I have a 2008 CAT 272C RED01375 that has been rebuilt from an engine fire. All prior issues with it have been fixed; only this one persistent problem is left. I have never used the machine and was not the owner when it caught fire. The machine is sitting on blocks and the chains from the motors to the wheels have been disconnected. The machine shows 40 hours, which is not accurate. I suspect that the ECM was changed before I bought it. An expert from CAT estimates the machine has 2k hours based on the wear of the gear pump. The issue is that the left side motor will only spin in reverse, even when directing it forward. The right side does not have this issue, and this is confirmed not an issue with the motors, as they have been swapped and the issue remains on the left side. I have a simple on-board diagnostic monitor that shows the ECM is reading the x and y-axis of the yoke correctly. The motor is also slow to come to a stop when the yoke has been released; it completes another revolution or two before it ceases movement. The Hydrostatic pump has been pulled, cleaned, and all the seals replaced. It was pulled a second time, maybe a month or two later, when the swashplate bearings were replaced in an effort to fix this issue. There were no visible issues with the pump either time. The charge(gear) pump was also cleaned and had the seals replaced. The gear pump does have some wear, but I brought it to my local CAT dealership and showed one of their experts; he concluded that it would be unlikely to cause this issue(and gave me the estimate of how many hours the machine has). The control units that sit on top of the hydrostatic pumps have been swapped, and nothing has changed. Swapping the 4 cross-over relief valves changed nothing (I swapped 2 at a time, the left to the right). I disconnected both of the solenoids on the control unit for the left side pump and attached dummy solenoids to the wiring harness so that I could operate the machine. The left motor still spins in reverse when I move the yoke, again, regardless of what direction. Disconnecting the right side solenoids results in the expected outcome of having no movement. This makes me think this is a mechanical issue, not an electrical one. Neither motors move until the yoke is moved, meaning the swashplate is not stuck, or I imagine that would result in immediate movement as soon as the parking brake is disengaged, or worse, cause issues starting the engine as it would try to spin the motor while the parking brake is engaged. I do get codes on the on-board diagnostics: e570-2 and e571-2, but they are not current and I've bought 3 different speed sensors, at first just one for the left side as that was the obvious culprit, but when that didn't fix the issue (and swapping left and right sensors didn't help) I bought another 2 to change both at the same time, also to no avail. I do not have access to CAT ET and probably won't. I am completely stumped and have no idea where else to look.
If you went into diagnostics while the machine is running and tried to move the drive motors I bet those Events would become Active. At least they show the speed sensor outputs are good, alhtough because they both refer to the RH motor the possibility exists that the speed sensors are cross-connected. E570-2 - Unexpected Right Motor Forward Speed Detected E571-2 - Unexpected Right Motor Reverse Speed Detected These events indicate that unexpected motor speed in the indicated direction has been detected. The direction of the wheels/tracks has moved faster or slower than expected. Ensure that the latest available machine flash file is installed. Probable Causes · Pump stuck at maximum displacement - Motor speed will stick in max turtle gear ratio · Motor stuck at minimum displacement - Speed will be stuck in rabbit gear ratio (two-speed machines only) · Intermittent diagnostic for a motor speed sensor · Active diagnostic code for the hydraulic temperature sensor Refer to attached Troubleshooting, "Motor Speed is Unexpected". Check your message inbox for an electrical schematic.
Yes, I've seen this before and I have the schematics for the machine, I'll see what I can do to make some codes show up tomorrow, but when I'm running the machine it does not show codes until it locks out into park, it's been more difficult to do since buying the new speed sensors, swapping the motors and putting in the new bearing for the swashplate. it used to regularly park and show codes after a few seconds, but now I have to get to 2k rpm and fiddle with the controls and creeper mode to try to get the left motor to go forward, which it does only for a second, it then either continues to spin in reverse or locks out into park. Frankly, my main concern is how the motor is getting oil with the solenoids on the control unit being disconnected.
Swash plate servo is suspect. The motor is just a receiver of oil. It doesn't shift directions internally. Supply lines, let's call them A & B. To go forward, A pressurizes and B goes to tank. To go in reverse, B pressurizes and A goes to tank. A & B receive pressure from the pump. At standstill, the swash plate is centered, resulting in no oil to A or B. To go forward, the swashplate tilts to the positive side, pressurizing the A line. To go in reverse, the swash plate tilts to the negative, pressurizing the B line.
