old komatsu pc220-3

Bought at auction not running. After getting it home we got it running. It runs perfect, only problem is one track and bucket wont move and boom wont pressure down but will go up. other hydro functions work great. Bucket moved slightly while pulling one track lever. Pilot controls. don't think solenoid works or is getting power at pump toward driver side of machine. Looked at service manual but this system is way over my head. we pulled a couple spools of the circuits and they were smooth, swapped what we thought were relief valves but not sure (on bottom of valves). seems like a spool or relief is dumping oil to tank. I've owned and been around equipment over twenty years and have decent understanding for most repairs but my knowledge only goes so far... any help is greatly appreciated.

There could be a number of problems that can cause these issues. It sounds like either 1 pump is not stroking, or the oil is being diverted through an open relief. I think its unlikely to be a pilot pressure issue since you have functions that work. There is a few guys on here that are really sharp on the Komatsu equipment and could help you, but they would need the serial number of your machine. I would suggest first off, remove and clean any electrical connections at your main hydraulic pumps.......make sure they are not corroded/dirty. Check ALL your fuses in your fuse panels and replace what may look corroded. Inspect what wiring you can see, make sure the harness isn't chaffed/cut where wiring can ground out. It also sounds like your boom issue and your track/bucket issue are probably not related.

It sounds like on pump is bad. Boom down, bucket and one track all work on the same pump. When you travel and operate the bucket the straight travel spool shifts and combines both pumps on all functions. That's why things move a little bit when doing that. The solenoid installed on the pump controls the pump output when the engine starts to loose RPM. Generally if it doesn't work the engine RPMs will be dragged way down by the hydraulics.

You need to start at the easy stuff. Fluids, fuel filters, fuel strainer, air cleaner and hydraulic pump suction strainer. When you pull the hydraulic pump suction strainer look for brass particles. If any brass you looking at some very expensive repairs. Next will be putting gauges on the on the pump outputs and checking pressures.

I have a video on YouTube showing maintenance on Dash 5 excavators. The Dash 3 is very close in design so you should be able to pick up all the basics.


Good Luck

Sounds like you bought a good one. Lol

John C. said:

It sounds like on pump is bad. Boom down, bucket and one track all work on the same pump. When you travel and operate the bucket the straight travel spool shifts and combines both pumps on all functions. That's why things move a little bit when doing that. The solenoid installed on the pump controls the pump output when the engine starts to loose RPM. Generally if it doesn't work the engine RPMs will be dragged way down by the hydraulics.

You need to start at the easy stuff. Fluids, fuel filters, fuel strainer, air cleaner and hydraulic pump suction strainer. When you pull the hydraulic pump suction strainer look for brass particles. If any brass you looking at some very expensive repairs. Next will be putting gauges on the on the pump outputs and checking pressures.

I have a video on YouTube showing maintenance on Dash 5 excavators. The Dash 3 is very close in design so you should be able to pick up all the basics.

Good Luck

Click to expand...

I knew there would be someone here that knew more than I did on this machine. I had no idea that the boom up and down worked off 2 different pumps.

swapped pump lines and almost reverse issues. Id say no pressure from one pump ( one with tvc valve attached). trying to see if its in the control bolted to pump or the pump itself. We cracked line from pump not working, very little pressure coming out, like not even 50 psi. We didn't really see brass in oil. checked easy stuff nothing noticeable. Piston that moves swash plate seems like the little lever (pilot controlled) would never move it by trying to move it by hand.

The piston moves the swash plate. The little arm is just a linkage the is part of the controls that handle oil to the swash plate servo piston. Did you pull the strainer out of the hydraulic tank?

we disassembled tvc valve from pump. piston seems hard to move for that small of a lever running at pilot pressure. (Maybe its easier when running to move). strainer was missing (not good) but didn't see brass when we drained tank.

There are a bunch of springs behind smaller pistons in the valves that move that lever. It is basically a signaling linkage that provides a balance point that those control valves react to. You are correct about the strainer in the tank, if it is missing it is not good.

no brass in the oil so i find it hard to believe one side of pump is shot and other side is strong. Going to look into pump control, make sure both small spools that control control level to piston to swash plate are free to move. I watched a load sensing hydraulic vid on youtube that helped explain things. Possibly a chance it's de-rating the pump to nothing because stuck spool telling pump its not needed?

