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I'm not familiar with the hydraulics on the 2020, so my first question is, is this your pump:
787910

If so, the eccentric lobe on shaft #41 will need to be machine ground smaller! Not knowing what/why you want this, other options may be a flow control valve or a pressure control valve. Depending on how the pump is driven, operating at a lower rpm will also reduce the flow. I think more info is needed for a more precise answer! Bob
 
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Flyweight and Tx Jim,

Is this the same feature that was an option on my 3020 for cold starting that it allowed it to turn over easier not turning the big pump with flow. Could it be turned down enough to allow for power steering and perhaps a slower speed on the three point and lower flow on the aux ports yet not harm anything? Just wondering if that would make it quieter because that pump really whines.
 

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You're correct destroking screw was designed to stop frt pump from attempting to pump oil therefore putting less load on starter while attempting to start engine . DS is either engaged or disengaged no lowering of pressure. Hyd stand-by pressure can be lowered by adjusting screw under the bottom of pump CCW. My guess is lowering stand-by pressure won't stop pump whining. How long since hyd filter was changed & sump screen checked/cleaned?
 

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Bob
I'm going to post a reply to your statement explaining how closed center hyd pumps are designed to operate.
[/quote]If so, the eccentric lobe on shaft #41 will need to be machine ground smaller! [/quote].
I've never heard your theory of machining pump shaft(key 41) before your post. IMHO machining lobe on shaft wouldn't lower pump pressure but would lower GPM output of pump because of lowering distance pistons travel in pump housing bores.

Closed center hyd pumps similar to the parts schematic you posted build hyd pressure & store pressure in the hyd lines which normally on this model is 2250 psi which is commonly called stand-by pressure. When stand-by pressure is achieved the stroke control valve in photo below opens sending high pressure oil into pump crankcase which pushes all pistons away from rotating shaft(key 41) which causes pumping to immediately cease. When hyd pressure lowers in crankcase springs force pistons back against rotating shaft & pumping commences. Clear as mud!!
Jim
 

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How long since hyd filter was changed & sump screen checked/cleaned?
I appreciate the explanation. Changing suction screen and filter along with cleaning the bronze filter that is in the pump itself made no difference. It’s not a big deal I was just curious.
 

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Tx Jim, Thanks for the explanation. Clear as mud or not, I TOTALLY now understand what's going on inside the pump. I was unaware of the destroking valve apply pressure to the pistons and moving them away from the eccentric. Thanks again, Bob
 

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Video of the JD closed-center hydraulic system from back in the '60's.




Below is a break-down of the most commonly used pump on early model JD utility tractors.

 

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You're Welcome.
There is incorrect information given in the 1st video flyweight posted. Video stated several times that this closed center hyd system required only 1 hyd pump. In reality the frt piston can't suck oil & must have oil supplied to it which is one of the tasks of the trans pump.
 
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