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Discussion Starter · #1 ·
I’m about to dive into the files but was hoping someone can point me in a specific direction. My new to me 644 doesn’t want to pick up more than a few pounds. I’ll first say that forward/reverse and mid lift work perfectly. Proper oil in hydro tank.

Today I tried to pick up my 54” dozer blade on a small pallet and my FEL struggled to lift it at Full throttle. When I curl the bucket with weight it just droops down. It feels like the spool is bypassing but that would mean both lift and tilt are.

I ordered a pressure gauge and short section of hose to test pressure at TCV port to start with.

Im hoping the relief just needs to be reset.

Thank you in advance.
 

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'68 - Case 155, '73 - 646a
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Ben Welcome, always nice to meet more LOADER OWNERS.. If you're not getting oil leaking all over its likely a relief valve issue. Having said that:
1. Is the Hydro system running 15w or 20w-40 MOTOR OIL?
2. Have the cylinder been rebuilt and we know that they are not leaking internally?

If I recall correctly the Case Hydraulic manuals seem to indicate that the relief valve in the TCV for the LIFT Circuit has an effect on the loader. IF you can not get he lift circuit pressure up by adjusting the loader valve, assuming you have checked the spring and the ball, etc. Then you might need to check and adjust the LIFT Circuit pressure on the TCV.

For the TCV I don't know if this helps I saw this in the Case 'Timely tips' manual
121863


I also sent you a Private message with previous posts on Loaders specifically. Nothing much in there about loader vales other than this repair:
 

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Well, I'm tending to agree with the above post,
On the control valve for the bucket there is a pressure relief on that valve. The good thing is, it's fairly easy to get at. Till you get your gauge, you could pull the relief screw out of it and pull both the spring and ball out of it. (Battery and tray likely in the way, easy to pull out)
Just remember how many turns out, so you can at least reset the relief to where it is. You might need a small magnet to reach in there to get the spring and ball out. Be very careful you don't loose either pieces.

If everything turns out fine, stick it back in by the same turns in, and I'd wait to connect a pressure gauge onto it. Whiles you're waiting, might as well get familiar with test procedures,

The below, is one of several manuals available for this,

The other thing,
you should read up on, LL21 check valve. It's more relative to pallet forks, but if you think of the curl function, curl is curl, regardless what you're trying to curl. With forks, the moment is further out, so you have weight on forks further away from the mast. First time I tried mine with forks, I went up with lever, and the curl,, went down and just about lost my load. So, say a load suspended at end of bucket,, not sure which way it'll go. I guess it depends on the weight,,,
121864
 

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Discussion Starter · #5 ·
Ben Welcome, always nice to meet more LOADER OWNERS.. If you're not getting oil leaking all over its likely a relief valve issue. Having said that:
1. Is the Hydro system running 15w or 20w-40 MOTOR OIL?
2. Have the cylinder been rebuilt and we know that they are not leaking internally?

If I recall correctly the Case Hydraulic manuals seem to indicate that the relief valve in the TCV for the LIFT Circuit has an effect on the loader. IF you can not get he lift circuit pressure up by adjusting the loader valve, assuming you have checked the spring and the ball, etc. Then you might need to check and adjust the LIFT Circuit pressure on the TCV.

For the TCV I don't know if this helps I saw this in the Case 'Timely tips' manual
View attachment 121863

I also sent you a Private message with previous posts on Loaders specifically. Nothing much in there about loader vales other than this repair:
Thank you.

1) I am certain this unit is running the correct oil. It came from a longtime member that knows his stuff. Regardless I will be changing it soon.
2) I don’t know the internal condition of the cylinders. When sitting in the garage for a few days with pressure on them the curl cylinder and left lift cylinder have a small puddle underneath them.

I am fairly certain this is a new problem. The PO was trying to lift things but limited with no ballast. I put 200lbs in a rear box so no problems there.
 

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Discussion Starter · #6 ·
Well, I'm tending to agree with the above post,
On the control valve for the bucket there is a pressure relief on that valve. The good thing is, it's fairly easy to get at. Till you get your gauge, you could pull the relief screw out of it and pull both the spring and ball out of it. (Battery and tray likely in the way, easy to pull out)
Just remember how many turns out, so you can at least reset the relief to where it is. You might need a small magnet to reach in there to get the spring and ball out. Be very careful you don't loose either pieces.

