Ford 641 Hydraulics issue

TheCarDoc

Member
I have a 59' 641 I am in the process of going through. Here is a little back story. My Dad purchased the tractor a couple of months ago for the incredible expense of $250. The tractor had been sitting at the very least 5 years. I built the motor in it and thats when we found that the hydraulics didnt even try to work. I had him get the seal kit for it and we pulled it down. The fluid had a whole lot of water in it. Completely white. We drained, Cleaned and refilled the sump. All seals have been replaced and the piston resealed. We found the one seal missing between the piston and top plate. After reinstalling and priming the system we started it up. Immediately the lift goes all the way up, regardless of lift position. I should also mention we replaced the cam dowel pin. It had worn flat. I removed the plat and disconnected the control valve rod and removed it to make sure it was not staying engaged. reinstalled top plate, same thing. I removed again and used air to check and make sure the unloading valve is free and the check ball. Everything is free. New seals. But If i put air in the supply on the plate it immediately kicks up the arms no matter what. I was already leaning towards it being the draft control damaged in some way but I am just looking for some confirmations and maybe some advice on what to try. I removed the spring and everything off the draft rod on the outside of the top plate. Its not bent or broken so im not sure. Any help would be greatly appreciated.
 
Does the control valve travel stop to stop with the three point control lever? If so maybe the "free unloading valve" is not so free!
 
The control valve moves freely. and the unloading valve does also. Ive pulled the plug on it twice. Checked the seal and changed the new seal to a newer one on the unloading valve just to check. When I apply air to the top plate the unloading valve moves and then the arms go up still regardless of lift control position. Its puzzling. I have worked on several of these and Im thrown for a loop.
 











Take the PTO shifter cover off and see what the control valve is doing when the lever is moved!













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Ive actually used a mirror through the inspection/fill plug on the top plate. You can move it fully in and out but no change in operation. Arms go up no matter what.
 
You say that no matter the position of control valve, that the unloader valve moves to the lift position whenever air pressure is applied, correct? That says, to me, that the control valve is not moving far enough OUT (toward rear). For lift to happen, the control valve is in position to direct the pressure to both sides of the activating part of the unloader, whereas to 'hold' or 'lower', the control valve should be OUT far enough to dump the larger side (front) of unloader activating piston to sump via the baffle plate opening.
 
Correct, regardless of control valve position the 3 point goes up. I actually removed the top plate and removed the control valve rod from the unit. And still the same. The control valve is bottom on the retainer plate in the fully released position. The control valve spring is very stiff but the unloading valve will still open to the front position and the arms start going up as soon as the engine is spun over.
 
(quoted from post at 12:44:51 04/05/17) Correct, regardless of control valve position the 3 point goes up. I actually removed the top plate and removed the control valve rod from the unit. And still the same. The control valve is bottom on the retainer plate in the fully released position. The control valve spring is very stiff but the unloading valve will still open to the front position and the arms start going up as soon as the engine is spun over.
on't understand this: "...unloading valve will still open to the front position..". Unloading valve moves toward REAR of tractor for Lift, thus closing the unload/bypass path & forcing flow to go into lift ram cylinder.
 
Maybe it is time to remove the control valve bushing and remove the debris "peace's of Teflon tape" from the passage ways. BTGT too
 
yes, the unloading valve stays in the front position. And lifts anyways. I should have clarified. I removed the unloading valve, inspected and reinstalled in the rear or open position. When i applied air, the unloading valve moves to the front position without the control valve rod connected but still, the lift arms raise. We pulled all of the valves and valve seats/bodies when we did the seals. Checked, cleaned and throughly blew the the passages to make sure no debris,was in the system. I am going to pull the top plate again tomorrow hopefully and i will try and get a video to post to show whats going on. Thanks so far guys.
 
Also, I am an idiot. My open and closed descriptions for the unloading valve has been reversed. Regardless of lever position theunloading valve is moving to the open position. Sorry guys. Its been a long two days with this bad weather.
 
OK, very muddied by terminology & subsequent reversal. Not sure what you mean by open/closed as to unloader. Movement forward and aft is always clear. If, by open, you mean that the two paths toward the right (rear of tractor/aft) in the drawing are connected as shown , thus allowing flow between the two, shown in green, then it should not lift. If all the above is true, then I suspect that the backpressure valve is stuck closed or assembled with wrong spring. If not true, please explain further.
 
Okay, they unloader valve, with pressure applied goes in forward position regardless position of the control valve and it lifts and will not let down. With the accessory plate off and applying air, the check ball moves freely but it requires almost double pressure to move the back pressure valve.
 
(quoted from post at 16:52:10 04/05/17) Okay, they unloader valve, with pressure applied goes in forward position regardless position of the control valve and it lifts and will not let down. With the accessory plate off and applying air, the check ball moves freely but it requires almost double pressure to move the back pressure valve.
believe that if you swap the two springs, you problem will be resolved. Stronger spring belongs on check. Weaker on BP.
 
You Sir, are my current hero. I did not even think about that. This is the typical occurance when too many hands work on something. I just swapped the springs and all is good. My Father and myself send our Thanks.
 
(quoted from post at 18:21:26 04/05/17) You Sir, are my current hero. I did not even think about that. This is the typical occurance when too many hands work on something. I just swapped the springs and all is good. My Father and myself send our Thanks.
ou are welcome. The most difficult part was communication. I enjoy interesting puzzles. These days, I leave most of the 'routine' stuff to others or the archives.
 
I understand. Im the same way. Theres no room for pride though. Theres always someone who knows more. And I am very appreciative. Hopefully this will help someone else one day.
 

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