Go BottomRear Hitch with Blade Quits for No Apparent Reason
 | Loren Larkin
Join Date: Posts: 1 
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2003-01-25 48125
We have a 1996 B7100HSD (390 hours)with a back 3 point hitch attached to a 7 foot blade. The weight of the blade is within the acceptable limits for the tractor. I can back blade for awhile when all of a sudden the thing won't lift. If I go in the house and have a cup of coffee and wait about a half hour, the thing will lift and work fine for awhile and then quit again. I always hear a real short clang before it stops working. When I hear the clang, I know the blade won't lift anymore. There is no set amount of time before it stops working. It can be an hour or a few minutes. It seems to be when the blade is under a strong load but I'm not sure. It was suggested that we check the screen (located behind a bolt at the end of the steel hose where it meets a banjo fitting) for gunk which we will try but if that doesn't solve the problem, does anyone out here have any other ideas? The tractor was recently purchased and the back hitch has never been used. The fluids were all just changed and the hydraulic fluid is nice and clear and the levels are good. We have a front loader attatched which works perfectly. The tractor is kept in a heated garage. We tried Art's suggestion of messing with the adjusting bolt and while we got the lowering speed we wanted (it was dropping really fast)that hasn't helped the problem of it quitting. It's worth noting that this tractor has been babied since it's purchase in 1996 and very well maintained by the previous owner, he just never used the back hitch.
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| Skylark
Join Date: Posts: 1
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2003-01-25 48126
FYI, I am now registered as Skylark
Loren Larkin
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| TomG
Join Date: Feb 2002 Posts: 5406 Upper Ottawa Valley 
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2003-01-26 48180
Sorry I missed responding this morning.
Trouble shooting over the net can take awhile to zero in on a problem, and I don't know much about 7100's. I seem to recall that they don't have a position control 3ph but I might be wrong.
I'll start by asking if the loader works when the 3ph doesn't? If the loader also is gimpy, a common explanation for hydraulics that work for awhile, stop and then start working again after a rest is a clogged hydraulic filter, which would affect both the 3ph and loader.
I think the screen mentioned is in the high-pressure line after the loader (similar to some JD's and would affect only the 3ph, but I wouldn't think this type of obstruction would usually produce an intermittent failure. A clogged screen would obstruct the high-pressure line and probably would open the system relief valve. An open relief valve makes sort of a scream and it would be good to notice if that sound is present when the 3ph isn't lifting.
Nothing comes immediately to mind when thinking about a clang and then a variable delay before the 3ph stops, but maybe linkage is a candidate. On some position control 3ph's minor disassembly will expose the control valve. The lift spool and poppet valve ends can be seen, and working the 3ph lever will show whether the lift spool actually is moved into a lift position. It might be good to check the linkage and adjustments when the 3ph isn't lifting. Some tractors have a diverter valve that powers either the 3ph only or the loader plus 3ph. If there's a diverter valve, a good check when the 3ph isn't working would be to change the diverter valve to the 3ph only position (often called the remote, as opposed to the auxiliary position) to see if it starts working.
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| Skylark
Join Date: Posts: 1
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2003-01-26 48181
"I'll start by asking if the loader works when the 3ph doesn't?"
The loader works perfectly when the 3ph quits.
There is a position control if you mean can I adjust the height of that back blade. I can adjust it to wherever I want within it's range. ....
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| Jeff Earthwerks Unli
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2003-01-26 48194
You say the loader works when this happens, but does it work under load (fully loaded bucket cycling many times repeatedly)? I'm thinking that the pump may be aerating the hydraulic oil causing a loss in pressure either around the pistion rings of the 3pth piston or the pump itself. I have a hydrostatic backhoe that when it gets hot the hoe can't even lift itself. But if I cool the pump, the cylinders and the reservoir down using a garden hose it will work right away. Check the temperature of the oil right after the 3pth stops working by putting your hand on the reservoir (on my NH 33D it's the transmission/differential case) Remove the dip stick and see if the oil looks foamy. If yes try a different oil and check that the hydrauilc filter is renewed--that could cause a restriction causing aeration and lower pressure.
Is your machine hydrostatic drive? If yes over working it will cause heat build-up (make sure the oil cooler is not restricted regardless) ....
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| Skylark
Join Date: Posts: 1
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2003-01-26 48208
"but does it work under load (fully loaded bucket cycling many times repeatedly)?"
Yes I've gone on to move snow with the loader once the back blade quits and it keeps on lifting and pushing and doing what I ask of it for as long as I want.
Overheating sounds very plausible except wouldn't the front loader quit too? ....
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| Skylark
Join Date: Posts: 1
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2003-01-26 48209
And yep it's hydrostatic drive. ....
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| TomG
Join Date: Feb 2002 Posts: 5406 Upper Ottawa Valley
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2003-01-27 48229
A little orientation: Open centre hydraulic systems pump continuously in a loop and all valves--loader and 3ph are hooked in series around the loop. When a valve is operated, it blocks the loop and opens passages to the cylinders. Pressure develops and works against the load. Relief valves are in the loop and open when pressures reach maximum.
Failure can be due to the pump, valves or cylinders. What we're trying to do is figure if the pump or valves are the problem. Pump failure can be the result of the pump itself, obstructed high-pressure lines or obstructed or leaking suction lines. Suction line problems would produce foaming and overheating. Pressure would decline over a period of use and all hydraulics would develop little force. The problem would affect all hydraulics including the HST. A period of rest would restore function.
From the description, it doesn't sound like that's what's happening, although checking for foam and excessive heat as noted would be good. Hydraulic components become fairly warm when working but the pump, inlet and return lines from the loader valve should not become hot.
A relief valve should be opening if it's an obstruction problem. Here's a crude test for when both loader and 3ph are working. For the test you have to know the sound of an open relief valve. If the system is working normally, the system relief valve can be opened by holding a loader valve open until the loader moves to the limit of its travel and then a few seconds longer. There should be a squeal sort of like automotive power steering turned too far. More testing is needed if the squeal doesn't happen. There is a slight chance that a squeal would disappear when the loader valve is first operated. The test could be repeated when the 3ph isn't working.
Position control is a type of 3ph where the position of the 3ph lever is directly related to the height of the hitch. The lever usually rides in a semi-circular slot and there is a sliding lock that allows the hitch to be returned to the same depth after lifting. I asked the question because I was thinking about linkage and control valve problems. Hope at least some of this stuff is reasonably clear.
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| Skylark
Join Date: Posts: 1
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2003-01-27 48235
Yes thanks, we will have a look at this stuff when we get a chance. We won't have time until next week at this point and then I will report back how we made out. ....
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| TomG
Join Date: Feb 2002 Posts: 5406 Upper Ottawa Valley
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2003-01-27 48239
I forgot to mention that a tractor shouldn't be operated for prolonged periods with a relief valve open. It also can cause the oil to over-heat and over-heated oil can damage the pump. ....
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| Skylark
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2003-01-27 48242
Ok Tom, won't use the back blade until we get to the bottom of the problem. Thanks! ....
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| Skylark
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2003-02-11 49087
An interesting thing happened the other day. I took the Kubota out with the view to letting it jam up again..and when it did, I checked the hydraulic fluid for bubbles..there were none and the cylinder wasn't hot....so I moved the front loader a tiny bit and then tried to lift the back blade again and it moved! So that's my fix, but what's happening here? I only need to move the front loader an inch and then I can lift the back blade up until it stops lifting the next time. Obviously overheating is now discounted as th problem..so what is? I can live with the fix but I am curious. ....
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