4020 no hydraulics

Merc

New User
Everything worked fine. Sat for two weeks, started and slow hydraulics. Then, after a minute or so no hydraulics. Tractor gets serviced religiously. Only maybe 30 hours since hydraulic oil change, along with suction screen cleaning (no junk in it) and filter change. I know there is a booster pump in tranny to feed high pressure pump on front of engine. Heard of "destroking" pump with special tool from JD. Also something about a check valve in system somewhere that hangs up. All input and experiences welcomed. Don't want to start just throwing parts at this. What is good way to narrow down the problem, or has anyone experienced the same issue and know right where to go? I read in this site quite often, and you guys are the most knowlegable people out there.
Thanks for any help.
 
This is how I would start. I would check trans pump drive shaft first, remove top link bracket on rear of tractor, you should see a flat nut remove and pull hex shaft out, check to see if stripped where it goes through pump, if so replace and try hydraulics again
 
(quoted from post at 16:19:39 10/19/14) This is how I would start. I would check trans pump drive shaft first, remove top link bracket on rear of tractor, you should see a flat nut remove and pull hex shaft out, check to see if stripped where it goes through pump, if so replace and try hydraulics again

4020 has no hex trans pump drive shaft to strip out.
 
Yessir. Did that already. Ran it for a few minutes several times around half throttle. When it's cold, slow for a minute, and then they quit.
 
I did check that pump coupling was not slipping right away. That happened to me once before on the other 4020 I have. Everything is tight and turning fine.
 
When they set a while the charge oil leaks off, and it's very normal to start an engine while holding the clutch pedal down, and on this tractor that means the trans pump is "not" turning, and "if" you set there waiting with the pedal down,,nothing happens....till you release the pedal and let her catch up with the charge oil,,, hopefully this is all that is wrong,,,if it still don't come to life then the trouble shooting starts to gather...
 
Okay,, then all the easy stuff is out of the way....now since all the visual things are looking right,, I'm thinking the stroke valve may be stuck,, and letting her run for a bit "may" let the stroke valve get right,,some times backing it out and running it back in will help that too, it's kinda nasty to get to,,up under the front,,3/4" wrench to back the jam nut off and an Allen wrench to work the screw,,a pressure gauge in the coupler to make sure it's back to 2250psi when your done,, a gauge in there right now will read near nothing..
 
It has never given any issues like this before. My starting sequence usually does not have me with foot on clutch, just a double check it's in park, and fire her up. Usually hear a little pump chatter for a few seconds, then everything kicks in and works fine.
 
I did that, but in wrong fashion. I loosened the 3/4nut and tightened down with allen wrench, not loosened up. I should have mentioned that one. Anyway, it got worse so I backed out of it, but not all the way
 
Look closer at your front drive shaft,,"if" the spline stripped out on the pump end of the shaft it's hard to see if the pump is actually turning, some times I put a dab of paint on the pump shaft to see if it's turning,,I have seen the coupler shaft strip out clean and not make a noise...
 
Will check it out closer. Pretty certain it was all good. A few years back I replaced the steering valve/ column, and pump pressure was low at 1500 or so. I did not turn it up, because everything worked just fine, and I was scared to hit the old thing with a lot of pressure.
 
You were thinking in the right direction,,with all the different models and issues it's a good thing there are so many helping on here...
 
(quoted from post at 17:13:48 10/19/14)
Next thing I suggest is check the hyd filter relief valve to be sure it's not stuck open.
here and how do I go about that? This tractor has worked slick as a whistle for many moons. It puzzles me that it worked fine when I shut it down. Started it up two weeks later, and it was done.
Thanks for the help.
 

Check to see that valve(parts key 50) isn't stuck open.
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Will check that out soon as I can. Tractors in field an hour
away from house. I'll get back with y'all after a few closer
inspections. A big Thanks to all.
 
If you are sure the pump is turning, I'd try to
verify the pump is at least getting a little oil
from the trans-pump. Easy to check by unhooking
the line, cranking the engine, and see how much
comes out. One gallon in a bucket in 20 seconds
with the engine idling is plenty. If you have that
much oil - pull the stroke control valve out and
check it for debris. One piece of crud stuck in it
will stop all the hydraulics from working.
 

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