At my school we have a 70s (possibly) Case 450B bulldozer and the blade doesn't work any more. my teacher thinks that it might be the hydraulic pump but I'm unsure. so if any one has any thoughs on what might be wrong would be helpful.
I would have though someone would check to see that it had hydraulic fluid in the tank and the shut off valve was in the on position. After that you need to go to the pump it will be in the front driven off the crank shaft. There are U-joints that might be broken and the pump is not turning. There is also a valve on the output side of the pump (smaller line) that allows the fluid to be pumped back to tank if there is no demand for pressure IE: trying to move the blade. There should be a test port on the pressure side on the hydraulic system you will need to look for that I'm not sure if it will be on the hydraulic valve at the pump or at the 4 way valve which the hand control go to. Pressure under no load should be about 50 lbs but you will need a gauge that can handle over two thousand pounds which is what it should pump before the relief valve comes in. It is not likely that the pump is so far gone that it will not try to move the blade so do the easy things first like make sure the oil is on and that the handle is connected to the 4 way valve then check the drive shaft to the pump and the dirverter valve on the pump. You may need to remove that valve to inspect it. There is one more thing that will stop the blade from moving and that would be the packing in the hydraulic cylinder. If it is bad enough in one of the cylinders the fluid could be just pumped back to tank. You may be able to find that out with a stereoscope by putting it on the cylinder and listen for fluid movement on each cylinder. In fact if there is enough fluid movement you could feel it with your hands. You do know someone will have to hold the handle in the up movement.
