Ford 4400 Hydraulic Help

Ford 4400 with front hydraulic pump and loader. Something is wrong with the hydraulic system, i am fairly new to the hydraulics and need a little guidance. The hydraulic system quit very suddenly not a slow failure. Once it went out it wouldn't move the loader, or even think about moving the loader like i had 0 or near 0 pressure. I took off the main "in" line at the valves, when the engine is turned over it squirts fluid out with enough force to push my hand off the line. What i need to know is how the bypass system works on these models. Does the pump have its own pressure relief or is that in the valve block. Basically i need to know if my problems are at the pump or in the valves. My plan is to test the pressure by putting a gauge on the end of the main "in" line and turn over the engine. If i get good pressure then its the valves, if not its on the pump end. However if the pump does not have its own pressure bypass im not sure what will happen when i block off the line and turn the motor over, dont want to strip splines. Another option if the pressure relief is in the valve block is to remove the return line and turn over the engine. If fluid comes out then the pump is atleast putting out enough pressure to open the bypass and the problem is probably the valves. Not sure what that pressure is though.

If anyone can either confirm my thoughts or correct them it would be much appreciated.

The relief valve is in the control valve but that is probably not your problem. Most likely the splines are already stripped.

Mark

If the splines are already stripped then i would need to replace the pump and the valves or relief valve? If the relief valve has failed once to strip splines it would just happen again right?
If the splines are stripped is there a way to just replace the teeth or connectors or will that require an entire new pump?

When the spines strip, the pump will not turn under load. check the shaft between the engine and the pump.. and the front shaft on the pump....

paint a dot on the pump shaft. have someone operate the loader and see if the pump shaft is slipping.. there you will find the problem the spines on the pump or the drive shaft are worn down and slipping under load.

(quoted from post at 06:37:11 07/19/15) If the splines are already stripped then i would need to replace the pump and the valves or relief valve? If the relief valve has failed once to strip splines it would just happen again right?
If the splines are stripped is there a way to just replace the teeth or connectors or will that require an entire new pump?

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The splines will wear from normal use and if you are lucky the splines on the pump shaft will be ok and you just need couplings and the intermediate shaft. Not very likely that there is anything wrong with the control valve or relief valve.

Mark

How would one go about testing the relief valve. No sense in
repairing the pump if I can't garentee it won't break again? Are
there cheap pressure relief valves I could put in line so as to
double the protection in case the valve is bad?

The relief valve needs to be tested with a pressure gauge but I don't know why you think you need to add a second one. If the relief valve failed causing your problem it would most likely be a broken spring and you would just replace the spring and adjust it to the proper pressure. If you have stripped splines in the pump drive line the relief valve most likely had nothing to do with the failure unless somebody adjusted it to high. You need to find out what failed and get it repaired before you can do any testing.

Mark

So if the valve failed it would fail in the
open position, not closed? I'm just trying
to understand what will happen if I fix the
pump what will happen if the valve was
broken.

If the relief valve failed it would be open or open too easy causing a loss of pressure.

Mzrk

Next question, how does one get access to the front crankshaft pully and hydraulic pump...its pretty buried. What is the approach people use to get access? My thoughts are take off the radiator, shrowd, grill. Looks like the other option is to come at it from the bottom which does not look easy.

The first thing is to remove the pump and slide the shaft and coupling out to see what needs to be replaced.

Mark

I believe I have found my issue. Took the return line off of my valve block and started tractor. No fluid came out so it wasn't making enough pressure to open the bypass. Took off the front cover of the tractor, drained hyd fluid, and removed pump. There is a coupler that goes between the pump and the splined shaft, one side of this was stripped. From what everyone has said I guess this just happens once and a while? I will replace the coupler and reassemble. Are there any special instructions for bleeding the system and or reassembly?

Thank you all for your help.

(quoted from post at 13:59:44 07/19/15) I believe I have found my issue. Took the return line off of my valve block and started tractor. No fluid came out so it wasn't making enough pressure to open the bypass. Took off the front cover of the tractor, drained hyd fluid, and removed pump. There is a coupler that goes between the pump and the splined shaft, one side of this was stripped. From what everyone has said I guess this just happens once and a while? I will replace the coupler and reassemble. Are there any special instructions for bleeding the system and or reassembly?

Thank you all for your help.

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No need to bleed the system. Just put it back together and fill it with oil. The system will purge the air as you use it.

Mark