Loader wont hold position

[Mighty Dodge]

The 420 loader on my JD 4200 started dropping a little as it it has air in the lines. It will drop about six inches then stop. This started suddenly this week. I changed the fluid, filter & cleaned suction screen last fall. I switched the lines around so the curl circuit raises and lowers the loader....same thing. It will sometimes lift very slowly until it gets about half way up then speed up. Anybody have an idea as to what's going on?

M.D.

 

[kennyd]

The seals in the lift cylinder(s) are probably starting to leak internally, not that uncommon in these loaders. They are easy to re-seal.

 

[Mighty Dodge]

Ok, I just noticed another symptom. If I just barely pull the stick back just a little the loader will drop as if fluid is bypassing through the valve. It never did this before. Still think it's the cylinders or possibly crud in the the loader valve?

M.D.

 

[beenthere]

How many hours of loader use on the 420 FEL?

Read up on the recent FEL cyl seal replacement thread, for some idea of what it entails. Is was good. I'll try to find it for you. If me, I'd chase the seals first, because it acted the same when you switched to the curl side of the valve.

 

[Mighty Dodge]

Thanx

Yeah I think the cylinders could use new seals but there seems to be something else going on also. Guess I won't know for sure until I rebuild the cylinders. The tractor/loader has 613 hours on it.

M.D.

 

[AKKAMAAN]

Ok, I just noticed another symptom. If I just barely pull the stick back just a little the loader will drop as if fluid is bypassing through the valve. It never did this before. Still think it's the cylinders or possibly crud in the the loader valve?

M.D.

I would say you have a leaking cylinder seal PLUS a worned/failing valve spool.....
A double acting cylinder with bad seal will not lower anytime if valve spool is tight...unless there is a heavy load on the cylinder.....pressure will then reach the point when then work port releif valve (if there is one) will open....

If rod diameter is half the cylinder bore diameter, pressure from load will become 4 (four) times higher, when cylinder seal is leaking....so if you have load on your cylinder you will lift it with enough pump flow, but with valve in neutral this high pressure will make cylinder drop down faster than normal....especially if you MOVE THE VALVE A LITTLE BIT!!!

 

[art]

Rebuild the valve! also try switching from the curl to the lift!

 

[beenthere]

Art
The OP mentioned right off that he switched the curl to the lift....and got the same thing.
Seems that would lead to the cylinders...not the valve. Or am I missing something?

 

[AKKAMAAN]

Art
The OP mentioned right off that he switched the curl to the lift....and got the same thing.
Seems that would lead to the cylinders...not the valve. Or am I missing something?

yes... double acting cylinder wont drop down unless valve is leaking....here is a clue.....the volume of the cylinder rod goes where???!!!

 

[kennyd]

There is no rebuilding of these valves...The spools are a lapped fit and only sold as a kit that includes the valve body.