640 lift issues still.

grandpa Love

Well-known Member
So ....we bought tractor,it had
been sitting out in weather for a
least a year. Lift worked 1st time
we tried it. But control lever was
so hard to move that we broke it
off. Well we thought that to
remove quadrant we had to pull
cover off. Only thing that fixed
was with it sitting in its side
penetrating oil worked it's way
down tube and lever works smooth
now. Put cover back on ( heavy
thing, ain't it) no lift. Back
off. New o rings. No lift. Rev
motor it lifts. Sits a few days
,no lift again. Got rubber tube
ran it from plug on pump to filler
hole. Had very little air in it
,still no lift. When I turn off
tractor the fluid doesn't stay at
top of plug hole, but if you bump
starter it comes right out. What
am I missing? Because the old
fluid was full of water ,milky
looking ,we shot some air in the
plug hole on pump to clear it out.
Re placed all o rings under the
plate under seat too. Plus the two
between cover and housing.
 
Adjusted this linkage until it almost came out of threads ,then tightened it up enough to stay together. Now lift works. But after it lifts and Its up for a few seconds there is a leak ,looks like from front of where piston is . Release valve? Or not good also arms don't want to go down without pushing on em. Won't lift at all unless you pull lever all the way up. Once it starts lifting you can adjust it to any height and it stays there. Even with a bush hog on it. Uggggggggggghgh
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Well not going down with out pushing on them is normal since there power up and gravity down and the arm do not weight enough to push them self's down. As for the leak your seeing sounds like you need new piston 0-ring and backing washer
 
Not likely to cause the other problem unless the arms fall then go back up again due to cylinder leak down. To really check the 3 point out you need something hanging in the arm to judge how it is or is not working. Even if all it is, is a draw bar with you standing on it to judge how it is working
 
Got a 4' bush hog on it. Works fine after it gets going. Seems to lose prime to easy .gotta rev motor to get lift going.
 
This quote came from ZANE, theres more on his post.-----------If it is determined that the pump is operating right and supplying enough volume of oil under pressure to the hydraulic system then you may have a sticking unloading valve in the lift ram cylinder housing.

If the lift is jumping/bumping/hiccupping it is caused by the lift trying to hold the height constant with a leak internally of the hydraulic system. The leak must be fixed before these symptoms will go away. Common leaking places are the ram cylinder O ring/s, the pressure relief valve, the O ring on the unloading valve or a blown gasket under the ram cylinder to housing flange surfaces.
On the 53 and up Ford tractors there is a gadget named the unloading valve. It is hydraulically shifted by the movement of the control valve. The control valve does not actually move oil to the ram cylinder. The oil is directed to the ram cylinder by the position of the unloading valve. The Hundred series has the same valve in a slightly different form but performs the same function.
If and when the unloading valve stops moving then the lift won't lift until the problem that is causing this condition is fixed.
A faulty back pressure valve can cause the unloading valve to stick.
The unloading valve can stick on it's own.
The unloading valve has an O ring that can become worn until it will not allow the valve to move.
The pump could have lost it's prime too. The piston pump must be bled by opening the front head plug in the pump and running the engine slowly until all air bubbles are gone from the escaping oil. Stop the engine, replace the plug and start the engine again to see if that fixes the problem. It can! -----------Someone also said to only use the Ford co. oring or youll be sorry you didnt.
 
I read ZANE's whole post. Nothing
jumped out at me. Lift works
perfectly ,after it starts
working. Seems to lose prime. Have
to rev up motor to get it lifting
,after that it works fine. No
drifting down. No hic cups. It has
a Bushhog attached to it and it's
no issue. Why does it lose prime.
? Fluid is not being lost in
transmission. We cycled lift 100
times at least and fluid never
dropped below lowest bolt holes in
PTO shifter plate. (which is off).
Keep in mind tractor had not been
started in a year when I got it,
lift moved instantly first time we
started it. A guy made me a great offer on this tractor and I want it right before I sell it to him. Thanks for any help
 
Is that as difficult to do as it
sounds? Read a few ( hundred)
posts and not sure I want to try
it. Did blowing all the watery
fluid out cause the issue?
 
Lets try to clear some of this stuff up.

Here is a picture of the lift system in neutral position.


a174259.jpg



Now you say you have a leak in the front of where the piston is.
So lets clear up to the left of the picture is front.
If you read enough post you will see a leak at the main piston is common.
So the fast not thinking answer is change the O-Ring on the piston.
But wait you said the "front"
If you will look at the picture good you can see there is suppose to be a leak to the front when the hyd control is in neutral. It also leaks here in the down position. This is where the constant pumping pump relieves it self.
So lets clarify where the leak is before we fly off and have you spend time and money fixing not broken parts.

Next you said the arms will not go down.
You also said you adjusted the control valve linkage all the way out.
So lets add a picture of down position.


a174262.jpg



Now the lift arms should go down with nothing on them if you have the lift cover adjusted right.
So lets look at what is different in neutral (first picture) and down (second picture)
Pay attention to where I put the 2 yellow dots.
If you notice; If you have the linkage adjusted to long by just a little you can not get the valve to move back far enough to open the 2 passages that allow the lift to go down.
You can stand on the arms; jump on them; or build a house on them.
If you do not have that linkage adjusted right you will raise the front of the tractor before you overcome the hyd pressure in the system.

