We've been working on resurrecting a 1989 Link Belt LS4300 CII (Sumitomo-built) excavator for almost a year now and have gone through and corrected almost every imaginable problem, all ultimately fixed but now down to the original problem of NO TRAVEL. We're running in by-pass mode since the original controller was long gone. We've fabricated a new switch console and assigned a dedicated switch to each of the 10 solenoids in our machine. The proportion valve is powered using the original resistor to limit current per the wiring factory diagram and have all manuals and key sheets for this machine. We also rebuilt the pump with a new pilot pump and bearings. Pilot pressure is at around 600 psi and main pump pressures were within expected ranges until after reassembly. I suspect that previous attempts to get the machine going might have included adjusting the pump regulator or control valve adjustments. The bad bearings in the pump were the reason why we took out two new pilot pumps within 10 minutes until we finally understood what was going on with #2 pump gear wobble from the worn bearings, likely caused by a low oil event experienced by the previous operator. Inspection during the tear down and bearing replacement showed no evidence of significant metallic contamination, and neither did the hydraulic tank when we thoroughly cleaned it and inspected the filters. We have good pilot pressure now, though pumps #1 and #2 are showing less pressure than prior to the bearing replacement. We have swing, boom, arm, and bucket control though perhaps slower than normal, but travel is nada. The rotating joint had been resealed prior to our getting the machine. We have reached a point despite learning so much about the workings that we need to call in some help with enough experience to help us diagnose and correct this last problem of no travel. Testing the control valve operation and pressure adjustments on the pump is where we're presently stumped. It's located on property just south of Colfax CA, about halfway between Reno and Sacramento, and 45 miles on paved road from Sacramento. If you or a reference can help we can really use the outside assist. Thanks, -Tom
Have you done a pressure test on the drive motors or done a casedrain flow check on them?
To be completely honest, that's where we're getting bogged down. The machine traveled maybe 800 feet to its present location after other problems sidelined it from operation. It had been run with low oil pressure when the boom and arm functions began to fail. The cause was almost certainly the pilot pump failing because of gear drive wobble from the pump shaft #2. It was likely going out slowly, and exacerbated by the pressurized oil running low because of an ignored slow oil leak. We've installed a relief valve at the pressure gauge now and take the air pressure off the hydraulic operation after running. I think at this point I need to bring in someone more experienced with diagnosing the problem. We've been at this for so long that to hit another head scratchier just doesn't make sense. And resealing the leaking oil cooler that was deemed in need of replacement was just the latest chapter in this story. But we did it! A fresh diagnoses from someone who knows this pile of iron is presently the quickest way for us to breathing life back into the beast!
The pump #2 pressure (for travel) used to jump to around 4500 psi prior to the bearing replacement when travel is initiated but now is around 1100 psi. The pump was properly assembled and checked during the bearing replacement and the regulator block on the side of the pump was inspected for any sign of metallic contamination. None found. Clearances for the pump shafts are in the spec'd range and the pistons and barrels for pump #1 an #2 look perfect.
Related story,I found and saved a long parked Link-belt 2800C excavator couple years ago,pumps were a bit tired,everything worked except the arm/stick in out function,turned out it was the plunger spools on the pilot control valves for the joystick itself.They pushed in,but some corrosion would not allow them to return,it created an open type circuit and didn't function,took apart,lubed,cleaned,all was well.Here's hoping your pedal valve in the floor maybe stuck the poppet/spool valves closed.The spring still gives a return like feel in the lever,so was hard to diagnose.Probably not your issue,but would be cool if it was that easy.
Great tip and much appreciated. We see the pilot pressure jump when trying to engage travel but no discernible action from either travel motor. Thanks, -Tom
I met with the previous owner yesterday and got a vital clue. When last working in early 2011 swing and boom were getting weak so he walked it over to the shop area about 300 yards from the work site. He made it about halfway when the travel began to stall. They checked hydraulic oil and found it extremely low. They added about 20 gallons and got it over to where it has been for last 9 years. When parked it was thought that the problem was a leaking rotating joint, so they removed it and had it resealed before re-installing. The work in 2011 was assisted by two junkies who installed the hoses, and after that it has not had travel after we rebuilt the pump (bad bearings that kept taking out new pilot pumps for us), and have wracked our brains about why there is so much bypass from the travel motors with no movement. We have corrected many previously existing problems and now have all functions working except the travel. I'll start a new thread for the followup but if anyone has either a diagram or other guide to the correct hose routing on the rotating joint that will save us the manual work of tracking the hoses and seeing where they're presently connected on the rotating joint it would be most appreciated. As always many thanks to you folks who've guided us along in ressurection of this long-abandoned beast!