The whole control valve sections for each pump will come off in one piece. You can separate each control section one at a time and then pull the pistons and seals out. Be sure to note the direction the pistons are in when you take them out of the bores. They can go in either way but will only work correctly one way. Don't take the locking nuts loose on the adjusting screws. Just leave the adjustments alone and when you put them back in they should be close. The pump will need to be readjusted when you are done and I have a thread somewhere else on this site that describes how to adjust the pumps and main control valve.

Good Luck

good advice, thanks, I'll post as it is coming along, thanks

took off valving that controls pump output. on the control lever, spool that lever pivots on moves. spool behind that one didn't move. we took it apart and outer shell of spool and i think mirco spool inside wasn't moving. cleaned and put back together. machine still doesn't have output on that side of pump. going to test with gauges and see if small line have pressure.
curious, If the electric solenoid isn't working what will machine do? Default mode?

The TVC solenoid controls both pumps. When it doesn't work the pumps go to full stroke. There are mini screens on the inside of those pumps that can plug up and prevent signal oil from going to where it needs to be. You have to tear down the pumps in order to find and replace them.

Psi on pilot line going to swash control on working pump side is 300 psi. psi on pilot line going to swash control on non working side is 50 psi. tested at 90 degree turns at both valves near pump with small plugs. any ideas what's upstream with the little pilot lines that go to pump? I think some go to bottom of hydraulic of hydraulic valves behind cab. I'm not quite sure how that part works, but I do know somewhere there is pilot psi missing. we swapped what we thought was relief valves on the bottom of the pilot operated valves and nothing changed.

If you check the side opposite of the TVC valve solenoid you will see what look like two bolts with caps on the ends of them. That is where you check the pilot pressure for each pump. That is the oil going to the end of the servo piston for stroke control.

There will be two hoses on each pump that come from the bottom of the main control valve. Those are jet sensor hoses. The control valves are open center with parallel passages. When nothing is being used oil from the pumps go down the center of the valve and hit a dead head at the bottom. There is an orifice at that point where a stream of oil will enter one of those hoses and go back to the pump where it will put pressure on one side of a control spool. There is a relief valve in the same cavity as the orifice in the main control valve that maintains a pressure when nothing is being used.

Now lets use something by stroking one of the valve spools. Oil is routed away from the center section of the valve to the implement. When that is done flow in the center of the valve drops which reduces the flow through that orifice. Now oil that has gone out to one side of a cylinder needs to have oil come back to the main valve and is then routed to the cooler and then the tank. The drain cavity in the main control valve is connected to that other small hose that goes back to the pump and pushes against the opposite side of the control spool that the jet sensor is connected to. As that return oil flow comes up it increases pressure on the drain cavity hose. So as jet sensor pressure drops and drain pressure increases the control spool in the pump is moved as the difference in pressure gets closer to the same. That is the basis of an open center load sensing system. The book will refer to this pressure as negative control, or NC pressure, but usually negative controls for other manufacturers only turn the pump on and off and you will only find one hose from the valve to the pump controls.

You might remove the jet sensor relief valve and check to make sure the cone inside isn't worn. The valve cartridge can be taken apart. Like wise you should remove the jet sensor and make sure the orifice is not obstructed. They are both cartridge type fittings on the bottom of the valve.

At some point in the future I plan on doing some video of the adjustment procedure for these systems but right now I have other projects to finish first. Let me know what you find and I might be able to walk you through it. I have described it before on here and you might be able to find it by searching on Komatsu and troubleshooting.

will do and thanks so much for helping!!!! very appreciate it

okay, we have swapped two sets of relief valves from one column of valves to another, taken two others apart and cleaned-no difference. We took the three small housings with small spools and internals that control pump apart, cleaned and no difference. My friend swapped pump pressure and two pilot size lines on pumps and functions that didn't work-worked and functions that did work-didn't.

front pump 195psi at idle
900psi at WOT
4600 at WOT actuating controls

rear 10 psi at idle
45psi at WOT
doesn't change with actuating controls

Im assume rear pump is bad. I feel like we have been through the whole small loop finding nothing but pump won't put out pressure but does move volume

Ive spent two weeks trying to find any kind of parts or info on this machine and finally i found this thread which isnt exactly the same issue i have but contains a lot of helpful info I can use to work on mine and somewhat points me in a direction so thank you fellas