L555 hyraulic problems boom

[agb1758c]

I have a older L555 (SN624325), the boom would slowly raise in the lowering pedal position and lower in the raise position. While working on it and testing the hydraulics the aluminum gear housing on the small hydraulic pump split. Prior to the housing split, I had replaced both filters, clean screen filter and drained and replaced hydraulic fluid. What would cause the pedals to reverse their function? Could the control valve bypassing cause this? I am figuring the housing split from wear or could it be from over pressuring? Machine has approx 3600 hrs on it and because of work injury it has been sitting 1 1/2yrs. Any suggestions and help would be greatly appreciated, never know how much you miss these machines until they breakdown.

 

[Mike10]

The pump failed because of pressure. Unless you somehow by-passed the control valve relief valve when testing you should always replace the relief valve when a pump splits. Is your bucket foot control centering the control valve spool. If you are building pressure in the oil return circuit it will cause your boom to act the way you say yours is. You might try and install a pressure gauge on the oil return line. There willl be some pressure present because of the check valve for the hydrostat charge pressure. You should be able to remove the charge pressure sender back by the filters and install your gauge there. Have there been any external valves or hyd controls added to the machine? The only other thing I can think of is if the oil cooler is blocked so there is no where for the return oil to go. This will cause high return pressure but I don't think the cooler could stand system pressure without bursting.

 

[agb1758c]

The pump failed because of pressure. Unless you somehow by-passed the control valve relief valve when testing you should always replace the relief valve when a pump splits. Is your bucket foot control centering the control valve spool. If you are building pressure in the oil return circuit it will cause your boom to act the way you say yours is. You might try and install a pressure gauge on the oil return line. There willl be some pressure present because of the check valve for the hydrostat charge pressure. You should be able to remove the charge pressure sender back by the filters and install your gauge there. Have there been any external valves or hyd controls added to the machine? The only other thing I can think of is if the oil cooler is blocked so there is no where for the return oil to go. This will cause high return pressure but I don't think the cooler could stand system pressure without bursting.

Thanks for the reply, currently I'm locating a new pump gear housing, will be next week before I can get to hydraulic shop. I will also check on the pressure relief valve and replace. Will get back when I have pump on and gauge put on to test pressure.