If everything turns out fine, stick it back in by the same turns in, and I'd wait to connect a pressure gauge onto it. Whiles you're waiting, might as well get familiar with test procedures,

The below, is one of several manuals available for this,

The other thing,
you should read up on, LL21 check valve. It's more relative to pallet forks, but if you think of the curl function, curl is curl, regardless what you're trying to curl. With forks, the moment is further out, so you have weight on forks further away from the mast. First time I tried mine with forks, I went up with lever, and the curl,, went down and just about lost my load. So, say a load suspended at end of bucket,, not sure which way it'll go. I guess it depends on the weight,,,
View attachment 121864
Thank you

As a matter of fact I was trying to lift with pallet forks. So that’s pretty standard without the check valve for the curl to drop instead with a load? That’s good to know to eliminate that from the equation.

Im gonna pull apart the relief on the loader valve. Can I test that with my PSI gauge same as testing the TCV?
I would assume the ball and spring need to be installed to do that.
 

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Well,
Perhaps we should start over again.

1- Loader lift, good or poor. (without using the curl function). You can even stick a chain off the back of the fork assembly, and use that to lift with. up and down function only, rate it good or bad? 200-300 ibs of weight.

2-Curl function with be poor with out the added check valve! Originally, without it, pallet forks are iffy to use! With check valve,, works like a dream! (I'm thinking this is more than likely your bigger problem) Dealers sell a full complete kit which is the way I went. Saves running around to get parts and fittings and hoses!

3- When testing for pressure, relief has to be in place, without it, you'll get a straight bypass and have no lift or curl,,

Testing at the TCV should work, but use only 1 function at a time. When using any lift function, you should expect to see about 1100 PSI on the gauge, that's what you want to see on either mid-lift, 3 point or using the bucket lever. Aim for the top end,, manual says, 1050 plus or minus 50,, I added the 50 into it!

Lastly, I should add,
If you're like me and like tight control levers, that bucket lever,
Has 2 little flat plates that connects lever to top of valve spools. If you do end up order a check valve, from a dealer, I'd encourage you to replace those 2 plates (Parts #7 & #8). Much nicer then having floppy control lever,,,
 

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Discussion Starter · #8 ·
Well,
Perhaps we should start over again.

1- Loader lift, good or poor. (without using the curl function). You can even stick a chain off the back of the fork assembly, and use that to lift with. up and down function only, rate it good or bad? 200-300 ibs of weight.

2-Curl function with be poor with out the added check valve! Originally, without it, pallet forks are iffy to use! With check valve,, works like a dream! (I'm thinking this is more than likely your bigger problem) Dealers sell a full complete kit which is the way I went. Saves running around to get parts and fittings and hoses!

3- When testing for pressure, relief has to be in place, without it, you'll get a straight bypass and have no lift or curl,,

Testing at the TCV should work, but use only 1 function at a time. When using any lift function, you should expect to see about 1100 PSI on the gauge, that's what you want to see on either mid-lift, 3 point or using the bucket lever. Aim for the top end,, manual says, 1050 plus or minus 50,, I added the 50 into it!

Lastly, I should add,
If you're like me and like tight control levers, that bucket lever,
Has 2 little flat plates that connects lever to top of valve spools. If you do end up order a check valve, from a dealer, I'd encourage you to replace those 2 plates (Parts #7 & #8). Much nicer then having floppy control lever,,,
Thank you Lionel.
Lift is poor. It won’t lift my 54” dozer blade. I’m hoping to have time tomorrow to hook up the gauge and test.
 

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Discussion Starter · #9 ·
A little progress and another question.

I completely tore Down and rebuild the loader valve circuit with new o rings. the unit looks great inside! I hooked up my pressure gauge and get 475 psi when using bucket controls and mid lift no matter how tight the relief is. Drive circuit stops at 1800 psi and no longer stalls the engine. i did notice some metal glimmers when draining hydraulic system.

I’ve been waiting on parts for the TCV as I plan to rebuild that. While waiting I thought I’d swap out they hydraulic pump with a known strong one I just Pulled out of another tractor.

Here is my question, I disconnected the hardline from pump to TCV and oil flows straight thru the pump and drained the hydraulic tank. Should the pump be holding fluid from getting past?

Thank you.
 

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'68 - Case 155, '73 - 646a
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Gear pump would NOT stop oil there is a path around the outside of the gears where they don't mesh. Any gap larger than about .001" will pass oil freely

The 475 PSI problem MY be in the TCV lift circuit relief setting. That setting interacts with the Loader setting. Read the foot note with the **..
122726
 

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Discussion Starter · #11 ·
Thank you everybody for the help. I’m writing this post for anybody that has this problem in the future.

After I rebuild the loader valve block I also replaced the hydraulic drive motor with no change and ended up tearing apart the TCV (which is what I was avoiding). The lift circuit relief spring was broke into about 8 pieces. It was a pain to take that TCV out but totally worth it in the end. I replaced all of the seals and a few fittings that leaked. I lifted my first load yesterday and super happy having the whole hydraulic system refreshed.

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