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Discussion Starter #1
I’ve had a 1969 400 with the 7400 loader for a couple years and recently pulled the loader valve apart to reseal it and the pressure relief valve on the inlet port came came out in pieces. The brass insert in the spool was unthreaded and sitting sideways.

It seemed apparent how it should go back together, I got my thread file out and cleaned up the brass insert so it would thread all the way down, inserted the orfice and spring (there was no shim at the bottom of the port) and put it back on the machine.

The loader operates extremely slow however it has full lifting capacity so it seems like the pressure relief is assembled wrong but I don’t see another way to assemble it. Does anyone have any info on these old valves? The JD parts manual seems to agree with my assembly but it’s not a very good drawing.

The backhoe works normally so I know the pump is fine.

 

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Welcome to GTT
Have you considered viewing the parts schematics on JD Parts on line? Do I have correct portion of valve you referred to in photo?
 

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Welcome to GTT
Have you considered viewing the parts schematics on JD Parts on line? Do I have correct portion of valve you referred to in photo?
I think you have the correct drawing TxJim.

Chilliwack, that is a flow control valve, not a relief valve. Later serial numbers only had a plug.
 

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Discussion Starter #4 (Edited)
Thanks, that is the drawing I was using. It seems the spool can only go in one way as the orfice plate seems to need to seat on a surface above the brass insert and the spring on top of that.

The only thing I see a little unusual is the orfice plate is dished so I reinstalled the way the wear marks indicated and there was no shim at the bottom of the bore. The second time around I tried a .030 shim as well with no change. I can’t see the direction of the dish should make this significant a difference to the function.

Flow control as opposed to pressure relief makes sense with the symptoms. I have full pressure eventually, just very little flow. If later models didn’t have this, can it be left out or modified to stay in the full flow position?

Thanks for the welcome by the way, I poured over everything 400 I could find on this site when I got the machine and really appreciated the info from TxJim and others to figure out the closed center system and find the additional filter. I’ve been lurking a couple years now so I don’t feel that new.
 

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Thanks, that is the drawing I was using. It seems the spool can only go in one way as the orfice plate seems to need to seat on a surface above the brass insert and the spring on top of that.

The only thing I see a little unusual is the orfice plate is dished so I reinstalled the way the wear marks indicated and there was no shim at the bottom of the bore. The second time around I tried a .030 shim as well with no change. I can’t see the direction of the dish should make this significant a difference to the function.

Flow control as opposed to pressure relief makes sense with the symptoms. I have full pressure eventually, just very little flow. If later models didn’t have this, can it be left out or modified to stay in the full flow position?

Thanks for the welcome by the way, I poured over everything 400 I could find on this site when I got the machine and really appreciated the info from TxJim and others to figure out the closed center system and find the additional filter. I’ve been lurking a couple years now so I don’t feel that new.
Cessna is still around, maybe they might have some further information.
 

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Discussion Starter #6
From what I could gather from the hydraulic places around here, Eaton took over Cessna hydraulic motors but the valve division is defunct.

I will pull the spool out on the weekend and get a look at the port locations to try to get a better idea of how the valve is supposed to work. Maybe it will either become more obvious or I will be able to run it without the spool.
 

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The "block" that has the flow control is P/N AU40989. The block with only a plug is P/N U15577
So there may be internal differences :dunno:
 

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From what I could gather from the hydraulic places around here, Eaton took over Cessna hydraulic motors but the valve division is defunct.

I will pull the spool out on the weekend and get a look at the port locations to try to get a better idea of how the valve is supposed to work. Maybe it will either become more obvious or I will be able to run it without the spool.
Well bummer. Good luck with the discovery learning technique. Sometimes just taking something apart and reassembling will fix it.
 

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Discussion Starter #9 (Edited)
Well, been cold and snowy for the past couple weeks here and not going to attempt to take the 15,000 sled down the snow covered driveway to the shop.



Sun came out today so dropped the valve assy far enough to get the flow limiter apart and see how it should work. What I see is the brass orifice inside the spool provides a path from the main supply to the valve stack supply passage.




More flow through the brass orifice would cause more pressure on the orifice until it blocks off the supply port. I know I took it apart the same way I assembled it but the brass orifice was laying loose and the threads damaged so I’m pretty sure the spool should’ve been in the other way round so pressure isn’t pushing against the open end of the threads. This would also increase the static compression of the spring from about 1/4” to 3/4”.




I assume this is to protect power steering supply while using the loader but I don’t drive this thing at any speed, and the newer block doesn’t have this so I put it back together without the pieces and the loader is back to full speed. I’ll keeps the parts around in case it causes issues in the summer heat when pressures are lower.

Thanks again to everyone who helped , realizing it was a flow limiter helped me figure it out and maybe someone else googling 400 slow loader will stumble across this.
 
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