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G-MAN
10-24-2003 11:01:47
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Re: 4520 JD hyds, destroke valve? in reply to Alvin n Ms., 10-24-2003 09:11:18
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Unless your pump has a manual de-stroking screw (located on the top of the hydraulic pump), and you turned it in when you parked it, the destroking screw is not the problem. However, underneath that screw (or plug as the case may be) there is a stroke-control valve in the control block of the pump, that will stick and cause a loss of high-pressure hydraulic oil. It could easily be stuck, which isn't too uncommon on Deeres - some will just up and lose hydraulics while going through the field. On occasion, you can remove the top plug, install a manual destroking screw if it doesn't already have one, and get the stroke control valve freed up by turning in the screw. If that doesn't work, you have to remove the pressure adjusting screw and it's nut from the bottom of the hydraulic pump control block. It should be a internal hex adjusting screw. The stroke control valve is located above that fitting. There are several little pieces in there that have to be stacked in a particular order when reassembling, including a washer, spring, guide and so forth. And it's in a real handy spot to get to. The easiest way is to remove the top plug in the passage and use a piece of wire ran through the center of all the parts. It's still challenge to get everything up in there and get the bottom nut in, but it gets easier the more you do. The stroke control valve will run you around $50. If I were going to the trouble of pulling the old one out to check it, I would go ahead and install the new one. I would also HIGHLY recommend borrowing a service manual, as you will also have to readjust the standby pressure after replacing the vavle. The "destroking lever" he referred to is probably the transmission-disconnect lever that is used to disengage the clutch on the back of the flywheel when cold-starting a powershift New Generation tractor. If the tractor moves, it's working correctly, and your transmission pump is also working correctly. Replacing the stroke control valve isn't terribly difficult, but it does have to be done correctly, so you can post back or email me if you have any questions. Or, you may elect to leave it to the pros. A good tech can have that valve removed and replaced, and you back going in less than an hour.
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