401B john Deere

Can anyone tell me how hard it is to put in A hydraulic pump in a 401B John Deere tractor

Which pump?? Trans or frt hyd pump? Why do you want to replace the pump????????

Hyd as it does not work

Not working can be a problem with either pump. Deere piston pump in front must be fed oil by a gear pump in the transmission.

Front pump change in that machine is likely to take you half a day. As I recall, easiest with a 401 is to take the radiator off. Then the pump comes out.
Haven't done in one in many years. I pulled the pump in my 300B and taking the radiator out made things much easier.

What is it doing and not doing? What did the filter and screens look like.what is the trams oil pressure. How many gallons per minute flow to the front pump inlet? Has some body changed or worked on a valve? We regularly have people change good pumps and the system. Still doesn't work.

I agree several things can contribute to a non working closed-center hyd system besides a faulty hyd pump. 2 contributing things to hyd failure are internal high or low pressure LEAKS. Diagnostics are needed before a hyd pump is R&R'd

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.

(quoted from post at 23:19:30 02/14/12) 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.


The pressure relief valve in the three point could be stuck and dumping all of the system pressure and flow back into the sump.

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JDseller
I agree to diagnose & repair a closed-center hyd system some prior knowledge is very helpful. IIRC there is no pressure relief valve in the 3pt. There is a thermal relief valve which may be what you're referring to. There are 2 valves that control the 3pt,one is pressure and the other is return both with history of being prone to leaks.

Does it have reverser?

The valve in the end of the three point lift piston can be called several things: Thermal relief valve, pressure relief valve, etc. It does not react to heat it just allows allows the system to relief pressure if it get too high. That can be from heat expansion . It usually is from a spike load on the three point. Like bouncing a set of plows when you hit a bump with them up. I have seen them stick open and then if the operator does not know any better and leaves the three point control lever in the up position then it will dump oil right back into the sump. I know it is not a common thing. I just included it to show that there are too many things to diagnose in an email.

In all my years working at a JD dealership I don't remember replacing a AT21781 thermostatic control valve on a JD utility tractor from failure. Normally it was the RS control valves causing spraying inside RS cover.

I never had one go bad until about ten years ago either. I have had about one a year since then. The only thing I can think of that would be causing it is moving large round bales. A 5 x 6 bale of alfalfa hay can go close to a ton. These guys will take a three point mover on a JD 2020 (or other similar tractor), without any front weights. They just ride the wheelie to get through the mud/snow etc. Some of these guys are nuts on how they drive them.

You are right in that it usually is the orings/backup rings around the control valves that are the most common three point leak.

My MAIN idea in my posting was to get Ken to make sure his pump was the cause of his problems. You and I can argue all day about the fine details of each other's postings. You see break downs in TX that I don't see here. I have repairs that you don't see there.

As far as the AT21781 thermostatic control valve. I must not be the only one needing them. John Deere still has them in the warehouse and you can still buy one. If they never sold one then they would drop the part.

Also the "thermostatic control valve" is just a pressure relief valve. Temperature will not open it unless you have the lift piston clear full of hydraulic oil and heat makes the oil expand therefore building pressure.

(quoted from post at 03:04:07 02/16/12)

You are right in that it usually is the orings/backup rings around the control valves that are the most common three point leak.

My MAIN idea in my posting was to get Ken to make sure his pump was the cause of his problems. You and I can argue all day about the fine details of each other's postings. You see break downs in TX that I don't see here. I have repairs that you don't see there.

As far as the AT21781 thermostatic control valve. I must not be the only one needing them. John Deere still has them in the warehouse and you can still buy one. If they never sold one then they would drop the part.

Also the "thermostatic control valve" is just a pressure relief valve. Temperature will not open it unless you have the lift piston clear full of hydraulic oil and heat makes the oil expand therefore building pressure.

Click to expand...

As far as JD stocking a AT21781 valve that is no indicator it's a fast moving or regular selling part. JD stocks 2 cyl parts that I'll bet aren't daily sellers. I never indicated no valves were sold as I replaced some as a cautionary thing so as not to have to "re-lick the calve" JD named the valve thermostatic not me. And yes heat can cause it to open hence I guess it's JD NAME. They're are several dairies in Tx that feed large sq's of Alfalfa. I've got a large dairy just 3 miles from me.

Finally I totally agree it's much better to diagnose the hyd system that throw high $$$ pumps at it.