Help Troubleshooting 3 point lift

[jenkinsph]

I am in the dark without any drawings to look at. I have to ask a few questions to get a better idea of what is happening.
Is the engine loading down when you attempt to raise the hitch? Do the hydraulics squeal or hiss excessively?
If not it would indicate the piston seals on the rockshaft may be shot and fluid is passing around the piston. When you let off the control lever the piston would still hold its position if there are no leaks in the lines or external leaks on the rod seals.
If the engine does load down and you have already determined you have 1500-2500 psi pump pressure you may have restrictions in the flow path between the valve and the rockshaft cylinder. Since you did not mention any loading or squealing I tend to think this is not the problem.

Since you have pressure to the remotes in the correct pressure range I doubt the pressure relief is the problem. Usually you would have only one relief valve for the entire system at the end of the flow path and that would protect the upstream remote valve(s) and the rockshaft valve. When testing the remote with a pressure gauge at the 2500 psi you should be able to detect flow through the relief line returning to tank. I use a long screwdriver if needed and hold it on the line and put my ear to it to listen, may have to have a helper operate the remote lever for you.

A screwdriver or cheap stethoscope can be used to check other lines if these are exposed too. It would be good if you can check for flows through the rockshaft valve and the rockshaft cylinder lines too.

So far I am betting on the rock shaft cylinder piston seals are the problem.

 

[ovrszd]

Correct me if wrong, I think each valve body also has a relief valve. Otherwise how would the system protect the pump when you try to lift a load heavier than the FEL is capable of. When I'm holding the lever in the "lift" position the center of the valve is closed and all of the pump flow is directed to said cylinder. If there's no movement or limited movement doesn't a relief valve open to allow continuous pump flow? Otherwise the pump would be deadheading?

 

[jraffini]

I am in the dark without any drawings to look at. I have to ask a few questions to get a better idea of what is happening.
Is the engine loading down when you attempt to raise the hitch? Do the hydraulics squeal or hiss excessively?
If not it would indicate the piston seals on the rockshaft may be shot and fluid is passing around the piston. When you let off the control lever the piston would still hold its position if there are no leaks in the lines or external leaks on the rod seals.
If the engine does load down and you have already determined you have 1500-2500 psi pump pressure you may have restrictions in the flow path between the valve and the rockshaft cylinder. Since you did not mention any loading or squealing I tend to think this is not the problem.

Since you have pressure to the remotes in the correct pressure range I doubt the pressure relief is the problem. Usually you would have only one relief valve for the entire system at the end of the flow path and that would protect the upstream remote valve(s) and the rockshaft valve. When testing the remote with a pressure gauge at the 2500 psi you should be able to detect flow through the relief line returning to tank. I use a long screwdriver if needed and hold it on the line and put my ear to it to listen, may have to have a helper operate the remote lever for you.

A screwdriver or cheap stethoscope can be used to check other lines if these are exposed too. It would be good if you can check for flows through the rockshaft valve and the rockshaft cylinder lines too.

So far I am betting on the rock shaft cylinder piston seals are the problem.

I'm not getting any load down with the 3 point. It loaded down when I tested with the remote port, but not with the 3 point. I've tried just simply raising without any load and leaving it up, then trying to get it to go down, and it seems to want to stay in place. I was thinking that might mean the seals are good, but obviously I'm only putting about 250lbs on it by standing on the lifter arms. If I'm understanding you, you're saying if the engine isn't loading down when I try to raise it, then it's probably not getting resistance trying to lift it, which would indicate a bad seal on the piston? That makes sense to me for sure. Thanks!

 

[jraffini]

Correct me if wrong, I think each valve body also has a relief valve. Otherwise how would the system protect the pump when you try to lift a load heavier than the FEL is capable of. When I'm holding the lever in the "lift" position the center of the valve is closed and all of the pump flow is directed to said cylinder. If there's no movement or limited movement doesn't a relief valve open to allow continuous pump flow? Otherwise the pump would be deadheading?

The FEL on my machine has its own pump and valve body that are totally independent of the 3 point and remote hydraulics. I believe there's only one relief valve as it pertains to the 3 point and the remotes, but I could definitely be wrong. I'm super new to hydraulics. Just trying to save a few bucks with a cheaper machine haha. Thanks!!

 

[ovrszd]

The FEL on my machine has its own pump and valve body that are totally independent of the 3 point and remote hydraulics. I believe there's only one relief valve as it pertains to the 3 point and the remotes, but I could definitely be wrong. I'm super new to hydraulics. Just trying to save a few bucks with a cheaper machine haha. Thanks!!

Oh yes, sorry, I forgot you mentioned that earlier....

