1980 komatsu pc 120-3 excavator slow swing an bucket

[fish boat billy]

previous owner stripped all wires on machine boom works up an down but swing an bucket crawl unless I'm working boom up and down then they seem to operate with in reason yesterday swing stalled completely I pulled a solenoid valve off the main hydraulic pump and put power to it to see if was working it was so why did previous owner cut the wires to it ? while it was off tried moving piston that plunger hits from solenoid don't think it moved but I did hear burping in hyd tank put it back together an swing was working seems like fluid is building back pressure until I work boom any ideas would be great thanks

 

[John C.]

Does the travel work right when moving the machine and operating one of the other functions. There is a setup in there for straight travel. It works by combining pumps when you operate something in addition to traveling the machine. There are micro switches on the linkages under the floor of the cab on the travel pedals. What happens is one or both get stuck and cause the switches to stick on. It shifts the straight travel spool in the valve closest to the hydraulic tank and dead heads one pump.

Does this machine have manual controls or pilots?

 

[fish boat billy]

seems to drag right track some an it has manual controls all the wires visable have been disconnected

 

[John C.]

By manual controls I mean do rods and pins go from the cab to the control valves? There is a mode knob in the cab. Does it have two settings or three? It will be S and L or H, S and L.

 

[fish boat billy]

I will check switches Monday id be totally surprised if wires aren't already cut on those to. Any idea Where a good place to start trying to find shop manual for this machine is I haven't had much luck so far

 

[fish boat billy]

By manual controls I mean do rods and pins go from the cab to the control valves? There is a mode knob in the cab. Does it have two settings or three? It will be S and L or H, S and L.

yes rods go to linkage behind cab that go directly to valves

 

[fish boat billy]

I didn't know about the switches but I will check tommorrow

 

[fish boat billy]

Thanks for reply john machine has S an L switch in cab an checked under cab today no switches did find 2 in linkages just in front valve manifold an all wires disconnected one large solenoid on the pump thats disconnected im wondering if this was hook up to travel switches ?

 

[John C.]

The solenoid on the pump controls the modes. You have an early machine with just two modes. There is no computer, just a resister that varies how far a piston on the that solenoid goes in and out. The straight travel valve as I recall was manually controlled in that case and there are no switches under the cab floor on the travel pedals.

So then you need to check all the linkage connection points. There are what are called throttle ball joints on the ends of each reach rod. The ball ends wear out and get broken over time and cause lots of issues. There is a big linkage stack behind the cab where everything turns ninety degrees to go to the valve spools. That stack has to be stationary when you move the control sticks. I've seen that mess come loose and cause the same kinds of problems.

Good Luck

 

[fish boat billy]

Thanks

 

[Dannyboy63]

Any updates?.....I got a similar issue..