Help with JD400 hydraulic problem..

[TexasGus]

Hi.. I'm a mechanic, not a tractor mechanic so bear with me. I've been working on an old JD400 with a backhoe on it.. we've repaired leaks (fuel and hydraulics) and even put a new hydraulic pump on it (had no power).. everything was straight up and I encountered no problems.. lots of power, smooth performance.

Except after maybe 100? hours of running with the new pump the controls have gotten very heavy or stiff and when you try to move the bucket or the hoe it swings or raises wildly.. it's dangerous! so it's parked until I can figure it out.

I have the manual and I'm not a dummy (really!) but I'm stumped on how to diagnose this or what component or components may be the cause.

Any help much appreciated.

Thanks!

[banjodunn]

G'day Gus and what do the controls feel like with the engine off do they feel free and smooth? If not then you may just have linkages that are binding up.

If they feel ok then I suggest you get a pressure gauge and tap into the outlet of the pump or the inlet to the control valve and see what your relief pressure is, I don't know the figure for sure but it should be around 2500 - 2750 psi. To do this check after you have the gauge installed just operate one of the functions to the end of its stroke and hold there just long enough to get a reading.

Let us know what you find.


Jon

[Tx Jim]

banjodunn
JD 400 has closed-center hyd's therefore one can just install a gauge at the frt hyd pump and take reading without operating a hyd control function. I'm more of an agriculture than industrial equip. person but I think stand-by pressure should be in the 2250-2350 psi range.

[TexasGus]

Hey, thanks all for the tips.. When I showed up this morning to get in to it the boss said a real tractor and hydraulics shop was coming to pick that old beast up. I'm free! Still miss the opportunity to learn more about it. If and when they fix it I'll ask them what the deal was and post back.