Trouble shooting hydraulics

[sawmant]

Anyone know of a good resource book or guide to trouble shooting a hydraulic system on a tractor? My JD 400 hydraulics are not working, replaced pump last fall. Changed fluids and filters. I don't have gauges to test but do have parts manual and owners manual. Neither one has any detail on the operation of the hydraulics.

 

[kennyd]

Welcome to TBN

Here are two I have used: Army Hydraulics Manual and The Principles of Hydraulics

Just to be clear, are we taking about a JD400 L&G tractor or a JD400 Industrial tractor?

Edit: I just checked your profile, It is a Industrial...I believe your system in Closed Center.

Can you describe some symptoms?

 

[sawmant]

It is the 400 industrial loader, about a 1975 model. I fired up the tractor on a very cold morning and after a few minutes raised the bucket and dropped the bucket forks and the hydraulics quit like a switch turned off. The front pump was replaced last fall due to excessive leak in the main shaft seal of the old one. The rebuilt pump was an exact replacement and worked well for a couple of months. This pump has an electric destroke and did not have the manual destroke as it was originally optional. Right now nothing powered by the front pump works. In addition, the items that don't work are the power steering, three point hitch, and loader. The transmission works but is very slow to engauge. When I changed the fluid and filters the filter for the front pump had sludge in it but no metal or other debris. The transmission filter didn't have much sludge but the fluid was pretty slow flow, but it was a cool day in the upper 30's.

 

[true temper]

Look for a book called FOS hydraulics printed by John Deere. You need to make sure you have charge pressure at the hydrauic pump. There are two plugs on the right front side of your pump. The top pluc is standby pressure and the bottom plug is charge pressure. If you got a brand new pump, not rebuilt the ports will be metric, takes a 3/4" wrench. If the pump was rebuilt from an old one it takes a 1/2" wrench, which are SAE threads, I believe #3 O ring boss. If I remember right the top port should be about 2500 PSI. The bottom port should be 160 or so.

 

[mmurphy]

Saw mant, the pump in the transmission is your charge pump to the hydraulic pump, check flow there first. I am wondering about the electric connection for destroke on pump. If I remember right they were sticking when tractor was off causing hard crank on start. Just scare me and give me an idea how much that pump costed, and what size, I think they had 3 different pumps.

 

[banjodunn]

G'day don't wanna sound smart but have you checked the pump coupling to make sure it is still driving??



Jon

 

[sawmant]

The pump was $769 plus shipping or close to that after credit for return. I don't remember the number of the unit off hand, I'd have to look it up in the parts book. The drive coupling is still connected and looks in good shape and appears to be driving the pump. It looks like I'll have to get a gauge and fittings to do some testing. I'll try to stick a picture in later today.

 

[mmurphy]

The pump was $769 plus shipping or close to that after credit for return. I don't remember the number of the unit off hand, I'd have to look it up in the parts book. The drive coupling is still connected and looks in good shape and appears to be driving the pump. It looks like I'll have to get a gauge and fittings to do some testing. I'll try to stick a picture in later today.

Price did not scare me quite so bad!! Check that connection again I think it is nothing more than a solenoid, (I could be wrong, Mine does not have that)check for continuity, I would say jumper it to hear if it makes a sound , but then again if it has a diode in the circuit and you change polarity it could burn diode out. Maybe one of the other guys will have a better idea for you then that. If pump is not coming into stroke no fluid will be pumping cause swash plate will be flat and there for nothing will be moving.