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641 won't lift, blows relief valve

O

Overland

New User
Hello, I'm hoping someone can shed a little light here for me. I have a 641 which won't lift at all.

Pump is rebuilt, bled, pours a steady stream from the bleeder back to the sump when bled.

Unloading control has been checked, cleaned, resealed, and continues to move freely.

Check valve has been checked and cleaned, back pressure valve appears to move and seat properly.

Lift cover adjustments have been performed by the book, everything appears to be in spec.

So here's what has me stumped: I can manually unload the unloader, start the engine, and hold it with the touch control raised. Once I let off of the unloader, the pump loads and the relief valve in the bottom of the sump sounds. Much turbulence in the sump, but the arms never move. I can drop the touch control, turbulence goes away. The unloader is unloading, the control valve is adjusted to spec, but doesn't seem to be porting the fluid in the right direction.

I have yet to check fluid pressure at the side of the case.

Does this sound familiar to anyone?
 
(quoted from post at 15:08:17 05/29/15) Hello, I'm hoping someone can shed a little light here for me. I have a 641 which won't lift at all.

Pump is rebuilt, bled, pours a steady stream from the bleeder back to the sump when bled.

Unloading control has been checked, cleaned, resealed, and continues to move freely.

Check valve has been checked and cleaned, back pressure valve appears to move and seat properly.

Lift cover adjustments have been performed by the book, everything appears to be in spec.

So here's what has me stumped: I can manually unload the unloader, start the engine, and hold it with the touch control raised. Once I let off of the unloader, the pump loads and the relief valve in the bottom of the sump sounds. Much turbulence in the sump, but the arms never move. I can drop the touch control, turbulence goes away. The unloader is unloading, the control valve is adjusted to spec, but doesn't seem to be porting the fluid in the right direction.

I have yet to check fluid pressure at the side of the case.

Does this sound familiar to anyone?
Click to expand...
ure looks to me like fluid can't get past the check valve.
 

Flow is reaching the unloading control, but no oil is coming down from the top. The cylinder safety valve appears to remain seated.
 
unload valve passage is plugged... or one of the passages for the fluid...check for blockage???? swag.
 

I put air to all of the holes in the cylinder on the bench, only one pushed the piston up. Control valve position made no difference, perhaps a return passage?
 
(quoted from post at 16:25:07 05/29/15)
Flow is reaching the unloading control, but no oil is coming down from the top. The cylinder safety valve appears to remain seated.
Click to expand...
don't know what you mean or the significance of the statement, " but no oil is coming down from the top."? When unloader moves to position that it needs to be in for LIFT, then it blocks the pump flow that previously was dumped back to sump via backpressure & unloader passages and the only remaining place for it to go is past the check valve & into the ram lift cylinder. As I said, it does not look like it can get thru the check valve. Are you sure the check valve and backpressure components were re-assembled correctly?
 
(quoted from post at 13:42:41 05/29/15)
(quoted from post at 16:25:07 05/29/15)
Flow is reaching the unloading control, but no oil is coming down from the top. The cylinder safety valve appears to remain seated.
Click to expand...
don't know what you mean or the significance of the statement, " but no oil is coming down from the top."? When unloader moves to position that it needs to be in for LIFT, then it blocks the pump flow that previously was dumped back to sump via backpressure & unloader passages and the only remaining place for it to go is past the check valve & into the ram lift cylinder. As I said, it does not look like it can get thru the check valve. Are you sure the check valve and backpressure components were re-assembled correctly?
Click to expand...

Sorry, read as relief valve for some reason. As not reaching the lift cover. Coming from the top would be in reference to the vented oil returning to the sump, cylinder safety valve, blown o-ring, or from the bore of the cylinder.

Far as I know, the check valve only goes in one way. Seat was clean. I don't recall seeing a ceramic ball in there before, but that's what it had. Looked ugly, but was smooth. Perhaps I could back off on the retaining plug so as to relieve spring pressure, and see if it lifts then?

I did not remove the back pressure valve bushing, only blew through with air. Goes one way, seats the other.
 
