Hydraulics get weak over time....

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da29647666

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Apr 5, 2008
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Hi all - I recently bought a used Bobcat 630. I was moving a large pile of recycled concrete today and had no problems. After just over an hour, the hydraulics started getting really weak. I noticed the bucket loads had to be smaller and it got to a point where I couldn't lift a loaded bucket at all. I let it rest over night and it was fine this morning, until again, after about an hour of use. What's going on? I ran at full throttle the whole time. The machine uses 10w30 oil as hydraulic fluid. It is full. Is this oil getting too hot? Is it breaking down? I don't see any leaks any where. Can I use regular hydraulic fluid in a machine who's owner's manual calls out for oil? Can I mix them or do I have to drain the oil first? Any advice is greatly appreciated. Thanks for your time - Dave.
 

Bandit1047

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I am NO expert but I know if your oil is getting overheated it will loose it's ability to build pressure. Sears sells an inferred (non contact) heat reading gun for about$79.00. It is great for checking oil temperature and any other heat source. If your oil is over 170F you may be overheating. The unit may have the wrong oil in the hydraulics and it may have a viscosaty that is to low. Just my 2 cents worth.
 

Tazza

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I am NO expert but I know if your oil is getting overheated it will loose it's ability to build pressure. Sears sells an inferred (non contact) heat reading gun for about$79.00. It is great for checking oil temperature and any other heat source. If your oil is over 170F you may be overheating. The unit may have the wrong oil in the hydraulics and it may have a viscosaty that is to low. Just my 2 cents worth.
Does its drive loose power too? or just hydraulics?
It would be a good idea to check your oil cooler, just make sure its not all plugged with crud.
The hydraulic pump could be a bit worn causing lower hydraulic flow when the oil thins out. You can buy hydraulic pump re-build kits. Does it still have the same lifting power when warm? just slower? If it still has the power its not your relief as you are still getting pressure but if its slow that makes me think possible pump wear.
Any howling? jittery operation?
 
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da29647666

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Does its drive loose power too? or just hydraulics?
It would be a good idea to check your oil cooler, just make sure its not all plugged with crud.
The hydraulic pump could be a bit worn causing lower hydraulic flow when the oil thins out. You can buy hydraulic pump re-build kits. Does it still have the same lifting power when warm? just slower? If it still has the power its not your relief as you are still getting pressure but if its slow that makes me think possible pump wear.
Any howling? jittery operation?
Thanks. It drives fine. The cylinders just get weak. It doesn't have the same lifting power at all. No howling. Not jittery. Thanks for your input.
 

Tazza

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Thanks. It drives fine. The cylinders just get weak. It doesn't have the same lifting power at all. No howling. Not jittery. Thanks for your input.
Sounds like your hydraulic pump is worn. As the oil warms up it gets thinner, thinner oil means it by-passes easier. You could pull the pump off and check it for internal wear. It will most likely be a vane pump, scratches that run around the cam plate are fine, the biggest issue is what looks like chattering marks. If there are marks your problem is the vanes are un-able to stay in contact with the cam plate at all times to generate pressure. They sort of skip over the top, this is where your pressure would be going if its worn. Wear on the front and rear housings can be an issue too.
The only way to test it short of pulling the pump is to get it pressure and flow tested. They remove the high pressure hose and attach a test unit to load the system down and check flow rates. Never just stick a pressure gauge here, there is no relief valve and you will do damage to yourself or the pump.
 
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da29647666

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Sounds like your hydraulic pump is worn. As the oil warms up it gets thinner, thinner oil means it by-passes easier. You could pull the pump off and check it for internal wear. It will most likely be a vane pump, scratches that run around the cam plate are fine, the biggest issue is what looks like chattering marks. If there are marks your problem is the vanes are un-able to stay in contact with the cam plate at all times to generate pressure. They sort of skip over the top, this is where your pressure would be going if its worn. Wear on the front and rear housings can be an issue too.
The only way to test it short of pulling the pump is to get it pressure and flow tested. They remove the high pressure hose and attach a test unit to load the system down and check flow rates. Never just stick a pressure gauge here, there is no relief valve and you will do damage to yourself or the pump.
You're awesome. Thanks man.
 

Tazza

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You're awesome. Thanks man.
Please do know, its what i *think* it is, i may be wrong. The symptoms do fit. I personally would pull the hydraulic pump off (2 bolts at the front of the main pump). It will simply slide forward. Before you do this, drain as much fluid as you can as you will loose pretty well all of it with the hydraulic pump removed. I drain by fluid by running the machine at idle and operating the aux hydraulics to drain the fluid to a drum, when it starts to jitter or foam, shut down. You will still loose oil, but no where near as much.
Good luck!
 

sterlclan

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Please do know, its what i *think* it is, i may be wrong. The symptoms do fit. I personally would pull the hydraulic pump off (2 bolts at the front of the main pump). It will simply slide forward. Before you do this, drain as much fluid as you can as you will loose pretty well all of it with the hydraulic pump removed. I drain by fluid by running the machine at idle and operating the aux hydraulics to drain the fluid to a drum, when it starts to jitter or foam, shut down. You will still loose oil, but no where near as much.
Good luck!
I have the same machine it is a vane pump you can get parts here
http://stores.ebay.com/skidloader-h..._W0QQcolZ4QQdirZ1QQfsubZ9685124QQftidZ2QQtZkm
good luck ...Jeff
 
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