I have a JD 310 SE that has lost power to most of the functions. Front bucket will not lift or curl with out throttle applied, more throttle more speed. Same with rear boom and down-riggers. The steering is also effected and only with full throttle or driving the machine will it steer. I just happen to realize when messing with controls that if I hold front bucket to either side for curl while trying to raise the rear boom it works fine but release the curl control the rear boom stops and again only throttle will make it slowly lift. This also happened 6 months ago and we took it to a hydraulic shop, the replaced the bottom section of the loader control valve and the valve body at the rear for the backhoe. The top two sections are no longer available from JD we have been told. We ran the machine for about 6 months and out of no where the problem came right back. I seen on another post about an orifice that falls out and makes the same problems, Im wondering if this is our problem. BUT the post with the JD bulletin said steering is not effected. Also when they replaced the bottom section of the loader control valve the spool with orifice should have been new.. Maybe they put the old one back in I dont know. Anyone have any thoughts on this I would appreciate it. We also replaced the hyd pump!
If your relief valve looks like the one in the parts picture replace it with the updated relief.