It doesn't have a servo, the hydrostatic pumps each have a control unit with two solenoids that move a small "spool" (I don't know the exact name for it) that will pass pilot oil to a piston that moves the swashplate. I've ruled the control unit out by swapping the left and right pump control units with no change. I have also completely disconnected the two solenoids with no change. Somewhere, somehow, "line B" is getting all the pressure. I don't know if it's a secret valve somewhere that is stuck and is passing everything from line A to B or the swashplate is somehow turning on its own. And from my understanding the supply lines to the motors are bidirectional, and will flip from pressure to suction depending on swashplate angle, with a 3rd hose being a case pressure drain (and a 4th parking brake).
Since you have tested the duty cycle output of the joystick position sensors it would appear that the only remaining test before condemning the hystat pump is to check the input to the four pump control solenoids. I would suggest to either backprobe or use a set of piercing probes and measure the voltage across the each of the four solenoids while monitoring the duty cycle % of the relevant position sensor. If the LH & RH side FWD & REV inputs are identical, or at least broadly similar, then the solution is to replace the hystat pump because at that point you will have eliminated every other possibility.
That "spool" is part of the servo control.
Being that it was in a fire and I’m sure some, if not all lines got burned up, is there any chance something is not hooked up properly. Have you tried swapping drive motors?
It says so in his first post. To the OP. I don't know if you have seen this document before. It may be of some use.
Yes, we swapped the motors, we swapped the controllers from left to Right, and right is working right, but left is still causing the issue. We disconnected the solenoids on the Left side of the pump, and it is still nothing changed. It seems to me that some pressure is still coming to the Servo controller piston, moving the swash plate to the negative side to move the motor backward without control solenoids being connected, but I cannot figure out where this pressure is coming from. I am assuming the servo piston is the whole thing 27 with springs and two-sided pistons. It has two caps from each site, and you adjust this unit with the swash plate in the centered /neutral position. It stays in neutral, but when I move the joystick forward, it goes backward, and yes, we swapped hoses, and it goes forward, but forward only. Also, it did not have fire in the area of the pumps at all, and all the hoses were connected originally, and they were intact. So, we tried everything, and now we are stuck because it looks like whatever we spent money on a new idea, it does not work, and all stays the same. It does not feel it is electrical because we disconnected the solenoids from the controller on the left side of the pump, and as always, nothing changed. We thought about the brake-solenoid on the side of the state and the relief valve, because these things we have not changed yet. LOL. This is the side cap for the servo. It has two, one on each side, to center the swash plate. Number 11 relief valve and 12 brake solenoid. These two things are left to change. If anybody has any idea what we can do, please share.
As I already mentioned personally I don't think I would be prepared to rule out something in the electronics until the input voltage to the four solenoids had been checked versus the output duty cycle of the appropriate joystick position sesnor.
Could be a bad joystick?
When you say you had the hydrostatic pump checked I assume you know there are 2 pumps together end to end? I had one of these pumps that had a bearing between the 2 pumps migrate up from its bore and lift the swash plate slightly of its seat in the pump housing. It made the direction control hesitate. I wonder if it was bad enough if it would mess with swash plate hole timing with oil crossing over behind the plate.
It doesn't look like that's the case for this one, I can't see how the sleeve bearing could even move the swashplate, it would be pressed up against the distribution plate, but even if it could, it doesn't look like the bearings are out of place when I take it apart. I'll probably be taking the pump out again soon, but for now I'm re-examining the control unit. I've noticed that the spool is not symmetrical and one side has more lands than the other, this may be significant if I flipped it when reassembling, but I'm not holding my breath considering I've swapped the units between pumps. The only way I can see this being the issue is if the left pump requires the lands to be on one side and the right pump on the other and when I reassembled I put them both on the same side, so regardless of if I switch them it would be on the wrong side. This theory is ultimately defeated by the fact that when looking to purchase a brand new control unit, they are not directional and the part number is the same, so they must be identical. I've also ruled out the brake solenoid by taking a closer look at the hydraulic schematic, before the pilot oil ever gets to the control unit the brake solenoid must be engaged and the same pilot oil goes to the motors and disengages the brakes, so I know that works.