Posted by JDseller on February 14, 2012 at 20:19:30 from (208.126.196.144):
In Reply to: 401B john Deere posted by Ken Midlam on February 14, 2012 at 09:03:29:
Ken: I would recommend that you get some one that understands John Deere's hydraulic system to help you find out what is wrong before spending a lot of money on "the hydraulic pump". There are many things that can cause the system not to have any pressure. So you could change the main hydraulic pump and still not have any system pressure. You need to give us a little more information so we can help. To really diagnose the problem you need to check the charge pressure and the system pressure and flow. It would be very hard for us to walk you through it on this site. It really needs to be done in person or you need a service manual and some knowledge.
A short over view of the system: The transmission/charge pump moves hydraulic oil from the transmission/rear end sump to the main pump at 150 to 175 PSI. This transmission pump is a simple gear pump that just pumps when running. There is valving after it to control the pressure and flow. The main pump is a close center constant pressure pump. That means that even if you are not using any hydraulic oil any where it still has full system pressure (2000-2250 PSI) on stand by but at zero flow. Then down stream from it are the hydraulic systems that use oil: Steering and brakes have first priority, then it goes to the three point, selective control valves, loader valves, or back hoe. Depending on what your 401B has on it. It could have a combination of all of them.
So you could have a bad transmission pump so you have no charge pressure. The pressure control valve could be stuck and not allowing flow to the main pump. The stroke control valve could be not working at the main pump making it not pump any flow. The main hydraulic pump drive coupling could be sheared so the main pump is not turning. The priority valve maybe stuck and not allowing anything but steering and brakes work. The pressure relief valve in the three point could be stuck and dumping all of the system pressure and flow back into the sump.
I will stop there as it could be many different things causing the system to not work. I wrote all of this because you did not tell us if you know what the problem is for sure. Changing just the front pump is not that hard but usually you don't just change them without other problems needing fixed too.
To change the front/main hydraulic pump on a 401B industrial you will have to remove the radiator and take the pump out the top. The Ag tractors can be taken out the bottom with the front axle removed.
If the transmission pump is the problem then the tractor will have to be split. We need more information to help you. The hydraulic system on a JD 401B is a complex system that works well but can have many things cause it not to function correctly. So seldom it it just change a pump to fix it.
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