Hydraulic Problem on X748 with Snowblower

   / Hydraulic Problem on X748 with Snowblower #1  

captplaid

Bronze Member
Joined
Dec 12, 2010
Messages
60
Tractor
John DeereX748
There's a weight box on the back. This problem was there last year, but not as bad. This year with weight in the box, it''s more pronounced.

If I turn the spout to the left on the snowblower, the 3pt weight box goes down. If I turn the spout right, the weight box goes up. If I turn the spout to the left all the way and feather the lever slowly to turn the spout right, the 3pt goes up first then the spout starts to swing, almost like a master/slave hydraulic condition.

Ok the obvious answer is "lift the 3pt and close the manual valve on the side of the SCV. Great idea. That's what the valve is for, but the 3pt still drops when the spout is turned left. Closing the valve doesn't help.

Now, If I lift the 3pt half way up and close the manual valve, the 3pt still goes down when turning the snowblower left. When I turn the snowblower right, the 3pt only goes up half way and stops where it was when I closed the manual valve.

First guess was the manual valve on the side of the SCV was bad. Nope. valve is good.

One of the next theories was the hydraulic cylinder for the 3pt or mower deck has a blow internal seal and is just pushing oil back and forth around the piston. I don't think the is the problem, but it is a suggestion.

Another theory is when I turn the spout left, the 3pt uses gravity and closes the cylinder. This creats something of a vacuum on the back side of the cylinder. When I turn right, oil closes the cylinder. When the cylinder piston reaches the hydraulic oil on the backside, the cylinder stops. So, with the manual valve closed to the cylinder, it's acting like a oneway hydraulic cylinder and power up only.

That little manual valve on the SCV is on the line it is supposed to be. There would be a lot adapting to make it fit on the other line

Anyone have a better guess what is going on here.

While I havent compared the two, a friend has a 435 with a 3pt with a weight bar and blade on the front. He does not have this problem.

Thanks
 
   / Hydraulic Problem on X748 with Snowblower #2  
John Deere Parts lookup (you can do this also) shows an optional flow control valve that shuts off lift cylinder pressure to keep the rear lift stationary. Either you have it or you don't. If you do, find it (its right near the valve control block) and close it. If not, you need to add a AM134625 FLOW CONTROL HYD. VALVE between the valve block and the lift cylinder.

That's all folks !
 
   / Hydraulic Problem on X748 with Snowblower #3  
Have you tried adjusting the depth control rod on the 3PH to not allow movement of the 3PH lift arms?
 
   / Hydraulic Problem on X748 with Snowblower
  • Thread Starter
#4  
John Deere Parts lookup (you can do this also) shows an optional flow control valve that shuts off lift cylinder pressure to keep the rear lift stationary. Either you have it or you don't. If you do, find it (its right near the valve control block) and close it. If not, you need to add a AM134625 FLOW CONTROL HYD. VALVE between the valve block and the lift cylinder.

That's all folks !

Yeah, when I talk about a manual valve, that's what I mean. It's #18 to replace #13. It's there instead of the elbow. Expensive little sucker! It is working and not stripped.

MP37738________UN17MAR06.gif
 
   / Hydraulic Problem on X748 with Snowblower
  • Thread Starter
#5  
So when I swing the spout left, it lets oil out of the mower lift cylinder, extends, and lets the 3pt or deck down.


If I did not have the weight box on the back, I wouldn't have this problem. Unless there is a problem in the hydraulic control valve, it looks to me this is how it is supposed to work.

Do I need to put another inline flow valve on the other line to shut off oil to both sides of the cylinder? I realize JD doesn't make sell such a valve for this application, the the line can be cut and something installed inline.

Am I the only one who has this problem?
 
   / Hydraulic Problem on X748 with Snowblower
  • Thread Starter
#6  
Could there be something wrong in the SCV causing this?

MP26883________UN25JAN02.gif
 
   / Hydraulic Problem on X748 with Snowblower
  • Thread Starter
#9  
Dang. I'm surprised they had the same discussion today.

Thanks.

www.Aux-Hyd.com
 
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   / Hydraulic Problem on X748 with Snowblower #10  
Just an FYI on that aux-hyd valve. I put that on my old x485 and also had the issue of the 3PH moving with one of the FEL circuits - can't recall which function. Good luck.
 
 
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