We've been chasing down a remaining problem of low pilot pressure on our machine, so after assuming that the pilot pump was okay we spent lots of time thinking that the pressure was being dumped somewhere after the pilot filter. Finding tht the the solenoid control valve was working properly and not bypassing to the tank we finally capped off the pilot oil line where is connects to the pilot filter and installed a test port. We found that pressure cold at idle was around 200 psi, but dropped to around 40 psi when the fluid warmed to around 100 degrees F. I pulled the pressure adjust cartridge off the front left side of the pump to ensure that it was working properly, and tried adjusting it in and out with no change in pressure readings. Prior to our getting it a few months ago it sat for over six years, apparently because of this and other issues that we've already addressed. As I understand it the rotary joint had an O ring failure that caused loss of fluid and lack of travel motor operation on one side. The previous operator put in enough fluid to move it about 350 yards over to where is sits now. The first thing I did was to inspect the filters on the machine all around and add about 40 gallons of new fluid. No debris or contamination was found in the filters or lines, and these had been replaced by previous owner less than 200 operating hours prior. As it stands it appears that the pilot pump section has an issue. Pump sections #1 and #2 are putting out around 5000 psi at high RPMs and appear to be fine. The only motion we currently get is VERY SLOW arm, boom, and bucket with high RPMs, and no travel or swing (though the motor slightly lugs as though trying). Our assumption is that the low pilot pressure is insufficient and unable to fully move the control valves for proper operation. So now the question is to confirm that our test of pilot pressure with the blinded pilot pressure line was proper and that we haven't missed something obvious, and whether we can do a field repair or not. The machine is off the grid on our adjacent mining property, an level and clear hard ground. Pulling the pump is not a major issue for us as we have our excavator to assist with handling the 260 lb weight of the pump assembly. The messiest problem is draining and storing the hydraulic tank oil prior, and that should be relatively easy with a clean 55 gallon drum to transfer the oil into. Since we're in the Northern California Motherlode region finding anyone familiar with the Uchida A8V pump is the challenge. Neither of the LBX service managers I've talked with have any knowledge of the inner workings of these "older" pumps. I have sent a message to several West Coast shops that deal with service and rebuilding, but haven't heard anything back as yet. Any thoughts or comments would be most welcome. Thanks, -Tom
Good day lowahill May I suggest that you test the pilot pressure with fluid at working temperature, at both idle speed and full revolutions - a pressure value at high rev's should not deviate so much and low rev's if that is the case you have a severe circuit leakage - could be a worn pump or leaking down line - from your thread you have taken the best approach to plug possible leaks. If the machine has worked in access of 5000 hrs it is fair to assume that your pilot pump is up for a holiday.You can down load information go excatech.org - library - GI checking servo pressure Kind regards Uffex
Most appreciated! I believe after all the testing we've done (both cold and with fluid warmed up to over 150 degrees F) we saw no change other than lower pressures than when cold, that we have a pump issue. So now the question boils down to if we can pull and repair JUST the pilot pump section since it's at the front of the pump. And yes, this machine is likely over 3-4 K of operating hours, though the Hobbs meter is missing. The motor, undercarriage and other hydraulics look good, and it seems to have been properly serviced with filters and lube. But like so many of these older units it's been pushed hard.
Good day Lowahill Whilst I can appreciate you have used the temperature span to measure the pressure please do to miss the point - a fixed displacement pump will maintain the pressure level at full speed however at low revolutions the pump flow & pressure reduce, any significant loss of flow will show that significant leakage - example full revs = correct pressure value - Idle engine speed = significant drop in pressure, indicating loss of flow to maintain the pressure. Maybe you have this point covered to your satisfaction good luck to you. Kind regards Uffex
Thank you again for your input, Uffex. At full revs we still don't get above around 200 psi when cold, and it drops to less than 100 psi when warm (again at high revs). We initially thought that the pressure was being dumped back to the tank somewhere, having assumed that the pump pressures were fine when it was moved and parked prior to our getting it. But it's looking more like something more serious and requiring removal of the pump UNLESS another possibility exists that we're not aware of yet. As I understand, the pilot pump is a gear pump with fixed displacement, and the pressure relief to the tank is achieved with the valve cartridge on the left front of the pump housing. An aftermarket Sun Hydraulics relief valve has been installed in the relief line that connects to the pump intake end, likely as either a cheap fix for a bad original valve or as a backup in series. But here is where any uncertainty on my part comes into play due to my unfamiliarity with the pump internals, such as some internal valving that might be malfunctioning. Your helpful insights are gratefully appreciated.
These guys used to repair a lot of these pumps. http://hydraulicrepair.net The original C model pumps were different than the C 2 models but worked the same way. The C and C 2 model machines were popular loggers in their day. As I recall, it took at least 600 PSI pilot pressure to make all the systems work properly on those machines.
If theses are the folks up in Puyallup Wa I've already sent a message to them. I think I've seen more examples of the LS4300 version of the Sumitomo related to logging. I'm hoping that the job will be made easier and cheaper if I can pull the front pilot gear pump section without disturbing the #1 and #6 high pressure sections and either reseal and replace in my own shop without having to ship it off. Fingers crossed!
Why don't you try calling them instead of sending texts and emails? Most of the repair places now days are just ignoring that kind of communication. In most cases a text will go to the equivalent of a dead letter number that no one ever sees. Gear pumps that have lost efficiency usually have damage to the gears, center section or the end plates. Another thought to consider is the drive coupling between the engine and pump. It is the dry type that uses biscuits to smooth over the torsional vibrations. In my experience they are usually trash by the time you pull out a pump.
As I only saw the web site early Saturday morning before the roosters were up I saw the link that reads "Contact Us". So I did and gave a description of what our issue is. When they open Monday I'll call and see if they got my information. I'm certain we'll have a complete view of issues when we pull the pump and tear it down. Thank you for the input! -Tom