D17 Series 4 lift arm/hydraulic issue

I have a D17 Series 4 that I just purchased and I cannot get the lift arms to work.  What could be causing this?   how should I diagnose the issue?

yes,  they are stuck in the up position and I cannot get them down.  It sounds the the control valve body next to the seat is also making an erratic noise of some type. 

I will give it a try this weekend.   This is very helpful.  I have not used this site very much but have found this a great tool.......

I got anxious to check into this and pulled the cap as you mentioned.  It is the one closest to the fender.  Sure enough,  it was pushed back so I removed the spring and took a punch and pushed it forward.   I then tried to move the lift arms and I had the back two levers  all the way forward.  I discovered that the front outside lever next to the fender is stuck forward and I tried to drive it back and it appears froze up.   I removed the other 2 aluminum caps on the back of the control valve and noted that they have a spring and a screw adjustment of some sort.   I remembered what my dad taught me - "don't F with it if you don't know what it is for."   So,  do you have other advise for me concerning how to free this plunger that the outside front lever controls?   How hard is it to remove the cover above the control value.  That way it would be easier to get to and maybe I could work the plunger back and forth and loosen it up?  Not sure what the seals will be like if it has been this way a long time?    Could this of caused damage to the pump being stuck like that?  One more thing I found out.   I tried to run it with the aluminum caps and oil squirted out the back side of  the one value that is not stuck.  Is that normal or is there a bad seal on that plunger.   On the back of the caps there is a hole with a rubber seal and they are deteriorated and the one is totally gone.  I am keeping a positive attitude and hoping for the best.   What would be the worst case scenario?  Are these control valves rebuildable?   thanks for any help you can offer.    I have asked alot of questions but figure it would be best vs. going back and forth.

I just checked the lever that is not working (tall outside lever for lift arm) and the pivot point is good and linkage looks fine.  I only have 2 front levers and 2 rear levers.   I put the rear ones forward as you advised.  The short front lever (closest to the seat) works well and I can feel the  positions you mention above.  The issue is definitely at the spool and I sprayed WD-40 on it earlier when I worked on it and I can now get it be move in and out but it takes great force to do so and I cannot differentiate any positions like the short lever.   I assume I am going to have to address this somehow?   Is this something that can be addressed without tearing things apart?   As hard as it works  I am not too hopeful that it will eventually move easier-barring and Act of God.    It is hard to get to without taking the cover off the top of the spool.   Anyway to work it back and forth to free it up from the aluminum cap end?   i will await your direction and proceed from there.     I really appreciate all your help.   btw:  my dad was a farmer and my brother still farms the 2 farms my parents owned.  They are both gone now.   Dad bought a D17 in 1962 the year I was born and traded it in on a 185 in the seventies.   I located that particular tractor but the farmer who bought it from the dealer still uses it daily and will not part with it.   I learned to drive on the D17 and wanted to get one for sentimental reasons and I also have a small farm that I want to use it on.   My father had several different AC's  and also used Gleaner Combines.  He did alot of custom farming.    His 175 had the typical 3rd gear issue and it appears all the gears work on my D17.  I have not loaded it down hill though.  Just held in the brakes and let out the clutch to see if it held.  Not sure that is a good test method so will have to wait to try it on a hill with a wagon.  Brakes seem good and overall I am happy with it.  If I can get the hydraulics working I will be very happy.   I am not real familiar with this site and perhaps can learn how to send a photo.   

Roger that.  I will give it a try.

The lift arms are not two-way cylinders. The require weight on the arms to gravity themselves downward when the Lift/Lower lever is held clear forward. Engine running makes lowering more difficult as there is a certain amount of back pressure in the system and that is normal. You can spray lube on the front of the spool while the spool is clear exposed. You can remove the aluminum cap with the hand lever in hold and blow all the rust and dirt off the spring and reassemble and heavily lube with penetrating oil.

Modern Universal hydraulic/transmission oil is what you need. A-C or AGCO 821 or 821XL specs. Dipstick is to the left of the gearshift. Filter is under the battery. If you have a factory 3-point hitch, usually the hitch will go down with the engine off by its own weight. You might have an issue with the lift cylinders being stuck in the UP position if they have been there for many years !! Beware of that possibility. If your hitch is a snap-coupler, stand on the right lift arm while you reach for the lift/lower lever and hold it fully forward (or tie it forward with a tarp strap/wire).

I am very thankful for his knowledge.   Hoping I can get my D17 issue resolved and it is a process for sure.   Every step of advice has been helpful.

It appears this tractor has had an issue for some time with the hydraulic and operation of the lift arms as there is slight rust on one of the cylinders which i was able to remove with polishing compound.   I tried to put pressure on the arms with a heavy long bar with my entire weight and they do not budge.   

I am assuming I have to remove the cover on top of the valve block so I can get to it.  When I disconnect it at the front will I be able to pull the spool through the valve block out the back in.   I tried to remove the screw on the back of the cup and could not budge it.  However,  I need to use a wider and heaver screwdriver and that would maybe work.   I was going to disassemble the spring and clean it all out and reassemble it.  Perhaps I will not have to do that if I can pull it through and out the back.   thanks on the wording on the balls.    

thanks for all your help.  I think I will remove the structure which you reference and that I called a cover so I can easily access the pin and make sure the spool end is clean before I pull it out the back end.   Great idea on how to remove and disassemble the rear spring and cup to clean up everything.  I am curious where the balls are located that can fall out if the spool is a straight piece from front to back?   Just want to protect my balls.   Some humor is helpful at time.

still worried about the balls?   Where are they in relation to pulling out the spool?  I am confused where they are located if the spool goes from the front to back?  are there indents in the spool and that position the level as you noted earlier?

Grab hold of the spring and the orange tube ahead of the spring and pull the whole thing out not letting anything shift or move. Lay it all out on a towel so things don't roll away.

thanks,   I will be working on the D17 early next week hopefully and will make sure I check out the linkage very closely.   I hope you have a good weekend.