Hitachi EX120-2 swing issues

[dirwood]

Still having trouble with the swing brake applying while slewing machine, checked the wiring to the brake solenoid (or at least what appears to be) and it looks good. Based what i have read on other forums this can be caused by a bad swing pressure sensor? Does any one know where the sensor is located, and what the swing brake logic is? Pressure should release the brake and it should set via spring pressure when pressure is removed, does the solenoid at the base of the boom control the brake pressure?

Thanks for any suggestions or information you may have

 

[uffex]

Good day dirwood
This explanation from Hitachi information may help:-
Swing Mechanism
Axial piston motor with planetary reduction gear is bathed in oil .Swing circle is a single-row, shear type ball bearing with induction hardened internal gear. Internal gear and pinion gear are immersed in lubricant.
Swing parking brake is spring set/ hydraulic -release disc type.
Swing dampener valve in the swing circuit prevents coasting when stopping
swing. Swing cushion valve built in the swing motor absorbs shocks when stopping swing.
Swing speed 11 revolutions per minute.
This suggests as most hydraulic excavators the stopping go the swing motion is achieved by the swing motor changing its function to a pump, the brake is in effect only a negative parking brake which applies when the swing motion is static.
Testing the machine according to normal practice can be found at

Kind regards
Uffex

 

[dirwood]

This machine continues to have problems with swing brake setting while rotating and appears to be getting more frequent. I installed a gauge into the brake line and observed the pilot pressure to brake to be dropping to zero causing swing brake to apply. A couple other things i noted are that the pilot pressure to the brake is around 800psi, this seems a bit high. Another thing that may or may not be note worthy is the brake release pressure stays on for about 4-5seconds after controls are returned to center. When swing is stopped by the drop of pressure to the brake and stick is returned to center it seems to take about 25% stick input to get the unit swinging again, you can hear the hydraulics load up but brake isn't releasing immediately. Operator noted that the problems seem to be worse when heavy load is on the machine such as handling a cement hopper. I am not sure exactly how these controls are set up but one thought i had was that perhaps there is a solenoid valve that is heating up and dropping out which in turn drops the pilot pressure to the brake, additionally that perhaps the high pilot pressure may also be a contributing factor.

Look forward to any thoughts or suggestions folks may have regarding this issue,

JW

 

[uffex]

Good day JW
The delay before the brake applies would be common practice with excavators it prevents the brake activating before the swing motion has ended, if this delay was not the case it could cause transmission failure. The brake release occurs by pilot pressure in both directions, arm in is often included releasing the brake and allowing some movement when cleaning the trench sides for example. The pilot pressure of 800 psi is high suggest you check the pilot pressure both with low and high revolutions.
A point worth taking note is that the brake operates only as a parking brake it has nothing to do with stopping the swing motion this is provision is by the motor turning to a pump function forcing the exhaust fluid by relief valves. There are two of these normally mounted in the motor head, one for each direction. The fact that the swing brake requires more than normal stroke may well be an issue with pilot pressure.
Kind regards
Uffex

 

[Knivens894]

Hello Dirwood;

There are two pilot pressure valves on the right side of the pilot valve manifold. As I recall, the top one has shims which controls the gross pressure to the manifold. The lower one regulates the pressure delivered to the various PRESSURE REGULATING CONTROL valves for each system and is factory set and can only be fixed by replacement (about $500). Each of the pilot systems pressure control valves can be removed, cleaned and overhauled with new O rings. Be careful to go by the manual if you undertake this task. Orientation of the inner sleeves to align with the ports is critical. I would first put a pressure gauge on the swing brake pilot system to see what you are experiencing during the swing interruption. There is a test procedure in the manual for each system. I have attached a diagram of your system. I have tried to attached the operation and test manual which gives all the adjustment criteria, but the file is too large. Send me a direct e-mail at Knivens894@aol.com and I will send it to you.

It would seem the sudden application of the swing brake would be more of an electrical problem to that solenoid valve coil. The coil itself can be tested in place to check its resistance as given in the manual.

The signal to the coil or a defective coil could cause the problem you are having, or it could be a defective solenoid pressure regulating valve for that system. The computer sends a signal to release the swing brake when "boom in" or "swing" is input on the controls. I would also check the condition of the wires and connector on the swing brake control solenoid. Releasing the swing brake requires pressure from the swing brake pilot control solenoid. If you have that constant pilot pressure during operation, the swing brake should be released. If you check that pilot pressure first and it is within specification for that system, the other problem might be a faulty main relief valve or main control valve for the swing brake system. In other words, if the pilot system is reliably telling the main swing brake control valve to open and it is not remaining open, then the main pump pressure to the swing release valve might be bypassing the system through a defective relief valve or control valve for that system. That defect may be a simple as a defective O ring on that system's main control or relief valve, allowing the pressure to bypass. I know JD wants at least $500 for every one of their valves, so locate the problem first or you can spend a lot of money quickly.

Hope this helps!! Good Luck!! These machines can be a PITA to find the cause of problems.

Kirk

PS: After writing the above I read your previous posts. If the pilot pressure is there without interruption, move on to the main control valve and relief valve for the swing system.

 

[dirwood]

definitely am losing pilot pressure to the brake and it is setting while rotating, have installed gauge and verified pressure drops. Does anyone have the spec's for the coil resistance? Also thinking about sticking a multimeter on the wires to the coil to see if the voltage is dropping at the same time pilot pressure is dropping. What should i see at the coil, 24volts? Not sure what the controller is outputting for signal to coil. I did remove the plug from the coil and the connections looks great, even tried pulling, tugging, & wiggling the wire and connector while operator rotated machine to see if there was a flaky connection in the plug.

As for checking pilot pressure at various rpm, we are getting 800 psi at economy and power settings, when back at idle the pilot pressure is around 610 and pulses a bit while swinging, dipping to 590psi.

Thanks for all the information, will be back on it Monday

 

[Knivens894]

Check the coil on the pilot solenoid on the coil for the swing system first thing. Resistance specs are in the manual I sent to you. If not to specs, replace it. The pilot pressures seem reasonable. Have you checked the pilot control regulating valve pressure on the right bottom of the pilot control block? Again specs are in the manual. If out of spec, the only repair is replacement. I would suspect it is OK because you are not having problems with the other systems.

 

[dirwood]

After some more digging and a lot of reading of the service manual that Knivens894 so kindly emailed me i was able to determine the problem was a faulty swing pressure switch.

 

[Lee serman]

Any way you could email me that manual I'm having a time with my 120-2 my email is lsermanexcavating@yahoo.com

 

[Timberking]

Dirwood.... Where is the Swing pressure switch?... I know where the selinoid is but have not found the swing pilot pressure switch.. think mine is bad