About 2 yrs ago my swing started hanging up. It got progressively worse and when it did release it would sometimes cause a bang once released. It eventually would no longer swing. Not having a lot of experience with working on hydraulics I reviewed my parts manual and decide to replace the hyd. electric switch for the swing (P/N 141-0597). This fixed the problem however a year or so later the same gradual progression of the swing issue happened again until it would no longer swing. I replaced the same switch but this time it did not fix the problem. You can see the hyd lines become pressurized when activating the swing in each direction but nothing happens. I did disconnect this new switch and by passed the switch by using a small wire loop and the swing would work. No ability to stop the swing but it did swing. I then had the Hyd. pressure checked where this switch threads in and the reading was approx.. 400psi. I am not sure what it is supposed to be as I do not have a service manual. Also I did change the pilot servo filter just in case this may be plugged or dirty but it did not help. Does anyone know what the pressure should be at to activate that switch? Any other diagnoses advice/next steps? I placed an image of the switch that I replaced. I disconnected the (green) plastic electric connector and jumped this and the swing motor works as mentioned above. I also placed an image of the swing motor if needed.
From your description I think your new switch is bad. It should just be looking for pilot pressure for swing to send power to unlock solenoid. 400 should be fine for pilot slim chance pilot pressure is to low to close switch but I highly doubt that.
I think the small line would be your brake release
I second that small line should be brake. It should go to a solenoid on pilot manifold. And I would think that switch operates the solenoid based on the oil pressure it sees. When u had pressure tested did it have 400 all the time or only when swing was commanded ?
Swing parking brake function is usually controlled by a timer in a computer. Basically, pressure switches are installed on the pilot control circuits in the hydraulic system and are normally open. When you operate a function the switch is closed which tells the computer that you are doing something and the swing brake needs to be released. The computer then grounds the swing parking brake solenoid which opens a valve that send hydraulic oil to the swing brake release piston. You can test the switch with an ohm meter. You can test the solenoid coil with an ohm meter as well. The switch will be open when doing nothing and closed when you operate the swing. There should be around five to fifteen ohms of resistance through the solenoid coil and no continuity to ground. I haven't done much with B series machines but I think you can read this stuff in the monitor panel if you know the correct menu codes to go into. Below is the description of how to get into the code menu and what the number items are. I don't have a video yet that shows how to do this.
Attached here is the list of codes for the B series Cat excavators.
I thought the same thing that the switch may be bad so I purchased another one and it did not change the issue. I should have included this in my original post.
When. Pressure was taken where u getting that 400 psi all the time or only when swing was activated?
Thanks Jon C for all the info. As you can tell I'm a newbie at this but do I need some computer / scanner to check the codes? Also of note I put maybe a total of 50hrs average a yr on this machine so it does not get much usage. Added info on Machine: Machine ID 7NF02956 (1990) Arrangement # 9X0539 I will check the ohms on the switch but not clear on how to check this? Do I verify ohms while the hydraulic fitting is threaded in place and I activate the swing? Or can I check this disconnected. What should the Ohm reading be at the switch? Also not clear on testing the Ohms on the solenoid coil? Is this solenoid coil located in the side compartment where the servo Pilot lines run into? I attached an image of this below. To answer rmllarue91 I had 400psi only when activating the swing. Also, yes the small line shown in the previous image is the swing brake release and it runs to a solenoid on pilot manifold. Image below shows the electrical connection for the swing that leads to this solenoid on the pilot manifold. Thanks to all for the info!!
You can check the switch as you said. Disconnect the switch at the harness and connect you leads from the ohm meter to the switch side. Start the machine and operate the swing while watching the ohm meter. It should have infinite resistance when the machine is off and no resistance when the swing is operated. To check the solenoid coil just disconnect the harness plug and touch the pins with the ohm meter. You don't need to have the engine running to do this.
So I had some time today and checked the Ohms on the switch and the solenoid. As you stated I did obtain approx. 15 ohms of resistance on the Solenoid. The Switch however did not change state when the swing was activated. This happened on all 3 switches I have. 2 are brand new so I can't imagine all 3 switch's are bad. Do you know what the pressure is to activate this switch? Perhaps the 400psi is not enough? Not sure what to do next?
Are these oem switches ? I dont have info on this machine to help you more.
I would wonder if pilot pressure was getting to the switches at all. Take a switch out and plumb in a gauge. Then try it.
I tried to find details regarding the 141-0597 Pressure Switch and came up empty. Apparently it is a part dating back to the days of the Cat/Mitsubishi alliance and Cat don't carry the specs for it. The only thing I can suggest is to plumb the switch into a porta-power equipped with a reliable gauge and slowly pressurize the switch while monitoring the resistance. It would at least give some idea of what pressure is required to close the contacts.
Have you verified in the monitor that the solenoid is getting signal when you try to swing? The ECM will make it wait about 3-5 seconds to set the brake once you release the swing lever. I’m beginning to wonder if there’s a wiring issue and solenoid isn’t getting its signal all the time. You can rig up a temporary setup to energize the solenoid independent of the ecm control and machine harness. I’ve had to do that on some drills when we’ve had issues. Might be worth a try considering you’ve got a couple extras to try with.
Yes these are OEM switches
I have done this already and the reading was 400psi.
That's a great idea but I will have to try and find someone with a porta-power unit.
How do I verify the solenoid is getting signal? This is an older machine and it has no monitor? As mentioned in my original thread when I unplug the switch and jump the solenoid the swing works properly but of course there is no brake when the solenoid is jumped.
You can use the mili-amp setting on your multimeter in series with one of the wires in the harness connector to see if the signal is coming from a processor.
So I had someone check the switches with a porta power unit. The original switch that I put in the machine the 1st time this acted up took 425psi to activate and the brand new switch I have took 475 psi. to activate the switch. I then checked the hyd pressure again on the machine after removing the switch and that was 375psi. So that explains why the switches were not working. I turned the pilot relief valve up about 3/4 of a turn and that fixed the problem. The machine swings as it should! Based on this do you think the pilot pump is starting to loose power? Anything else I should verify or just run the machine. Thanks again for all the great advice!!
It's more likely the spring in the regulator valve cartridge got a little weak and drifted down a tad. Turn it in to spec and it should be fine.
Thank again John for all your assistance!! Happy Holidays to you!
Glad that idea of testing the switch off the machine worked in guiding you to the real problem.
Wish me luck... just got a machine with this same issue! Off to troubleshoot....
Hi sara, Did you able to solve the problem using these same steps ?