[Josh heatwole]

Hi I am new to this but I have searched high and low looking for answers to my problem but cant seem to find it. My 400 just randomly lost hydraulic power in the middle of using it. It leaks some oil and normally when it gets low it whines but I refilled the oil but it will not build pressure. you can see it attempt to move forward and reverse or lift the blade on the front but can't. It seems like what people are saying a charge relief valve stuck but I cant for the life of me find that on my machine. The John deere parts page shows it on the left side of the pump housing but mine doesn't have anything there. I have changed the filter, checked to make sure the little pin inside the pump gear isn't sheared, and taken the relief valve out of the valve bank and checked it but still to know avail. any help would be appreciated. Thanks

 

[Josh heatwole]

Josh,
Welcome to the group, and particularly to the "black sheep squadron"--so named by another JD 400 owner for some of the unique features of this venerable tractor. Where is your hydro leak? I'm wondering if that leak is related to or the cause of the problem. For example, if there is a leak in the hydro fluid pick-up tube (big elbow tube coming from the transaxle reservoir to the tranny), the pump will pick up air causing foaming in the fluid and weak hydraulic function. Also, check to be sure one of the implement spools is not stuck at its limit. Work all three levers a bit and convince yourself all three are returning to center. A stuck spool will steal fluid from the power steering and other circuits, and affect transmission speed (although I have not seen a fully disabled transmission).
Harold

the leaking is just from cylinder hoses or cylinders that just need to be rebuilt. the reason it seems like a stuck relief valve is because the tractor was working flawlessly and just instantly lost pressure its not something that began to slowly happen. I checked all the spools multiple times and you can hear opening and closing theres just not enough power there to make it work. Does the 400 not have a charge relief valve like the others show on the parts page?

 

[Josh heatwole]

Josh,
From the symptoms you describe and the checks you have done, it is logical to question a relief valve. There is no relief valve in the hydro pump--just a cone on the left side and a plug on the right side. The system relief valve (also described as a bypass valve) is located in the front of the implement valve body. You have seemingly checked this assembly to make sure it is clean and that the spring is intact. Charge pumps do wear out, but it makes no sense to have one fail suddenly. Do you have a hydraulic pressure gauge to measure pressure at the front quick connects? Does the on-board hydraulic cylinder work to lift the mower deck (if attached) or 3-point hitch? Does the power steering work? If you activate an implement lift valve or power steering with the hydro lever in the forward position, does the tractor move? Is there any chance that the driveshaft front key or engine flywheel key sheared and the drive system is slipping as any load demand is placed on the transmission? (You had presumably removed the driveshaft back end and key to check the charge pump pin, so there should be no issue there).
Harold

So I put a pressure gauge on one of the remotes and with the engine revved all the way up it reached 80psi. yes i removed the bypass valve twice and checked it. i put an extra spacer in it and i noticed a very small change in its pressure. I did notice when i tried to go in reverse or forward and at the same time activated and implement valve it did seem to help it go forward/backwards better but still not enough to drive unless on concrete. and yes i double checked the drive shaft and it is tight. it just seems like there must be a blockage or something but i just haven't been able to nail it yet.