So the first thing you need to do is properly adjust the control valve linkage.
This takes a special tool per the Ford service manual.
The FO20 manual tells you how to fudge it if you do not have the special tools.
If you do not have a FO20 manual let me know and I will dig it out and post the page.

Now that you have the control valve set lets look at up position.


a174265.jpg



You will notice that under hyd pressure the unload valve has moved back.
In your picture I see what looks like a leak right on the back side by the plate where the control valve meets the linkage.
The control valve is a machine fit so there is not much you can do except replace the whole valve.
BUT the control valve is just above it and it has a O-Ring on it.
This control valve O-Ring may be leaking.
Hard to tell from the picture.

I mention this because now that you have control valve set right you still have to find the original problem.
First I would be checking pressure from the pump to make sure it is working properly.
If so the next thing I would check is the O-Ring on this unload valve.
If this O-Ring is leaking badly it will not allow the pressure to build up to move the unload valve.
If the unload valve does not move under hyd pressure the lift is NOT going to go up.
 
Dang typing faster than thinking.


Lets change 1 paragraph.


You will notice that under hyd pressure the unload valve has moved back.
In your picture I see what looks like a leak right on the back side by the plate where the control valve meets the linkage.
The control valve is a machine fit so there is not much you can do except replace the whole valve.
BUT the [b:654c4848f0]unload[/b:654c4848f0] valve is just above it and it has a O-Ring on it.
This [b:654c4848f0]unload[/b:654c4848f0] valve O-Ring may be leaking.
Hard to tell from the picture.
 
Hey John, thanks for replying and the pictures. Very helpful. Also while reading your answer we took another look at pictures I took. My wife says that the " leak" towards front ( of tractor ) only started when lift was up all the way and holding. The small hole above where I adjusted linkage was oozing oil until something came out to end and stopped it ,she was able to see this better than I was. Oddly today in pouring, swirling rain,I walked out to the barn and crunk up tractor ,lift went up as soon as I moved lever. But.....last night I didn't move control lever all the way down ,left it half way up ,it held it's position just fine. Is it possible to go too far down? Also should fluid ever leak out of here? It was so I tightened it until it stopped 1st picture. 2nd picture is of leaks. 3rd is linkage ,is arrow pointing to the place you should measure? We have the FO-20 manual. Also the lift arms do go down fine, with a push, or very easy after we attached an implement. Sorta panicked on that.
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(quoted from post at 15:09:11 10/08/17) I read ZANE's whole post. Nothing
jumped out at me. Lift works
perfectly ,after it starts
working. Seems to lose prime. Have
to rev up motor to get it lifting
,after that it works fine. No
drifting down. No hic cups. It has
a Bushhog attached to it and it's
no issue. Why does it lose prime.
? Fluid is not being lost in
transmission. We cycled lift 100
times at least and fluid never
dropped below lowest bolt holes in
PTO shifter plate. (which is off).
Keep in mind tractor had not been
started in a year when I got it,
lift moved instantly first time we
started it. A guy made me a great offer on this tractor and I want it right before I sell it to him. Thanks for any help
---I have a tractor that will only lift if i rev the engine a little. works fine then. I think my unloading valve is sticking and the rev throws a little more pressure at it. Its on a loader so I dont use it that much but if i need it that little rev works every time.
 
First picture with yellow arrow; That looks like the pipe plug in the plate that covers where a hyd remote control will go.
It is a plug so it should not leak.

Second picture with yellow arrow; The yellow arrow is pointed to the back side of the unload valve.
There is a gasket behind that plate with the 2 bolts and the unload valve has a o-ring on it.
While I feel there should be no leaks here I am willing to admit I really do not know.
You would be better off asking that question to JMOR as it has been years since I have had that apart.

Third picture with blue circle; That is the control valve. To adjust position control you measure from the machined surface on the housing (red circle) to the back side of the control valve (red line)


a174293.jpg



Where it is suppose to leak is on the front side. This is where the system dumps. (red arrow)


a174297.jpg
 
Thanks again John. Where is JMOR? He usually answers these types of questions , lol. So thinking that " leak" on front is not issue. Because I have messed around with the adjustment I better go back and check that. Would be nice to have the Nuday tools! May hunt some down. Once this 640 is done I have to replace the cam follower pin on my 960. That lift has been having issues last few times a used it. Pin is on my desk ,just need time. Thanks again for your help on this. Maybe this rain will be out of here by morning and I can go work on it some more.
 
Any idea why the lift worked today,after I left arms part way up overnight? Can it be lowered too far?
 
Well I guess at this point I just wait and see if it continues to work properly. Went down to barn few minutes ago and it raised right up at idle. Fingers crossed! Lol. Possible it just needs working? Nothing good comes from sitting in a driveway for a year.
 

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