Okay, I can't seem to figure out how to put pics in and keep writing. Anyway. I had a client buy a broken machine. I get pretty annoyed when they do that. Especially in this case. Because it used to belong to another client and I knew I didn't want to try to figure it out. Actually told him not to buy it. I don't know if I should be upset that he didn't listen or flattered that he is so sure I can fix it. Complaining aside, here is what is going on. Machine lost all hydraulic functions. The Komatsu dealership worked on it for about a month. I am missing some info here... I know there was something about losing a spring in the main valve body during the process. I see one new component. (here comes another pic)
Pretty close to center. The shiny piece. Now the machine can track. And the dealership gave up. My client cracked lines to lift up the blade, took off the bucket and loaded it up and dumped it in my lap. I have been glancing at it annoyedly for about ten days now. I started to look at it today. Some weird stuff happening here. The only function that actually works is travel. You can hear the engine load up if you operate the swing function. It of course does not swing. Both of these things happen regardless of the pilot lock out lever being engaged or not. Pilot switch works, pilot relay works pilot solenoid coil engages, (if I am correct in my assumption that it is the leftmost coil in the next pic).
Oh, yeah, the travel alarm is softly on all the time.
I honestly have no idea what the other four solenoids do.
I have a manual for a PC78UU-6 machine and I don't know how different they might be but if you want a copy send me a PM.
I would like that. I can't seem to find out how to send a private message.
Just trying to bump this thread up. Thanks to John C. I have a little service info (My hero!). The pilot lock problem was a stuck solenoid spool. Didn't solve anything else. When I did not want to work on this machine 6 years ago, the dealership replaced the entire hydraulic pump assembly as well as the control valve assembly. Somewhere in there the original client asked me to look at it again and I said no. If the dealership threw 15 or 30 grand worth of parts at it, billed you and it still doesn't work... Doesn't that make it their problem? Apparently, in the end, the dealership had it working. But now we are back to an eerily similar situation. And I would personally rather set the machine on fire and casually stroll away like Keyser Söze than throw more parts at it.
Made some progress today. Finished running through the pilot system and found good pressure all the way to the control valve. Pulled the end cap off of the bucket control valve and found the spool stuck. Took quite a bit of effort to get it to spool free. But then the bucket cylinder started to work. Same thing on every spool in the control valve except for the swing valve, which started to work on its own about halfway through the day. All functions are pretty weak, it seems like the only function that is stroking the pump is travel, so I have to load up the travel circuit to move almost everything else except the blade. I think I understand that, thanks to the service info that John C. provided (once again, thanks) the pump is actually three pumps (four if you count the separate circuits on the main pump) main pump, gear pump and pilot pump. The blade runs off the gear pump (so does one other function but I am totally blanking on which) I haven't found any metal debris. The spools just seem to have been glued in. they had a film that for lack of a better term, I am going to call varnish. I suspect this is a result of mixing zinc less oil with standard hydraulic oil. So, for anyone following this thread, my current symptoms are as follows: (With my current theory in parentheses) 1. Most functions do not stroke the pump. (Something stuck in the load sensing circuit) 2. Boom will not lower. (Something stuck in the boom lock section of the control valve) 3. No swing brake and no two speed travel. (Stuck solenoids in number 2 and 3 from the picture above) 4. The engine will stall with travel held against relief as well as the offset cylinder against relief. (Something stuck... That's all I have) 5. Still pretty annoyed at the client for doing this to me, and really disappointed with the dealership. Six years ago they replaced a hell of a lot to solve a problem and failed to deal with the root cause. Two months ago they replaced the main hydraulic relief and somehow did that without disturbing the paint on the test ports for testing hydraulic pressure.
So,my questions now are: How do I clean out this hydraulic system? Why isn't anyone actually interested in this thread? Because this is the most diagnostically interesting problem that I have been up against in years.
Finally have gotten back to this machine. Been pretty swamped with undercarriage work on a couple of dozers and excavators. And it is a holiday week so I have a little breathing room. Did a pretty thorough hydraulic cleanse of the entire machine. Actually got more waste oil out of it then the book says it should have and it was low on oil in the tank to start with. No change in any of my issues. My working functions are blade, travel, swing and offset. Boom arm and bucket functions are almost nil. They only really move when you use travel or offset. My flow meter is telling me that at full idle and oil temp in the 120f* range I have 22 gpm at about 800 psi. Which has me looking at the load sense circuit. I know I am looking for about a 350 psi delta. But what I am reading at full throttle is 150 to 175 psi in the wrong direction with the controls in neutral. My low side pressure is higher than my high side pressure. It does not change when I curl the bucket. But then the problem is that curling the bucket does not "stroke" the pump. If I try to hold offset against relief both gauges quickly climb to 3000 psi and then stalls the engine so I really can't get a good reading on the delta. If I try running one track forward just enough to make the bucket curl without actually moving the machine, I read a pretty constant 1200 and 2000 psi . Still 800 psi in the wrong direction. Here the flow meter shows 18+ gpm at 2000 psi. I know that this isn't the way the test is supposed to be done but I am trying to get my head around this problem. I am assuming (and there is every chance that I am wrong) that the only reason I can run any of the digging cylinders when I offset or travel is because the oil from the gear pump is being added to the circuit. But then why doesn't running the blade or swing have the same effect? While I am talking assumptions, I am not sure which pump offset uses. The configuration of the control valve makes me think it does. Any help is appreciated and to those of you in the states, happy Thanksgiving.
