Hey hef I got one of them can you fix my machine but I can't stop running it and it doesn't always act up kinda jobs and I'm hoping for some advice. Machine was digging for a few hours no complaints operator says all functions stop he cycles safety lever few times and it starts working. Now when machine swings it interment stops then will swing again after a few minutes pause or by bumping another control. over the past two days it will do this on stick,boom, or travel only seems to act up on one fuction at a time .but if you change direction and retry function it will work. it seems to be worse as the day goes on when a function doest work the whole pilot pressure system drops to around 200 psi and doesn't recover until another functions is activated or original function is reversed. Any thoughts welcome this is the first time I'm working on Komatsu hydraulics and theory and terminology is a little different from my previous experience
Also I took pilot pressure at main control valve for swing left and pilot pressure at ls-epc very little change between betweeen the 2 l. no load pressure pilot is about 425psi and full load is around 800psi I inspected self reducing valves relief and seems to be in working order the ls-epc changes with work mode.
I think that pilot pressure should always be 425 PSI at any load. I think checking the cheap stuff should be the next item. Filters would be the place to start. Almost sounds like you have a floater working it way through the circuits. I haven't had the pleasure on putting my hands on one of those models. Does it have an electric pilot shut off are a manual valve?
that should have high pressure screens on the output lines of the pump, cehck them for debris.. ive seen pumps wear out so bad that no metal shows up but the pump swashes back to nearly 0 output and is not enough to make pilot oil. all the -6's i have seen have a seperate pilot pump off the back of the rear pump, those have filters in them when you pull the fitting off the top right side and unscrew the filter out.. should have an epc under the control valve for the pilot circuit, you could try swapping the coil and stem with the 2 speed travel. could have a coil getting hot and cutting out... also check to make sure all the pressure swtiches are wokring by leaving it at hfi and have auto decel on,then when idle kicks down hit each function and check that it idles up and then down again, the swing issue could be the swing brake coming on beacuse its not seeing presure on the switch telling controller to keep going
Thanks for the help john c and dk88 this is what I found today both high pressure filters were split length ways just to out screen only few small pieces broke off. Strainer on top of return filter had about soda cap full of black soft rubber like the ring under piston seal in a cylinder few pieces of metal and pieces of high pressure screen return filter had pretty much nothing when cut apart. Relief valve in self reducing valve for pilots was binding after lil polishing I got pilot pressure set to 410 ish psi. Fuctions seem normal with proper pilot pressure except for boom raise still is really slow with stick out but seems to load engine about as much as other functions. So I cleaned and inspected relief valve seems to be in working order hopefully adjustment with raise lift pressure it's only building 3000 psi at relief.
Also it has ball valve pilot shut off. And all pressure switches seem to be operating. Each function cancels auto idle down.
The rubbering stuff in the filters sound a bit like cylinder packing. Is there any drift down in the boom function?
No drift in boom I resealed boom cylinders a month ago but the day before first complaints we in stalled a used bucket cylinder. I tired uploading pics with no success from my phone. Is it easier to upload photos from a computer?
The ball valve is actually for cold weather start up so oil can circulate to generate heat.
The ball valve was to unload the hydraulics so the starter wasn't pumping oil under pressure while trying to turn the engine fast enough to start. A funny aside about that was that the loggers on wet days would store their rain gear in the pump compartment to warm up and maybe dry out at lunch time. They would pull it out to go back to work and move that lever about half way. I got lots of phone calls in the middle of the day complaining that the machine ran great but after lunch it wouldn't get out of its own way. Sounds like some junk in you system might be causing you symptoms.
For the heck of it, warm up the hyd's and paint one pad on each track, jack up left track and full throttle h/o mode, auto decel off and spin the track and see how long it takes to rotate 5 times once it's already spinning, in each of the 3 travel speeds and repeat for the right track and let me know the readings, I'm wondering if one pump is a little lazier than the other.. All your doing is a quick and easy flow test for pumps, each track uses one pump but boom up and arm out should merge the pumps, I can't seem to remember if that one has a boom high or arm high valves..
Update i found some junk in relief valves and they were pretty scored. After changing both main and boom up two stage relief valve and adjusting them I can build 5000 psi on both pumps and main reliefs And if I boom up and lightly press a travel pedal I can build 5000 psi but if I straight boom up I can only build 4750 psi and I'm not sure where the pressure bleed off is. I think boom lock can dump to tank but that should affect combined flow or not.maybe I have a problem in combined flow valve section? I need to check what stick in relief is . @dk88 I was going to check track speeds but once the machine was usable they wanted to run.
Travel runs at a higher pressure than the implements. The two stage relief opens at 4,750 in normal mode and when you operate travel or press the power up button on the joy stick pilot pressure is introduced to the relief which ups the pressure. The power up function is timed for about seven seconds and then stops. Here's a secret about the two stage relief that most of the Komatsu people won't tell you. Set the swing brake and you get the higher pressure all the time. The boom lock valve has a circuit relief. If it leaks the boom will drive down all the time.
I don't think that there is a pilot pressure that flows to relief valves to make the two stage. It is more electrically done as a cut-off function on pump
The gentleman stated he changed a two stage relief? I don't know of any relief valve that has the ability to change pressure settings electrically. I haven't worked on a Dash 400-6 model but seem to recall looking at one in the past. I recall the system was still using the Dash 5 OLSS system. Is this correct or did it go to the CLSS system?
every komatsu I have seen that has a 2 stage relief does it with a pilot supply.. from -6 to -11 excavators
The PC400-6 uses CLSS. And the 30 tons class and 40 tons class of dash 6 have two relief valves, one on top of each side cover of main control valve. These particular models didn't have a pilot hose flowing to relief valves, unless I am wrong. The first stage is 325kg/cm2 and the second 355kg/cm2. On dash 7 and 8 there is pilot hose on top of each relief and the first stage is 355kg/cm2 while second stage is 380kg/cm2. These pressure settings are slightly bigger on dash 10 and 11.