JD400 Backhoe hydraulic oil flow seems reversed?.

[veewee]

My unit is running out of hydraulic oil in the implements, with violent shuddering and then no movement either end. I have got it working for a few minutes by filling the header tank situated over the main pump, enabling me to get it back home. Since then I have replaced the transmission filter and cleaned the mesh screen and also replaced the hydraulics filter. All valves were removed and checked for cleanliness. I also checked the valve located in the trans. behind a plug which is forward of the dipstick. Next the valve body end cover was removed (6 Allen head screws) and all drillings checked, as were the 2 lower piston valves. The upper valves appear to be accessable only after the valve body is removed. After filling the trans. with oil I disconnected the pipe coming off the top of the hyd. filter base (connected by a short flexible hose )and joined to a T junction at another pipe which goes back to the valve body in one direction and to the main pump in the other. The motor was started and oil flowed from this pipe into a tub OK. Next test I disconnected the right angle rubber hose that connects to the reservoir above the main engine driven pump and inserted a 3/4 inch pipe into this to flow into a tub, expecting that oil would pump up through the oil cooler and into the reservoir, but the reverse happened and oil poured out of the reservoir and covered my engine, firewall, seat etc. What a mess, helped along by the fact that the fan blades were spinning! I obviously don't know the oil flow routes or where to look next, so any help would be much appreciated. As an aside, when I had the valve body end cover off and was cleaning it I removed a screw on the edge of this cover and discovered it was a tapered needle valve , just like a fuel adjustment valve in a carburettor. How do I determine the adjustment for flow? I'm now at your mercy!

 

[Tx Jim]

Sounds as if you don't have a JD service manual!!! If not you need to acquire one as closed center hyd are complicated to the inexperienced technician!!! Oil reservoir by radiator is filled from excess trans pump output after lubing trans & powering reverser BUT not filled by main hyd pump. Sounds as if your tractor has a large internal hyd leak. Try a test by disconnecting power steering supply line and capping it then operate tractor with manual steering to see if hyd will function correctly.

 

[veewee]

Somehow I'm messing up sending my comments, but I'll try again. Tx Jim, your test as detailed above worked, and implements operate as they should, but of course I don't have power assisted steering. What does this result tell you regarding the fault in my hydraulics? Thanks for shareing your knowledge.

 

[Tx Jim]

I don't have power assisted steering. .

Are you stating your 400 has manual steering IE no power steering??

 

[veewee]

No, what I meant was that the implements now work but I don't have the original power steering to manouver it around, and I guess that if I reconnected the hydraulic line then I would be back to my original position with non functioning implements.

 

[Tx Jim]

Sounds as if the power steering valve has one or more of the 6 large o-rings that has failed. Although tedious to replace these o-rings can be replaced while large PS housing remains attached to tractor.

 

[Tx Jim]

Sounds as if the power steering valve has one or more of the 6 large o-rings that has failed. Although tedious to replace these o-rings can be replaced while large PS housing remains attached to tractor. Seal kit part number is AT26188

 

[veewee]

I have now removed my power steering shaft and housing and there aren't any O rings on it, just 2 large ones on the lower section that is exposed when the casing is removed. I checked the JD parts website and my PS appears to be shown as Catalog 973, Grid 117, Section 45, Page 6, except mine didn't have Key 21, a spring. What I did discover when this shaft assembly was removed was a heap of mutilated shims, probably the .002 ones referred to in the parts list. As I cannot find anything to account for my problems, like a failed O ring, I'm wondering whether these shims could be the reason for my problems. Also what clearances are they meant to be set at, as they are on the ends of both valve bodies?

 

[Tx Jim]

There is/was 6 large o-rings that fit in the power steering housing casting. 3 large o-rings for each of the 2 operating valve assemblies.

 

[veewee]

You are so correct again TX Jim! i didn't look closely at the housing internals but, as you advised, there were some O rings and the remains of others in the bottom. I now have the replacement 6 O rings and just have to get the old ones out, which is proving quite tricky for the bottom 3. Is your library of information able to give me a clue as to what clearances to set for the multiple shims on each valve body? Thanks so much for your patience with my many requests.