Erratic Hydraulics

   / Erratic Hydraulics #1  

TRH

New member
Joined
Oct 24, 2010
Messages
13
Location
Bainbridge Island, WA
Tractor
Ford 1900
I have a Ford 1900 tractor with a Ford 771 loader on the front. In the 6 weeks I've owned it I have thoroughly cleaned and then lubed the whole machine. I changed the engine oil and the hydraulic fluid, cleaned the hydraulic filter and changed the fuel and oil filters. I think that the fluid changes were way overdue. I've put about 40 hours on the engine, equally divided between the loader and the backhoe. Both use the same hydraulic fluid reservoir and pump.

My problem is that the loader bucket is erratic in when it works. Sometimes when I am tipping (dumping) the bucket and stop tipping to raise it, it will not continue to dump. If I either raise it more or lower it, it normally works. Similar problem with raising the bucket. Sometimes if I stop raising, dump, and try to continue to raise, it will not raise. It always will go down (gravity?), but not always tip downward. Eventually it will work on both the dump and lift modes. So far, when I raise the bucket to the max, the dump function has always started to work again. It appears that there are no leaks in any of the hoses or cylinders.

I've had no problems with the operation of the backhoe, other than operator errors.

Any ideas?

Tom
 
   / Erratic Hydraulics #2  
My thought would be before thinking hydraulic problem, make sure pins are not binding in bucket. Take them out clean and grease. Make sure holes are not all wore out also. I have seen cylinders bend because of siezed pins.
 
   / Erratic Hydraulics #3  
TRH, by any chance do you have these problems when the engine is below 1000 rpm?
 
   / Erratic Hydraulics #4  
I think if you install a hyd gage in the system, you will find your problem, just by doing some logical trouble shooting
 
   / Erratic Hydraulics #5  
Sounds similar to the problem I have with my bucket dumping. If I let it dump too fast, it will take a couple of seconds to continue moving once the load has emptied from the bucket. Determined that the pump is not keeping up with the cylinders. I think this is caused by the loader valve being to big and lets the oil move through the system faster than the pump can supply oil back to the opposite side of the cylinders.

I will either have to put flow control valves in the lines or go to a smaller loader valve gpm to correct it. This may not be your problem but it sounds similar.

Currently I have a 10gpm valve on a 4gpm pump and 3/8" lines.
 
   / Erratic Hydraulics #6  
If I let it dump too fast, it will take a couple of seconds to continue moving once the load has emptied from the bucket. Determined that the pump is not keeping up with the cylinders.
Thats right, gravity dumps flow faster than the pump flow can refill....creates temporary vacuum or air get sucked in.

I think this is caused by the loader valve being to big and lets the oil move through the system faster than the pump can supply oil back to the opposite side of the cylinders.
Size of loader valve is basically not your primary problem, it is a pumpflow vs gravity flow problem.....Try to speed up pump rpm (throttle) while dumping, and it will show less of this "slack"....You can also slow down dump cycle with a one way restriction, but then you lose the benefit of quick dump cycle....usually a regen function is used to cure this problem.....



Currently I have a 10gpm valve on a 4gpm pump and 3/8" lines.
3/8" is perfect size...
10gpm valve is a little over sized, and will make it hard to feather functions...it will take almost full lever movement to build enough pressure to lift loads, and almost no lever movement to lower gravity loads.....
 
   / Erratic Hydraulics #7  
Thats right, gravity dumps flow faster than the pump flow can refill....creates temporary vacuum or air get sucked in.

Size of loader valve is basically not your primary problem, it is a pumpflow vs gravity flow problem.....Try to speed up pump rpm (throttle) while dumping, and it will show less of this "slack"....You can also slow down dump cycle with a one way restriction, but then you lose the benefit of quick dump cycle....usually a regen function is used to cure this problem.....




3/8" is perfect size...
10gpm valve is a little over sized, and will make it hard to feather functions...it will take almost full lever movement to build enough pressure to lift loads, and almost no lever movement to lower gravity loads.....

Thanks, what you have said is pretty much what I have going on. I wasn't trying to hijack the thread just putting out another possibility to what might be going on with his system. I'm going to replace the loader valve with one that has regen to see if that cures the problem.
 
   / Erratic Hydraulics #8  
Deere uses a regen circuit for this same problem. There is usually a valve to bypass when not needed. You'll still have a short hesitation, but not nearly as bad as without the regen.
 
   / Erratic Hydraulics #9  
Thanks, what you have said is pretty much what I have going on. I wasn't trying to hijack the thread just putting out another possibility to what might be going on with his system. I'm going to replace the loader valve with one that has regen to see if that cures the problem.

With regen, it should dump about 50 % faster. It may be to fast for you. Just pull it back out of regen.
 
   / Erratic Hydraulics #10  
With regen, it should dump about 50 % faster. It may be to fast for you. Just pull it back out of regen.

It will dump pretty fast as it is but then just like TRH is saying, it takes a few seconds before I can continue with any dump movement. If I pull it back up a little then I get dump control again. I need someway to get the discharge oil from the cylinders routed into the pressure side of the cylinders during the dump cycle so it will fill the cylinder faster. I am hoping regen does that.
 
 
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