It took us a little over a year to resurrect our "beast" which required replacing bearings in the hydraulic pump, replacement of the pilot pump, replacement of both drive motors, and myriad lesser issues, but now have a machine that runs good and working. Since the computer was missing when we got it and found that it had been crudely wired to run in backup/bypass mode we went ahead and made a new control panel that has a dedicated toggle switch for each each of the ten solenoids including the proportion valve on the side of the pump. Though armed with manuals and advice from members of this forum and a local service manager there are still a few questions that remain to be answered. In order to get free swing we energize the solenoid labeled Swing Short on the wiring diagram which releases the swing brake. But when travelling or working side hill we have to turn that switch off to keep from swinging. The wiring diagram shows a switch labeled Press SW (Swing control line) which I'm guessing is what disconnects the Swing Short solenoid (swing brake when off). Where is that switch? There is another solenoid labeled Cushion. What is it's function? The Proportion valve is fed 24 volts through a 25 ohm resistor per the Backup switch wiring. Does this valve control pressure on one or both pump sections? I was told that it is controlled by "millivolts" which makes no sense since it is controlled by current through the fixed 25 ohm resistor. I guess I'm just not getting a clear understanding of it yet. Any help is always much appreciated! Thanks, -Tom
I think most of my memory of those machines is gone, but I'll see what I can pull up. Maybe I can clear up a couple of thinks. Free swing made the machine act like a friction machine. The house would just keep turning when you left off the handle. As I recall it was mainly for logging machines and not necessarily excavators. I believe in the case of your swing brake, it is only a swing parking brake. Power to the solenoid just releases the brake. The swing will drift is the swing brake is released. The proportional solenoid does have a constant voltage. It is controlled on the ground side of the circuit by the computer and is measured in milliamps. As I recall the more amperage going through it equates to more output of the pump. I can be wrong about that one very easily. It does control pilot leak off of both pumps. It is kind of the fail safe to keep the pump from pulling more torque than the engine can provide. The cushion function just changed how the pilot controls reacted to the operators handling of them. Basically is softened how hard the pilot pressure hit the main control spools and made the machine a little less jumpy to the operator. I could be wrong about that one also. Good Luck!