Farmall H and M hyd pressure

marlin54

Member
I have an H and a M and checked both with a gauge. about 450 lbs pressure on each which is fine for lifting a cultivator. My question is , If I took out the pumps is there any way to get more pressure like either putting a stronger pressure relief spring behind the ball if it has a relief spring or any other way to get more pressure? I had a manual for one years ago but gave it to a friend and can't locate him . are they gear driven ? do they have a dump valve with a spring?
 
There was an upgrade to them that got up to 800 lbs years ago but I don't know what they did to get the increase.
 
I think IH used tighter tolerance gears in the pump. There is a spring loaded ball pressure relief valve in the pump.

I would have thought every H & M would have had the increased pressure pkg in it by now. I tested my Stage II Super H, live pump by distributor, got around 850 psi on cool oil, about 70-80 degrees F. Loader performance and lifting loaded wagons was never good as I thought it should have been. Should be 1200+ psi.
 
I believe this is the last relief spring part # 15258E was used in production. Messicks shows is as available for 8 and change.
 
You could put live hydraulics off a 300 or 400 on, will bolt right up if tractor is late 1950 or newer.
 
those old tractors and their low pressure hydraulics were just to get the job done. thats all they had back then. to lift a 10 ft cultivator or 3 bottom plow. even the hydraulic rams from back then were not compatible with todays pressure's., it would blow that cyl. all apart. even saw it done. then start increasing pressure in the pump and asking for trouble in the pump driving department, like camshaft gears for example.
 
It can safely be increased to 850 or 900 but I have seen pumps strip the threads when the gauge hit 1000 psi. I would compare the old relief valve spring to a new one and if significant difference is noted, just try a new spring. Make sure the relief valve seat and ball are in good condition and (IMPORTANT) gasket under the relief valve seat.

Bushings at also very important to keep gears from moving away from side of pump under pressure. Body may be worn but don't think you would want to invest in a new one even if it was available. When assembling the pump, push the body against the pressure side of gears to help reduce clearance. Later pumps had shims to adjust end play on gears. Also, all this is with a 30 wt oil, not hydraulic fluid of lower viscosity.
 

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