Bump
I am fairly new to this message board, so I am not really sure how it works. I know that no matter how many times I cruise new posts I never see anything that I have started. So I don't know if there is a default filter that takes out my posts or if nobody actually sees these. As an experiment, if anybody is actually reading this; please respond. Just a character or two. FU would be just fine. So (I sort of think that I am only entering data into my own journal of this problem) got back to this machine today. I pulled the logic valve and boom valve out of the main control valve. Tore everything down and freed up the sticky stuff. Apparently a good move. I now have good functionality on the boom, stick and bucket without tracking. Actually, pretty close to the cycle times the manual says I should. However, my pressures are a bit low. Boom up, stick out and bucket out only hit 1900 psi. Boom down, stick in and bucket in are around 1300.
I haven’t ignored you. I’m away on the road and haven’t been able to put enough thought into your problem to be able to give you the best answer. The Dash 6 line had lots of design problems and the zero turn machines ended up being an in between model that only had a partial computer system. Give me a day or two more to consider this.
KOMATSU PC78MR-6 and PC78UU-6 are almost the same. You can access the service menu to display the service code. Does this machine display any errors on the screen? for your reference https://www.mediafire.com/file/v3f3g3qnmkclk4u/PC78MR-6+SEBD030604+shop+manual.PDF/file
1/- Most functions do not stroke the pump==>I suggest you check, adjust (if necessary) the LS valve (see attached .pdf file). And/or remove then disassemble the main piston pump regulator completely to see if the inside is stuck? 2/- You're right. 3/- You can see the picture below to refer to the exact solenoid block. 4/- As (01) above, I suggest you remove then disassemble the regulator of main piston pump completely to see if the inside is stuck?
First off, John C, you have been great. My post last night was mostly about not understanding why no one seemed to be chiming in. I was wondering if I posted it in the wrong place. Lachau, thanks for replying. I was thinking of pulling the regulator. Sticky valves have been the culprit everywhere else. I will post more on this tonight. I am currently fighting with a 312 b that won't climb up a slope. And I know that if I post more here on the pc78 that I am going to start getting my symptoms confused between the two.
Hey sir, did you ever find the culprit? I also have a PC78 with a weird problem, lower power with all functions when cold, low power and easily stalls when warm (even after 5-10 minutes running the machine). I only have basic skills, but I've changed the filters and checked the levels on everything, I'm now going through the fuel like looking for blockages or debris, but haven't found any. Engine runs smooth and starts right back after stalling, never any smoke while running the machine or just prior to stalling.
Sorry, TexasDan. I didn't see your message. My stalling problem was caused by sticky spools in the pump control body. I doubt that is what is going on with yours. Stalling with no smoke would make me suspect the ppv solenoid. I have changed a few. But I don't think I ever found a bad one that didn't also throw an error code on the monitor. I think I would make sure the turbo spins free and doesn't have excessive play. You probably know this; but Komatsu likes to hide pencil filters in banjo fittings. Either in the banjo going to the water separator or the one on the inlet of the injector pump. I don't mind you hijacking my thread, but it is a pretty unpopular thread. You might get better advise if you started your own. Good luck and I would like to know what you find out.
JohnC and Lachau. Yes, sticky spools in control valve. I finally got back to this machine yesterday and felt like a rock star when I tore apart that valve, freed up the sticky parts and everything started working perfectly. Almost. Get to that in a second. I can't thank the two of you enough for your help. I only have one issue left. Due to the unpopularity of this thread, I am going to start a new one for that. I have swing overrun. Machine does not stop swinging or swings with gravity until the swing brake applies. I have gone through everything that I could think of on this and got so frustrated that I actually called a handful of local techs that I respect. I was kind of shocked to learn that they all believe that the swing brake is what stops the upper structure. The new thread will be called pc78mr swing overrun.
JohnC and Lachau. Yes, sticky spools in control valve. I finally got back to this machine yesterday and felt like a rock star when I tore apart that valve, freed up the sticky parts and everything started working perfectly. Almost. Get to that in a second. I can't thank the two of you enough for your help. I only have one issue left. Due to the unpopularity of this thread, I am going to start a new one for that. I have swing overrun. Machine does not stop swinging or swings with gravity until the swing brake applies. I have gone through everything that I could think of on this and got so frustrated that I actually called a handful of local techs that I respect. I was kind of shocked to learn that they all believe that the swing brake is what stops the upper structure. The new thread will be called pc78mr swing overrun.
I am happy that you have detailed the cause of the failure and that you have completed the repair of this machine. We will continue to discuss swing overrun symptom.
Glad you got the first part figured out. Looking forward to hear about fixing the swing function.
Well I can't explain this. They moved the machine to the other side of the yard last night to clean it up a little and now the swing is working. I am going to put it back together and let them run it. Thanks again.
Hello I am new here and I have pc 78 mr 6 And can someone send picture of valve who needs to clean because every function is not good