I have a komatsu wa320 loader and the bucket dump cylinder bleeds down it will do it slightly when empty but when loaded you have to hold the dump lever or ot will bleed off and dump your load. The cylinder did leak some out of the end but had it rebuilt and still the same. Has anyone ever seen anything like this before. I don't have a hydraulic schematic for this machine. Thanks in advance
Simple test, start cold, after you've warmed up the engine. Grab a pile of material, raise and hold the load in the air. Hold the position for a few minutes. Dump the load , back away and park safely. Crawl up and put your hand on the tilt cylinder, if its warm or hot, you're gonna want to get it repacked properly. I apologize if this sounds oversimplified, I just don't know your skill level. The heat is an indicator of a leak. The idea is that a cylinder will not generate heat in a static position if it isn't leaking. Good luck and please report back.
Please don't take offense about the next sentence. The information you have provided sounds like this. I have a car, it's black and has an engine. What is it worth? No one can help with much if you don't provide at least the basics of information. Year of manufacture, serial number, hour meter readings and maybe the kind of work the machine is used for are all very important questions any competent mechanic would ask you before jumping into troubleshooting your problem.