]

A picture of the name tag would be super helpful, if available.

 

[r8f1k]

(DH4B) - CASE TRENCHER (1/79-12/91) (8-206) - ATTACHMENT DRIVE PUMP - H672705 Case Constructuion

spare.avspart.com

99% sure it is this pump

 

[r8f1k]

Not sure if this photo is coming up.....

 

[oldnslo]

(DH4B) - CASE TRENCHER (1/79-12/91) (8-206) - ATTACHMENT DRIVE PUMP - H672705 Case Constructuion

spare.avspart.com

99% sure it is this pump

That parts diagram is a closed loop (hydrostat) pump with a geroler style charge pump. The only components that could be generic are seals and bearings. None of the internal oil moving components will be generic.

Has this unit ever worked or did you buy it in this condition?

I would suggest performing some pressure tests before condemning that pump.

Is charge pump getting flow and building pressure?

how is the pump driven? Is something slipping or wore out in the drive couplings, splines, etc. ?

 

[r8f1k]

I bought the machine dead. Did not run, didn't even crank over. From the dates written on the filters, late 2009 was the last oil change. I'm betting it was last really used sometime after that, say 2010-2011. It has 3 total pumps, 1 drives the propulsion, the other 2 operate the backhoe and the trencher. I am going to pull the pump out, and take a good look.

I will check to make sure that the pump is getting a full flow of fluid, but I'm betting that there is something more involved going on. I drained as much fluid as I could prior to the initial startup to prevent any old debris from getting recirculated in the system.

This pump is driven off of a drive plate with 3 splined holes. Each hole has internal splines and drives one of the pumps. This pump is all the way over to the right, although labeled as the LH pump. It could have worn out splines or something like that. I think the only way to really find out is to pull it out and take a look. Even if I don't take the pump apart, I should probably take a look at the drive splines. I will check the fluid flow going to it, but I am betting there is plenty of fluid, although the line could be plugged???? Worth a check before pulling it.

 

[oldnslo]

Do the spline couplings run in an oil bath or dry? If dry couplings have been known to fail due to fretting. Slipping splines could cause the chatter you are hearing while attempting to operate in either direction..

 

[r8f1k]

I am not sure......I can see some RTV where someone was in between the engine and the drive plate. Maybe it had an issue already. Lets just say the splines are worn, if they are worn off of the input shaft of the pump, what should/can be done? If they are the splines on in the inside that are worn, what then? I am guessing that a pump input shaft is easier to repair where a machine shop can index new splines.

 

[Doaaj50]

So what you have on that machine is an old Sauer-Sundstrand 18 Series pump. The model number is 18-2081. For Sundstrand/Danfoss, anytime you see a "R" at the end of a model number, it indicates that it has been remanufactured.

The "LH" indicates that it is a Left Hand rotation pump (counter-clockwise). If the pump was sitting in front of you with its input shaft facing you, the shaft would need to rotate to the left, or counterclockwise.

Since we know that it is an 18 Series pump, we also now know that it is a closed circuit system. Oldnslo had already mentioned that based on the exploded view diagram.

Based on what you have described so far, my first thought would be to check for charge pressure. I believe oldnslo has also mentioned that in one of his posts. The problem with a direct displacement pump, is that you can force it into stroke without charge pressure. Without any charge flow, there is no oil in the circuit to send from the pump's rotating kit to the motor and thus no trencher chain movement.

The noise that you are hearing from the pump could be the charge pump running without any oil. If that has been going on for a while, then you may have an issue because those parts rely on an oil film to keep them from damage.

I would first start by making sure you have oil getting to the inlet of that pump. The inlet of that pump can be found on the diagram that is attached.

I would crack that hose fitting at the pump and see if oil is reaching the pump. If not, you will need to backtrack it to figure out where the obstruction lies. There may be a suction filter or screen that is plugged.

If you have oil at the inlet, then get a 500psi gauge and plumb it into the charge pressure gauge port and see what pressure, if any, the pump has when the engine is running. It should be at least ~100 psi. Some of the 18 series pumps ran fairly low relief settings so don't be surprised if it is at that level. It may be higher, but it shouldn't be lower than that.

In case you are not familiar with a closed circuit system, here is a system that should be similar to the one that is on your trencher.

Keep us posted on how your investigation goes. We can help direct you based on your findings.

 

[r8f1k]

Ok, I can see if there is oil heading down to that part of the pump. HOWEVER, right now I have no oil in the machine at all. I am swapping the excavator controls for a 2 joystick control and there was a lot of water in the system. I am opening all the lines I can find at the lowest points to drain out any water, old fluid. It looks like it had ATF and everything is PINK in the system, so my bet is there was plenty of water in the system and all the fluid is/was contaminated. I have all new filters and new fluid, but I also want to pull the hydraulic tank out and give it a rinse in my solvent tank to get any trash that might be in it. Since there are so many lines on this thing, any advice for purging out old oil without wasting a bunch of new? I thought about putting an air line on it and blowing the system out. The lowest lines have been dripping for days and have rendered about 5 gallons of oil/slime/water.

It is a distinct possibility that the oil tank is full of trash and the line is plugged going to the pump. I ran the pump in one direction or the other for not more than 10 seconds. Each time I tried an separate occasions (4 times), the chain would barely move.

The only thing I have no real experience with is getting a pressure gauge in line. Any recommendations on what to buy and where from?