(quoted from post at 17:02:08 05/29/15)
(quoted from post at 13:42:41 05/29/15)
(quoted from post at 16:25:07 05/29/15)
Flow is reaching the unloading control, but no oil is coming down from the top. The cylinder safety valve appears to remain seated.
Click to expand...
don't know what you mean or the significance of the statement, " but no oil is coming down from the top."? When unloader moves to position that it needs to be in for LIFT, then it blocks the pump flow that previously was dumped back to sump via backpressure & unloader passages and the only remaining place for it to go is past the check valve & into the ram lift cylinder. As I said, it does not look like it can get thru the check valve. Are you sure the check valve and backpressure components were re-assembled correctly?
Click to expand...
Perhaps I could back off on the retaining plug so as to relieve spring pressure, and see if it lifts then?" Worth a try.


Sorry, read as relief valve for some reason. As not reaching the lift cover. Coming from the top would be in reference to the vented oil returning to the sump, cylinder safety valve, blown o-ring, or from the bore of the cylinder.

Far as I know, the check valve only goes in one way. Seat was clean. I don't recall seeing a ceramic ball in there before, but that's what it had. Looked ugly, but was smooth. Perhaps I could back off on the retaining plug so as to relieve spring pressure, and see if it lifts then?

I did not remove the back pressure valve bushing, only blew through with air. Goes one way, seats the other.
Click to expand...
Perhaps I could back off on the retaining plug so as to relieve spring pressure, and see if it lifts then?" Worth a try.
 

Okay, so if it lifts, what does that say about the check valve?

This began as a problem with losing prime, which turned to no lift. After it was R&Rd a few times, I was asked to look at it. Far as I know, the check valve maintains pump prime, and the back pressure valve maintains static pressure against the unloader.

By all means, correct me if I'm wrong.
 
(quoted from post at 17:17:53 05/29/15)
Okay, so if it lifts, what does that say about the check valve?

This began as a problem with losing prime, which turned to no lift. After it was R&Rd a few times, I was asked to look at it. Far as I know, the check valve maintains pump prime, and the back pressure valve maintains static pressure against the unloader.

By all means, correct me if I'm wrong.
Click to expand...
isagree on check valve maintaining pump prime. 'What say about check valve?" I would say either check is requiring too high a pressure to open or the pump is not supplying enough pressure to open it. The latter being unlikely as you earlier said that pump can be made to open the pump over pressure relief valve.
 
The check valve does not hold prime.
It is a one way valve that holds pressure in the cylinder to keep the oil from running out of the cylinder when the unload valve is in the neutral position.
I do not think your check valve is bad. It is made to open at about 100 psi and the relief valve is made to open at 2000 psi. Your check valve would have to really be stuck for it to hold over 2000 psi.

What I do not understand is when you said......
I can manually unload the unloader, start the engine, and hold it with the touch control raised. Once I let off of the unloader, the pump loads and the relief valve in the bottom of the sump sounds.

Can you explain this better.
For one the unloading valve is hydraulically positioned. That is what the back pressure valve is for.
How are you manually holding the unloading valve?

What I am thinking on my limit view of your problem.
The pump is full flow so it pumps oil all the time.
When the unloading valve is in the neutral position it just dumps the pumped oil back into the sump.
Either your back pressure valve is bad or you have problems in the unloading valve.
When you try to raise the 3 point with the control lever the unloading valve is really going to neutral and dumping the oil. When you let off of the control lever it is allowing the unloading valve to block off the dump port; building pressure in the system and causing the relief valve to blow.

a192544.jpg


a192545.jpg
 
(quoted from post at 11:03:47 05/31/15) The check valve does not hold prime.
It is a one way valve that holds pressure in the cylinder to keep the oil from running out of the cylinder when the unload valve is in the neutral position.
I do not think your check valve is bad. It is made to open at about 100 psi and the relief valve is made to open at 2000 psi. Your check valve would have to really be stuck for it to hold over 2000 psi.

What I do not understand is when you said......
I can manually unload the unloader, start the engine, and hold it with the touch control raised. Once I let off of the unloader, the pump loads and the relief valve in the bottom of the sump sounds.

Can you explain this better.
For one the unloading valve is hydraulically positioned. That is what the back pressure valve is for.
How are you manually holding the unloading valve?

