Please help, we have a Hitachi 870 Digger making noise in the pump drive area. We cut open the big filters from the hydraulic tank and found small traces of metal. Management suggested to change all 4 hydraulic pumps. New pumps were fitted but the noise is still there slightly worse than what it was before the pumps change out.This machine has 12000 hrs and the pump drive has never been replaced or repaired. We are not sure if the pump drive might be causing this.
Did you disassemble the pumps to check for any internal issues? Was the pump drain filter also cut open to check for any contamination? The pump drain filter generally gives a better idea of pump condition because the tank return filter catches metal from the whole system. the drain filter only gets contamination from the pumps. Also, the pump transmissions on the large size machines, 670/870 etc do tend to be noisy at idle. I've actually increased the idle rpm on some 870's by around 50 rpm to quieten them down slightly. Does the noise improve as the rpm is increased or the pump load is increased? Also, has the pump transmission oil been changed to check for debris? And what oil is running in the transmission?
there is a drive coupling that tales off shocks that comes from the engine. I think they need to replaced
As mentioned above pump case drain filter is the go to filter for pump problems. Can you describe the noise? A hum would usually be fluid flow related. Clunking and knocking would likely be more of a mechanical issues. I can't say I've seen an 850 or 870 pump drive fail catastrophically but I have rebuilt a couple during midlife tear downs. Pump drive to engine coupler. Trying to remember (been like 5 years since I last saw one). I think they're just a plastic or nylon type ring that's bolted to the engine flywheel. Male end of the coupler is steel and installed on the pump drive input. They do strip out and fail once they get too much wear on them. I always highly recommend replacing it when the pump drive gets removed simply due to the labour and downtime involved in replacement.