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.