YM 155D Hydraulic Problems

[digger57]

I could use a little help sorting out sudden loss of hydraulic pressure to loader and backhoe. I was digging with the hoe and hit a stump and experienced loss of almost all hydraulic lift to the hoe and loader. I removed the pump and visually it looked ok - nothing sheared or cracked. It turned free. No leaks. It pumped when primed on the bench. I changed fluid (it was milky) and cleaned the screen. I checked the valve (by the 3pt hitch lift); there is also an adjustable valve near the fender - removed. cleanded and replaced but I couldn't get the plunger out. Both implements do not work; the 155 has an A/B switch for the loader and hoe and both ways do not work so I'm guessing the problem is up in the pump or diverter block area. The three point appears to work ok. Are there check valves elsewhere in the system - in the diverter block? It is acting like a relief valve is stuck open but the diverter block plumbing baffles me. I'm probably getting about 50lbs of pressure at the implements at high rpms; just enough to move them a little. Thanks to anyone who can steer me in the right direction.

 

[digger57]

Problem solved. I am posting this in case someone else has similar problems. I deduced that the problem was before the distribution block because both the hoe and FEL were weak when I switched to them using the A/B switch. There is no pressure release on the Yanmar between the pump and distribution block; instead, each hydraulic circuit has its own pressure release. Therefore, the pump had to be the problem. (not happy about that). I opened the pump to look for cracks or wear etc and found that the internal o-ring seal under the drive gear had failed. I was able to find replacement in my o-ring assortment and was back in business. Pretty simple repair once it was diagnosed.