Cat D3G LGP serial #BYR01624. While operating the left track stopped working. You can get it to creep along, but once it reaches a certain speed it throws the parking brake on. If we stay under that speed we can barely limp along. We managed to get it back to the shop. The machine is throwing no codes. We started by pulling the sun gear and were able to test the parking brake switch for function. It functions normally. We then removed the final and found no abnormalities. No metal was found in any of the fluids. We went deeper and removed the drive motor and inspected. We did not take it apart, but no metal was found and the shaft will spin with some effort by hand and makes no noise. At this point we reassembled the drive motor and finals. No change, but we didn't expect any. At this point we had been sure we had some sort of mechanical/gear issue but that was ruled out. We then downloaded the Cat SiS2go app and poured through the manual. We found the test port instructions (also linked in other threads here) and tested the ports. Pump 2 is within spec. Pump 1, the left side drive pump, is showing less than 12psi. We have not gone to the extent of the messy job of removing the hydrostatic pump yet. We are toying with the idea that we might have a stuck relief valve. Anyone have any more clues before we dive into this tomorrow?
Well, this is what is wrong. Pump 1 broke a gear. We're going to take apart the rest of it tomorrow and see how far it goes. We're also going to remove the drive motor and clean it thoroughly hopefully it was a catastrophic instant break and didn't send much metal downstream. Center shaft kept rotating to drive pump two.
Final notes on this whole thing. You can pull the pumps out without removing the engine, but getting them back in is way easier if you just remove the engine. I suggest just pulling the engine from the get go, because you are going to want to replace the plastic pump driver gear on the back of the engine anyway.