Mahindra 4005 hydraulics

[SPYDERLK]

It has about 800 hours. Too few to have the pump to fail but when I changed the fluid the first time I noticed a fair amount of metal on the screen. My thoughts are that the rapid leak down must be due to internal failure of the pump or failure of a pressure relief valve. There is a fast, slow control on the hydraulics which I would think acts as a pressure relief valve. I've cleaned it and set it to the fast setting and it has made no difference. I don't think it is the pressure relief on the loader since the three point lift and auxillary hydraulics are affected as well. Any other things I should check before changing the pump.

Thanks
Don

Are you curling you bucket to the stop or extending a cyl all the way and holding the valve on to make your pressure readings? Leak down of a loaded cylinder with valve centered is a valve problem - control valve not relief valve. The subsidence of pressure you describe, if I understand your method of taking the reading, may be just a sticky relief valve.
larry

 

[dnetherland]

Galen and Larry thanks for your replies. The way I measured the pressure was to disconnect one of the loader lines (the one that extends the cylinder fully). I then moved the joystick to raise the loader and held it in position. The pressure guage would then read about 1800 PSI and quickly leak down to 800 or so. I then plugged the gauge into the auxillary outputs and moved and held the valve engaged. Same results--pressure went to 1800 PSI then quickly drifted down. Anything else I should check. I'm not sure exactly what the pressure relief valve on the loader looks like. How should it be cleaned and how should it be adjusted when replaced?

Thanks
Don

 

[SPYDERLK]

The relief valve on my 7520 is on the loader valve...and another on the valve for the remotes. The one at the loader is primary since it is 1st in line and controls pressure to the loader as well as to the "power beyond" output which feeds the remotes and 3PH. It is externally visible - - an allen head setscrew with locknut. I have never had to clean mine, but that is where I would start because it is the only thing that would make sense to me considering your symptoms. I cant see those symptoms coming from the pump. More like a broken PRV spring on the loader valve ...
larry

 

[dnetherland]

Just to update, I removed and cleaned the pressure relief valve on the loader control valve. I then plumbed a T fitting inline between the pump and the loader valve. Same results. Pressure would go up to 1800 and rapidly drift down when holding the valve open. I was able to adjust the pressure relief valve but if I adjusted the pressure over about 1200 then it would rapidly leak down. With the pressure set at 1200 pressure seemed to hold. I'm still not sure if this could be due to a bad pump but I am starting to suspect the pressure relief valve. Any suggestions?

Thanks
Don