 

[jenkinsph]

I'm not getting any load down with the 3 point. It loaded down when I tested with the remote port, but not with the 3 point. I've tried just simply raising without any load and leaving it up, then trying to get it to go down, and it seems to want to stay in place. I was thinking that might mean the seals are good, but obviously I'm only putting about 250lbs on it by standing on the lifter arms. If I'm understanding you, you're saying if the engine isn't loading down when I try to raise it, then it's probably not getting resistance trying to lift it, which would indicate a bad seal on the piston? That makes sense to me for sure. Thanks!

Correct ^^^


Before I took this apart I would see if I could verify flow to the rockshaft cylinder. If this can be verified without a lot of trouble I would do it. Is your rockshaft valve external on your tractor? Some are and some are internal, if it is internal you would probably have to take the top off for either repair.

Not having seen this tractor makes diagnosing more difficult and there is the question of position control too. On a Deere 4520 such as I have, you have to have the feedback shaft working in order to control the plunger/spool to get lift. I think this can be eliminated if your hitch will rise from the low to highest position on its own (even if very slow to do it).

On another note if you had water in the system this may have frozen and split the fel cylinders. If the cylinder split on the lower side I think this is a good guess.

 

[jraffini]

Correct ^^^


Before I took this apart I would see if I could verify flow to the rockshaft cylinder. If this can be verified without a lot of trouble I would do it. Is your rockshaft valve external on your tractor? Some are and some are internal, if it is internal you would probably have to take the top off for either repair.

Not having seen this tractor makes diagnosing more difficult and there is the question of position control too. On a Deere 4520 such as I have, you have to have the feedback shaft working in order to control the plunger/spool to get lift. I think this can be eliminated if your hitch will rise from the low to highest position on its own (even if very slow to do it).

On another note if you had water in the system this may have frozen and split the fel cylinders. If the cylinder split on the lower side I think this is a good guess.

I can verify that I'm getting flow to the cylinder. My first step was to clean a spring that I understand is connected to the control valve. I had read that's a common issue. After cleaning that off, the next time I tried the lift I heard a pop and started getting oil coming from a seam on the front of the control area. I popped off the front section and found a blown out seal at the front of the cylinder. That fixed the leaking. It seems since I'm getting proper pressure readings at the remotes, and I'm getting flow to the cylinder, all signs would point to needing to replace the actual cylinder wall seal. Does that sound right? I know it's hard without having drawings of my particular model setup, but I think I'm tracking with you. I'm totally new to hydraulics. I've done plenty of mechanical stuff, and do well with systems, I've just never touched hydraulics before. Thanks so much for the help!!

 

[ovrszd]

The cylinder gland seals/O-rings would have to be in horrible condition or completely gone before the arms wouldn't lift against any resistance. Most common indication of bad cylinder leakage is that it won't maintain a height. For example, if the seals were sooooo bad that it won't lift faster than a snails pace and only with no load then they would be so bad that as soon as you stopped activating the lift mode they would settle back down.

My Ford's seals were so bad that the tractor constantly had to readjust and relift to maintain height. When you shut the tractor off even without load the arms would immediately start dropping. But it would still pick up and carry a brush cutter. I rebuilt the cylinder to take some of that stress off the system of having to constantly readjust height.

Your water and potential freezing and busting issue makes it hard to logically evaluate exactly where the problem is. We don't know what freeze breakage is involved here. Probably not going to know without pulling the 3pt system off the top of the rear end. Without pics it's kinda hard to know what that involves. Most tractors are relatively easy to remove. When you do that you will get the lever, valve and cylinder all in one piece.

 

[ovrszd]

I'm really having trouble finding any detailed drawings of the 3pt system. Also not finding any replacement parts yet. I did find this website and the page I linked has a drawing of the 3pt assembly that bolts to the top of the rear end. Looking closely at the drawing you can see that there are vertical bolts going down thru the assembly and fastening it to the rear axle assembly. This is the common method. That pictured unit will need to be removed from the tractor to investigate the control valve assembly and lift cylinder which are both on the underneath side. Sorry I can't find better details.

Hydraulic System Parts

 

[jraffini]

http://tractorpoint.com/pdf/Long-Service-Manual-360-460-510-series.pdf

I found this repair manual online for a long 460, which I understand to be the same tractor in most every way other than color. I've been using it as my reference. It's got the details on the hydraulics. I'll be tearing into the system either way, so it's sounding like pulling the whole unit off and trying to go through it might help identify the problem. The current status seems to be that it functions, but not under any kind of load. It is getting correct pressure to the control unit. The tractor doesn't load down when attempting to operate the lift. In going to look tonight, but I believe there is a access point on the top that allows viewing of the back side of the cylinder, so I would be able to get an idea of just how much oil is flowing past the seal. I'll report back shortly on how that looks. Thanks everybody!