What I am thinking on my limit view of your problem.
The pump is full flow so it pumps oil all the time.
When the unloading valve is in the neutral position it just dumps the pumped oil back into the sump.
Either your back pressure valve is bad or you have problems in the unloading valve.
When you try to raise the 3 point with the control lever the unloading valve is really going to neutral and dumping the oil. When you let off of the control lever it is allowing the unloading valve to block off the dump port; building pressure in the system and causing the relief valve to blow.

<img src="http://photos.yesterdaystractors.com/gallery/uptest/a192544.jpg">

<img src="http://photos.yesterdaystractors.com/gallery/uptest/a192545.jpg">
Click to expand...
i, John. Since he hasn't returned since Friday, we might as well discuss this among our selves. :) You say, "When you let off of the control lever it is allowing the unloading valve to block off the dump port; building pressure in the system and causing the relief valve to blow. " In this scenario, with unloading the dump port, why would the ram not lift the arms?
 
JMOR
I see your point.
The check valve has pump pressure all the time. The only reason it closes and does not send oil to the cylinder is because it is dumping past the unload valve.

If the back pressure valve was stuck
If the unload valve was stuck
If the control valve was stuck
in any position to make the relief valve blow
the check valve should open and the 3 point raise.
You may not be able to stop the 3 point from raising if any of the above were stuck but it should go up.

So what would build pressure and the 3 point not go up.
The check valve is stuck;
or the passage between the check valve and cylinder is clogged
or the piston in the cylinder is jammed and what he thinks is the relief valve blowing is really the safety valve blowing.
Note...
I do not know if the relief valve or the safety valve will blow first but if the piston is jammed it could blow one of them.
 
My notes show pump over pressure valve = 1950-2050# and ram safety valve = 2700#.
I had not considered the ram stuck, but I do believe that should be considered as a possibility. He has had the check valve apart and if he installed the part with a "T" cross-section backwards where the larger portion is against spring instead of smaller portion inside the spring, this would very substantially raise the opening pressure to where it might not ever open. It should be easy enough to determine whether check is opening or not & thereby whether ram is stuck or not by opening the accessory plate test port and operating the system. No flow=check not opening. Flow= check opening & ram stuck. What think?
 
I'm not dead, just smells like it.

The valve in the bottom of the sump is blowing, which I believe is a lower pressure than the cylinder safety valve.

The piston has been resealed and moves in the cylinder easily. Well, as easily as the packing allows.

I was manipulating the unloading valve with a bent piece of wire. I need to look a bit closer at the diagrams to see exactly what I was doing, but from the control valve side of the cylinder with my hand through the shift cover, I could hold the valve at the bottom of its travel and observe no noise or turbulence. Releasing the valve (with the touch control up) would allow it to move back, which would load the engine a moment and blow the valve in the sump. The turbulence I assume coming from the valve under the oil.

I appreciate the time y'all spend replying to this topic. I have a lot going on, but I won't forget about this.

Also, I'm an idiot. Somehow I thought putting air across the valve would make a difference with an unloading valve in between.
 
(quoted from post at 10:56:12 06/01/15) I'm not dead, just smells like it.

The valve in the bottom of the sump is blowing, which I believe is a lower pressure than the cylinder safety valve.

The piston has been resealed and moves in the cylinder easily. Well, as easily as the packing allows.

I was manipulating the unloading valve with a bent piece of wire. I need to look a bit closer at the diagrams to see exactly what I was doing, but from the control valve side of the cylinder with my hand through the shift cover, I could hold the valve at the bottom of its travel and observe no noise or turbulence. Releasing the valve (with the touch control up) would allow it to move back, which would load the engine a moment and blow the valve in the sump. The turbulence I assume coming from the valve under the oil.

I appreciate the time y'all spend replying to this topic. I have a lot going on, but I won't forget about this.

Also, I'm an idiot. Somehow I thought putting air across the valve would make a difference with an unloading valve in between.
Click to expand...
nteresting. I will be waiting for your observations at the test plug on the accessory cover.
 
We're pulling 1500 from the pump head, but nothing at the accessory plate. Referring to previous posts, this is somewhat low.
 
