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I just bought a 2005 John Deere 6420 and it has really stiff steering, and really slow hitch movement. My first attempt to resolve this issue was to drain the hydraulic/trans fluid, check and clean the sump screen, and replace they hydraulic and transmission filters. I then refilled with new JD HyGard fluid, but this had no effect on the problem. Raising to max RPM has very little effect - maybe just a very slight improvement. What would you do next?
 

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I would treat for algae.
 

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Does there seem to be a lot of hydraulic noise? COuld be hydraulic pump or a cracked rockshaft valve housing. Have seen a few of these crack.
 

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Does there seem to be a lot of hydraulic noise? COuld be hydraulic pump or a cracked rockshaft valve housing. Have seen a few of these crack.
No, not much if any hydraulic noise. It acts like the pump stays in low pressure standby mode 100% of the time and never increases flow/pressure when trying to steer or raise the hitch.
 

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No, not much if any hydraulic noise. It acts like the pump stays in low pressure standby mode 100% of the time and never increases flow/pressure when trying to steer or raise the hitch.
Don't know lots about this but perhaps the pressure relief valve would be a good place to start? If you have a guage, measure pressure against spec. Kennyd sell them if you don't already have one.

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Why? What did he write that gave the indication of algae growth in the system?
I just bought a 2005 John Deere 6420 and it has really stiff steering, and really slow hitch movement. My first attempt to resolve this issue was to drain the hydraulic/trans fluid, check and clean the sump screen, and replace they hydraulic and transmission filters. I then refilled with new JD HyGard fluid, but this had no effect on the problem. Raising to max RPM has very little effect - maybe just a very slight improvement. What would you do next?
Seems like a clogged passage or filter, new fluid and filters had little affect.

algae seems to me to be the cheapest and easiest thing to fix right off the bat. I would go with the cheapest thing first.
 

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No, not much if any hydraulic noise. It acts like the pump stays in low pressure standby mode 100% of the time and never increases flow/pressure when trying to steer or raise the hitch.
I am wondering if the filter bypass is stuck and not allowing pressure to build??

Also there are test ports on the rear (near the rockshaft control valve) for Load sense, Steering, and System pressures.
 
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Does there seem to be a lot of hydraulic noise? COuld be hydraulic pump or a cracked rockshaft valve housing. Have seen a few of these crack.
I second that, the rockshaft housing, seen that on earlier 20 series. New replacment valves are narrower and redesigned.When replacing don't miss track of the load sense discs when pulling apart the valves (small black discs half the size of a dime that fit into ressesed ports) Without seeing/testing it that's my guess, cracked valve internally leaking.
 

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Got this resolved. Pressure gauge on all 3 test ports showed good low pressure, but never any high pressure confirming the pump was not going into stroke. A test gauge in the SCV's showed 0 PSI regardless of lever position further confirming my original assumption.

First verified that all dime valves were properly in position and in good condition. Then removed the compensator from the pump and found the load sense spool valve was sticking. Gently removed it. Cleaned the bore with fine valve lapping compound/cotton swabs, and the valve with .000 steel wool until it moved freely in the bore. Re-assembled and tested. Re-adjusted pressure limit spool to 2900 psi. All good.

Thanks for all the suggestions and advice!
 

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Thanks for the follow up :thumbup1gif:

Might want to verify there is no moisture in the fluid.
 

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Thanks for the follow up :thumbup1gif:

Might want to verify there is no moisture in the fluid.
There was slight evidence moisture in the original fluid when I drained and replaced it. Not enough to gum up and clog the sump screen like I've seen multiple times on Deere compacts however. I did sorta decide that was the reason for the sticking valve.
 
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