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John Deere Tractors Discussion Forum
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Excessive hydraulic Pressure

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Alex In Texas

01-09-2007 18:57:41




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My dad and I recently replaced the hydraulic pump on his early 410 backhoe (earliest version of the 410 series). The remanufactured pump that we installed builds up way too much pressure and will choke down the engine severely if you are not continuously moving the loader/backhoe/outriggers/etc.. It even blew a hydraulic hose. Is there some way to adjust the pressure on these pumps? Any suggestions will be greatly appreciated.

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Roy Suomi

01-10-2007 15:42:55




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 Re: Excessive hydraulic Pressure in reply to Alex In Texas, 01-09-2007 18:57:41  
Cut off an allen wrench so you can get it into the "set screw"...Back off the jam nut and back the adjustment screw a couple of turns...There are either 1 or 2 plugs on the side of the front pump cover on the starter side..The upper one is main pressure [ stand-by pressure ]. The lower one is the charge pressure from transmission pump. Put a 3000 lb. gauge into the upper port. Read the pressure without moving any hydraulic function..Should read 2300-2400 psi..If it's low , turn the bottom screw in and watch the pressure rise till you hit 2300-2400..Lock down the jam-nut when you're done..This system is supposed to maintain stand-by pressure at all times when you're not using the hydraulics..If memory serves , I think the allen wrench size is 3/16"....

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Flatls

01-09-2007 22:52:13




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 Re: Excessive hydraulic Pressure in reply to Alex In Texas, 01-09-2007 18:57:41  
The bypass should take care of that amount of pressure buildup.
I've seen pump shafts break under those conditions. Have a mechanic check it out before serious damage happens.



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G/MAN

01-10-2007 10:56:01




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 Re: Excessive hydraulic Pressure in reply to Flatls, 01-09-2007 22:52:13  
Bob is correct. Relief valves in closed-center systems are there only for safety. Oil continually going to relief with overheat the oil and cause damage. Pressure in closed-center systems is normally regulated by controlling pump output, as it is in this case.



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Bob

01-09-2007 23:40:52




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 Re: Excessive hydraulic Pressure in reply to Flatls, 01-09-2007 22:52:13  
Flatls,

It's a CLOSED CENTER system. The pressure is set at the stroke control valve on the pump.



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Bob

01-09-2007 20:05:41




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 Re: Excessive hydraulic Pressure in reply to Alex In Texas, 01-09-2007 18:57:41  
There should be a pressure adjustment screw underneath the stroke control valve at the front of the pump. If the stroke control valve has a destroke screw at the top, the pressure adjustment screw will be straight down below it, screwed into the BOTTOM.

You will need a hydraulic gauge of adequate pressure rating to see what is going on.



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Alex In Texas

01-09-2007 20:31:21




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 Re: Excessive hydraulic Pressure in reply to Bob, 01-09-2007 20:05:41  
I looked at it again and it does not have a "hand turn" stroke control screw or cut-off. On the very bottom of the pump it has what appears to be a set screw with a stop nut on it. I am guessing it might take an allen wrench to adjust it, but I can't get a wrench to it without removing the pump. I can't even feel the end of it with my finger. There is about 1/8" clearance between it and the lower tractor frame. Surely the engineers would not have been sorry enough to require removal of the pump to adjust pressure?? But that is the only thing I see on the bottom of the pump, so I am afraid the engineers may have let me down on this one. Does it normally take an allen wrench to adjust that, because it simply looks like a piece of threaded stock with one set nut on it, and that is all I can tell without removing the pump. Thanks

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G/MAN

01-10-2007 07:50:47




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 Re: Excessive hydraulic Pressure in reply to Alex In Texas, 01-09-2007 20:31:21  
Yes, that is the screw for adjusting the standby pressure. The pump maintains a constant pressure in the system at all time, and that screw adjusts it. There should be a pressure port at some point in the system to plumb in a gauge. Heat the oil, and use that screw to adjust the pressure to the proper spec. Screwing the center screw in raises the pressure, screwing it out lowers it. Standby pressure should always be checked and adjusted when installing a new or rebuilt pump.

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Tx Jim

01-10-2007 04:27:53




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 Re: Excessive hydraulic Pressure in reply to Alex In Texas, 01-09-2007 20:31:21  
I'm not familiar with industrial JD's as I worked for an Ag dealer. JD AG utilities are very similiar except of much heavier frt axle on indust. models. The allen screw is the adjustment for pressure and I adjusted them on AG tractors. I think one had to remove a tin plate to access but it's been many yrs ago. Tx Jim



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