(quoted from post at 14:29:01 06/01/15) We're pulling 1500 from the pump head, but nothing at the accessory plate. Referring to previous posts, this is somewhat low.
Click to expand...
hen you push the unloader valve in with the wire probe, you push it to the unload position. Then upon commanding lift, it jumps back to the position for lifting (blocks unload flow) and the next thing that should happen is that the check valve should open, allowing flow to ram (past the test port on accessory plate). No flow at test port & popping of pump relief valve says to me that check valve is not opening. " He has had the check valve apart and if he installed the part with a "T" cross-section backwards where the larger portion is against spring instead of smaller portion inside the spring, this would very substantially raise the opening pressure to where it might not ever open. It should be easy enough to determine whether check is opening or not & thereby whether ram is stuck or not by opening the accessory plate test port and operating the system. No flow=check not opening."
I would recommend verifying that those parts surrounding/part of check valve assembly be re-examined.
Specifically the "T" cross-section part that is partially inside the spring in this picture (to immediate left of ball).
 
OK lets see if I can explain this with pictures.
Look at the first picture. (Lift Neutral)
You will notice the unload valve is pushed forward.
The oil comes out the pump pass the relief valve up to the check and back pressure valve.
The back pressure valve will open at lower pressure than the check valve will so the back pressure valve opens.
The oil goes down to the unload valve that is pushed forward so the oil port is on the small bore of the valve. The oil makes a U turn and goes back into the sump.
The lift does not go up or down.
This happens when ever the tractor is running.

a192714.jpg



OK now we want the 3 point to go up (Lift Up)
Look at Second picture
Notice the unload valve is push back.
The oil comes out the pump pass the relief valve up to the check and back pressure valve.
The back pressure valve will open at lower pressure than the check valve will so the back pressure valve opens.
The oil goes down to the unload valve that is pushed back with the large bore blocking the U turn port.
The system starts to build pressure to 115 lbs and the check valve opens sending oil to the lift cylinder piston.

a192716.jpg


Now if your check valve does not open like JMOR is suggesting the system keeps building pressure till the relief valve opens down in the sump to keep the system from blowing apart.
 
Today, I'll have a look at the check valve. Seems pretty unlikely that I would have installed anything backwards, but anything is possible. Will also take a shot at the back pressure valve while I have it apart. The manual mentions a tool, which I figure can be subbed with a bolt, nut, and washer.

Thanks for your time and interest. Will return with results.
 
(quoted from post at 08:38:37 06/04/15) Today, I'll have a look at the check valve. Seems pretty unlikely that I would have installed anything backwards, but anything is possible. Will also take a shot at the back pressure valve while I have it apart. The manual mentions a tool, which I figure can be subbed with a bolt, nut, and washer.

Thanks for your time and interest. Will return with results.
Click to expand...
hat part that you are thinking about pulling has been known to stick from corrosion to the point that applying too much pulling force will break the threaded end off. Caution is advised.
 
The exact part described was indeed assembled backwards. Once the spring was installed correctly, it just about threw the arms right off of it. I bled the pump for a good minute or so, then bled the test port as well. Seems to be perfect.

The real test comes in the morning, lift or no lift?
 
(quoted from post at 16:47:01 06/04/15) The exact part described was indeed assembled backwards. Once the spring was installed correctly, it just about threw the arms right off of it. I bled the pump for a good minute or so, then bled the test port as well. Seems to be perfect.

The real test comes in the morning, lift or no lift?
Click to expand...
xcellent! Sometimes the bear gets me, but sometimes I get the bear! :wink:
 
(quoted from post at 08:51:31 06/06/15) It's good. Thanks again, y'all.
Click to expand...
ou are more than welcome! I enjoy the interesting problems & especially when the other guy is willing to follow thru on the trouble shooting advice/tips, as you did. Remotely, no one can find the problem alone. As just one instead of two, it is just a guessing game.
 
JMOR, im having a similar problem with my 1956 600 series, i pulled the test port and no fluid...so it seems the check valve is not opening? i can pull the 3x5 adapter plate and there seems to be a good strong flow out of the pressure port. any suggestions or were to check next?
i put all new o-rings in, including lift piston and unloader valve

lift not doing anything...
 
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