Down pressure after shutdown. I noticed my Bobcat 773C creates its own down pressure whenever it's shutdown

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little_fellow

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Oct 6, 2009
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I noticed my Bobcat 773C creates its own down pressure whenever it's shutdown. I had noticed this before but never paid much attention to it due to the fact that I generally leave the bucket flat on the ground when parking and the down pressure is minimum due to the fact that the cylinders are already in all the way. The other day I parked the skid steer with the bucket standing on its cutting edge . The next day, to my surprise, I found my skid steer standing on a 45 degree angle. The cylinders had pushed the bucket down until they were all the way in. I'm wondering if this is normal or is there something defective in the system?
 

brdgbldr

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This should not be possible with the engine off since the pump is what provides pressure to the cylinders and the valves should also not have been open.
Are you sure that someone isn't pranking you?
 
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little_fellow

little_fellow

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Yes I'm sure no one was messing with it. I had it locked up in the shed. It's been doing this for a long time just not as noticeable when the bucket was flat on the ground.
 

brdgbldr

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That is strange.
I can't even guess as to what would cause enough pressure to do that. Fluid expansion would have to be massive and on only one side of the cylinders. All I can think of is water in the hydraulic fluid but it would have to turn to steam to create that much pressure and then when it cooled off it would release the pressure. Maybe some other type of contamination with a more volatile fluid. But still only on one side of the cylinders not likely.
Hopefully someone on here can help.
 
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little_fellow

little_fellow

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That is strange.
I can't even guess as to what would cause enough pressure to do that. Fluid expansion would have to be massive and on only one side of the cylinders. All I can think of is water in the hydraulic fluid but it would have to turn to steam to create that much pressure and then when it cooled off it would release the pressure. Maybe some other type of contamination with a more volatile fluid. But still only on one side of the cylinders not likely.
Hopefully someone on here can help.
The oil is clean. No water in it and the machine's hydraulics all work beautiful. I thought maybe someone else on here noticed that on their machine.
 

Luthor

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I have had this happen on my 743 a number of times, it is a bit disturbing to open the shed in the morning and find the Bobcat standing at an angle.
 
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little_fellow

little_fellow

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The oil is clean. No water in it and the machine's hydraulics all work beautiful. I thought maybe someone else on here noticed that on their machine.
I have had this happen on my 743 a number of times, it is a bit disturbing to open the shed in the morning and find the Bobcat standing at an angle.
It alarmed me because I had the skid steer in a tight fit shed with a pad lock in the centre of 2 hinged doors. When I got there the pad lock mechanism was broke and the back end of the skid steer was sticking out . I thought someone had broken in and then I realized what had happened. Could of been worse. Could have been crushing something valuable.
 
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Luthor

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That is very similar to what happened with mine, the engine compartment door of the Bobcat was pushing against the sliding door of the shed making it very hard to open.
 
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little_fellow

little_fellow

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That is very similar to what happened with mine, the engine compartment door of the Bobcat was pushing against the sliding door of the shed making it very hard to open.
I'm guessing that if you don't want this to happen, you have to drain all back pressure by turning the ignition key all the way counterclockwise and then do all the hydraulic functions till all the hydraulic pressure is drained . I should try this to see if it works.
 
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ajwgator

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Oct 12, 2005
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I had this happen on my 843 back in 2007.
I just blamed it on air after a hose change on one of the cylinders.
 
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little_fellow

little_fellow

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I feel better to know this. It must be a flaw in the system and not a problem with my own machine in particular. I'm guessing that's why most of the time I have difficulty attaching the quick couplers on the auxiliary hydraulics.
 

spitzair

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Dec 17, 2009
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Very common for this to happen with the way these machines are balanced. When you have no load in the bucket the majority of the weight of the machine is on the rear axle. When you put the bucket down on the ground with then cutting edge aimed straight down the weight of the bucket and arms is essentially taken off the front wheels. When the hydraulics bleed off over time what little pressure remains in the rams to hold the front wheels down and weight of the bucket and arms up will bleed off and now that the weight of the bucket is supported by the ground the machine tips backwards due to the remaining majority of the weight being behind the rear axle and over she goes. This is one of the big reasons you need to put supports under the rear of the machine when tipping the cab back especially with no attachment on the front… clear as mud eh?
 
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little_fellow

little_fellow

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Very common for this to happen with the way these machines are balanced. When you have no load in the bucket the majority of the weight of the machine is on the rear axle. When you put the bucket down on the ground with then cutting edge aimed straight down the weight of the bucket and arms is essentially taken off the front wheels. When the hydraulics bleed off over time what little pressure remains in the rams to hold the front wheels down and weight of the bucket and arms up will bleed off and now that the weight of the bucket is supported by the ground the machine tips backwards due to the remaining majority of the weight being behind the rear axle and over she goes. This is one of the big reasons you need to put supports under the rear of the machine when tipping the cab back especially with no attachment on the front… clear as mud eh?
That makes all the sense in the world. Thanks for the input. This might even help people avoid a potential hazard.
 

ajwgator

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Makes perfect sense spitzair....and especially the rear supports when tipping the cab back!
 
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