NH #3930 PTO HAS QUIT

[etaylor0056]

2. One is under the left hand side in the trans and other is mounted to the engine block on the right and side of the tractor.

 

[Spicer]

I am admittedly not an expert with this model, however I noticed from the parts illustration that there is an unloader valve mounted on the top front of the 3 point hitch lever casting.

An unloader valve will keep back pressure on a system, if your pump sucked in air it would lose its prime because it wouldn't be able to over come the unloder pressure.

On the NH parts site select hydraulics and the three bottom selections on the right pane.

Mike

 

[etaylor0056]

It's a highway tractor and is built like the 4110, 41 series tractor. And I think you are onto something Mike. And this is why I think so. It was Monday night when the issue occurred. I have been using it only to grade driveways and have not checked the rear housing fluid level since i bought it. So when I came back Tuesday to look everything over I noticed the dip stick had nothing on it. So after 8 gallons of hyd fluid it finally got it back up in the safe mark. But when I tried to engage the pto or work the lift it still wouldn't work. How would I bleed this system?

 

[Spicer]

First off you should limit the use of this tractor. A pump that lost its prime is essentially running dry.

From the parts diagram it appears that there are 3 hydraulic systems. steering, high flow and low flow hydraulics. The 3ph and the pto would be on the low flow hydraulics.

I would prime the smaller low flow pump by loosening the pressure side fitting on the pump. Usually the pressure side of the pump is on the bottom of the pump and the pressure side tubing is smaller than the suction side.

Mike

 

[etaylor0056]

Ok Mike. Thanks for the input. I have not driven the tractor since the fluid addition didn't solve it. I'll try and find a diagram and post it to make sure we are on the right track.

 

[Spicer]

Schematics would help greatly, there are actually 4 pumps on this model.

You could start your diagnosis by ensuring both pump are primed and pumping.
Engine Mounted Pump:
Loosen the flare fitting that is attached to part #30, start the tractor and see if oil sprays out of the fitting. If no oil is being pumped out you will have to remove filter #28, add oil inside #21, fill the filter with oil, install filter and repeat above with the loosened fitting.
View attachment PUMP ASSEMBLY %26 RELATED PARTS%2C ENGINE MOUNTED.pdf

Transmission Mounted Pump:

Remove plug #13, start the tractor and see if oil is being pumped out. This pump has flooded suction and doesn't require priming, but there could be other issues with the pump.
View attachment PUMP ASSEMBLY %26 RELATED PARTS%2C CENTER HOUSING MOUNTED.pdf

The above pump housing has 2 pumps, I believe these 2 pumps make up one 2 stage pump.


Mike

 

[RickB]

The 3ph and the pto would be on the low flow hydraulics.


Mike

Wrong. 3PT and remote hydraulics are the high pressure and flow functions. The PTO clutch is the low pressure / flow function. If both sections of the transmission pump are functioning, all tractor functions will be supplied, but remote flow will be low. The auxiliary engine mounted camshaft driven hydraulic pump only supplies additional flow to the remote valves.

 

[RickB]

The above pump housing has 2 pumps, I believe these 2 pumps make up one 2 stage pump.


Mike

Not a two stage pump, rather a two section pump with separate flow circuits, one high pressure, one low. Two stage pumps typically have a single dischare or pressure port.

 

[etaylor0056]

Schematics would help greatly, there are actually 4 pumps on this model.

You could start your diagnosis by ensuring both pump are primed and pumping.
Engine Mounted Pump:
Loosen the flare fitting that is attached to part #30, start the tractor and see if oil sprays out of the fitting. If no oil is being pumped out you will have to remove filter #28, add oil inside #21, fill the filter with oil, install filter and repeat above with the loosened fitting.
View attachment 422996

Transmission Mounted Pump:

Remove plug #13, start the tractor and see if oil is being pumped out. This pump has flooded suction and doesn't require priming, but there could be other issues with the pump.
View attachment 423002

The above pump housing has 2 pumps, I believe these 2 pumps make up one 2 stage pump.


Mike

Ok I have pulled #13 and no fluid came out of the transmission mounted pump with engine on or off. I cracked line 30 on the engine mounted pump and had a steady flow of fluid there but no real pressure And filter was also full. No air out of cracked line or filter. Now I did crack a line off the discharge of the flow control valve that is supplied by the tube leading from the trans mounted pump that leads to the oil cooler and when I started the engine up that sucker spewed oil out like crazy. Probably a gallon before I could shut it down. So that tells me that shaft powering the pump is good at least.
since 13# plug did nothing is this a sign that the other half of that pump is bad?

 

[etaylor0056]

Wrong. 3PT and remote hydraulics are the high pressure and flow functions. The PTO clutch is the low pressure / flow function. If both sections of the transmission pump are functioning, all tractor functions will be supplied, but remote flow will be low. The auxiliary engine mounted camshaft driven hydraulic pump only supplies additional flow to the remote valves.

Thanks for the help Rick, So You said if both sections of the transmission pump are functioning, all tractor fuctions will be supplied, but remote flow will be low? Is this correct. Or did you mean to say that if One section of the transmission pump has failed that the remote funtion will be low?
The remote funtion is low,weak and turns the motor on the mower bar slower than normal.
Since I got flow out of the tube leading to the Flow control valve and not #13 pug on the pump in the drawing above that its safe to say that one half of the pump is bad?