843 Bucket Positioning Valve ?

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Sep 22, 2014
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Finally got some time to run the 843 that I have been working on. This thing is one heck of a strong running machine!
Here is what is happening though:
When I have a full bucket of dirt, 7/10 times it will try to dump the bucket when I lift the boom. It acts like it is too heavy for the tilt cylender. However, when it does lift correctly, it holds just fine. It does not do it all the time, but about 7 out of 10 times it will do this.
Is the bucket positioning valve the only place that the lift/tilt systems work together?
If so, what in this valve would be likely the cause of this?
My other thought was that maybe the tilt cylender was bypassing the piston seals and maybe that is why it only does it with a heavy load, but if I lift the front tires using the bucket tilt, it does not bleed down on its own. I would think that doing this would rule that out as the cause, as well as it holding a load sometimes.
Any suggestions on where to look?
 

Bobcatdan

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I don't think a bucket positioning vavle was even an option on 843. Even if it was, it was then and to this day always an option. Machines don't automatically have them. If you did, the bucket would always move in sync with the arms because the early ones it can not be turned off. I would look at the cylinder or a port relief on the vavle as the source of your problem.
 

antfarmer2

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I don't think a bucket positioning vavle was even an option on 843. Even if it was, it was then and to this day always an option. Machines don't automatically have them. If you did, the bucket would always move in sync with the arms because the early ones it can not be turned off. I would look at the cylinder or a port relief on the vavle as the source of your problem.
Could you be engauging you aux hydro on my 743 the right stick moves back and forth to do this
 

Tazza

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Could you be engauging you aux hydro on my 743 the right stick moves back and forth to do this
Try lifting the bucket empty, does it stay flat? if so, you have bucket positioning, if not your tilt pedal may be sticky making it so when you lift you actually tilt a little. I had a machine like this, it would always tilt a little when i lifted, fixed teh tight spot and it was fine.
 
OP
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Sep 22, 2014
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Try lifting the bucket empty, does it stay flat? if so, you have bucket positioning, if not your tilt pedal may be sticky making it so when you lift you actually tilt a little. I had a machine like this, it would always tilt a little when i lifted, fixed teh tight spot and it was fine.
Thanks Tazza. I do have the bucket positioning valve. Have looked at it. The bucket does stay level when lifting it empty. it is a little jerky when "auto-tilting", but it does stay level. When loaded, I cannot even force it to stay level by pressing the tilt pedal while lifting. This is how I came to the conclusion that it is either the bucket position valve, or tilt cylinder seals... Which would you suspect? If it is the valve, What part of it would cause this?
 

Tazza

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Thanks Tazza. I do have the bucket positioning valve. Have looked at it. The bucket does stay level when lifting it empty. it is a little jerky when "auto-tilting", but it does stay level. When loaded, I cannot even force it to stay level by pressing the tilt pedal while lifting. This is how I came to the conclusion that it is either the bucket position valve, or tilt cylinder seals... Which would you suspect? If it is the valve, What part of it would cause this?
I would suspect the ram seals first.
The way the valve works is when you lift, it moves a percentage of fluid going to the lift arms to the tilt ram. So you lift and say 5% of that fluid goes to the tilt ram to keep it level. I believe the internals of the valve would be very simple using one way valves and adjustable orifices.
 
OP
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Sep 22, 2014
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I would suspect the ram seals first.
The way the valve works is when you lift, it moves a percentage of fluid going to the lift arms to the tilt ram. So you lift and say 5% of that fluid goes to the tilt ram to keep it level. I believe the internals of the valve would be very simple using one way valves and adjustable orifices.
Well I replaced the Tilt Cylinder (was going to rebuild, but rod was bent due to the lack of bucket tilt stops) and now have built some stops to keep from bending it again. The bucket still will randomly drop away (not a free fall, but faster than usual) when lifting the lift arms. If I run the arms all the way down and bottom them out, it will then act normal( as a bucket should with a bucket position valve), but will then soon return to dropping the bucket when lifting, and will not allow you to tilt back up without setting the bucket down on its cutting edge, driving back while tilting back and lowering the arms. once it begins to do this, if I just try to tilt back, it will try to raise or lower the lift arms unpredictably while still tilting the bucket... This leads me to believe that the problem lies in the bucket position valve. Thoughts?
 

Tazza

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Well I replaced the Tilt Cylinder (was going to rebuild, but rod was bent due to the lack of bucket tilt stops) and now have built some stops to keep from bending it again. The bucket still will randomly drop away (not a free fall, but faster than usual) when lifting the lift arms. If I run the arms all the way down and bottom them out, it will then act normal( as a bucket should with a bucket position valve), but will then soon return to dropping the bucket when lifting, and will not allow you to tilt back up without setting the bucket down on its cutting edge, driving back while tilting back and lowering the arms. once it begins to do this, if I just try to tilt back, it will try to raise or lower the lift arms unpredictably while still tilting the bucket... This leads me to believe that the problem lies in the bucket position valve. Thoughts?
From that description i think you are right that the positioning valve is at fault.
Can you pull it out and replace any Orings inside it? I don't believe they are that complicated, just different sized restictors and one way valves.
 
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