453F Air in Hydraulic system

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OldMachinist

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I have a 200 453F with 1600 hrs. that is driving me crazy. If you read Hoss54's thread from back in Feb. the problem he describes is exactly what I have same actions and noises. He didn't post back if he ever figured it out so I'm starting this thread. I've pulled the poppets from the filter block, cleaned the main relief and check every where for leaks it doesn't leak a drop anywhere, oil and filter are new. I can't find any reference to a drain filter on this machine in ether the service manual or the parts lists. The drive side is fine. I am going to check the charge and system pressures tomorrow but I just thought somebody might have some other ideas.
 

OldMachinist

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Thought I hit the General Repairs when I posted this. Maybe a Moderator can move it over there.
 

OldMachinist

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Thought I hit the General Repairs when I posted this. Maybe a Moderator can move it over there.
I forgot to put a link to Hoss54's original thread so here it is. http://www.skidsteerforum.com/DesktopDefault.aspx?tabid=54&frmView=ShowPost&PostID=2329
 

Tazza

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I forgot to put a link to Hoss54's original thread so here it is. http://www.skidsteerforum.com/DesktopDefault.aspx?tabid=54&frmView=ShowPost&PostID=2329
I really can't see how air could enter the system if the oil level is correct and there are no leaks. Did it just start having this problem? or has it been doing it for a long time?
I have noticed purging the air from my 743 has taken quite a long time and its still not rite. I had the lift arms working well, but when i attached the tilt cylinder i now have air back in my lift arms. Could it simply be air traped in the system that will eventually bleed out?
Can you give me a bit more info on the history of the problem?
The hydraulic circuitry is a closed loop with the reserve above the pump, there is no way i can see for air to be drawn in. No hoses run at a negative pressure to draw air in, they are all at charge pressure or higher (except the hose to the reserve tank that just has gravety against it).
There has to be an answer, as there are 2 people on this forum alone that have this problem, surly there will be more around.
One thought, the only other thing i could think of is bad ram seals. All the rams are double acting, this means you need constant pressure against the pressure seal for it to seal against the rod. If you have a load on the ram and move the spool when the engine is off, i guess there is a chance it could draw in air (still very low i would guess) as the rod retracts causing a low pressure at the seal and sucking in air?? Its just a thought.
 

OldMachinist

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I really can't see how air could enter the system if the oil level is correct and there are no leaks. Did it just start having this problem? or has it been doing it for a long time?
I have noticed purging the air from my 743 has taken quite a long time and its still not rite. I had the lift arms working well, but when i attached the tilt cylinder i now have air back in my lift arms. Could it simply be air traped in the system that will eventually bleed out?
Can you give me a bit more info on the history of the problem?
The hydraulic circuitry is a closed loop with the reserve above the pump, there is no way i can see for air to be drawn in. No hoses run at a negative pressure to draw air in, they are all at charge pressure or higher (except the hose to the reserve tank that just has gravety against it).
There has to be an answer, as there are 2 people on this forum alone that have this problem, surly there will be more around.
One thought, the only other thing i could think of is bad ram seals. All the rams are double acting, this means you need constant pressure against the pressure seal for it to seal against the rod. If you have a load on the ram and move the spool when the engine is off, i guess there is a chance it could draw in air (still very low i would guess) as the rod retracts causing a low pressure at the seal and sucking in air?? Its just a thought.
Well it started out early last month with the lift being a little jerky but not all the time. Then the oil started getting foamy. I changed the oil and filter at that point not knowing the exact history of the last oil change. Took a little longer to get foam after that. Now I should add that I only use this machine around the farm so it sits 5 out of 7 days. Used it pretty heavy towards the end of the month and the lift and bucket where jerky and slow when I got done with project. Now is jerky all the time. Hoss54 described it perfectly right down to gurgles after shut down. Seems to be a little better if I don't run at full RPMs. I will add that when I take the filter block drain plug out no oil drains out. I've checked for flaps in hoses, replaced orings and checked all connections. Like I said I'm going to check pressures tomorrow when the gauges I ordered get here.
 

OldMachinist

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Well it started out early last month with the lift being a little jerky but not all the time. Then the oil started getting foamy. I changed the oil and filter at that point not knowing the exact history of the last oil change. Took a little longer to get foam after that. Now I should add that I only use this machine around the farm so it sits 5 out of 7 days. Used it pretty heavy towards the end of the month and the lift and bucket where jerky and slow when I got done with project. Now is jerky all the time. Hoss54 described it perfectly right down to gurgles after shut down. Seems to be a little better if I don't run at full RPMs. I will add that when I take the filter block drain plug out no oil drains out. I've checked for flaps in hoses, replaced orings and checked all connections. Like I said I'm going to check pressures tomorrow when the gauges I ordered get here.
Okay here are the rusults of my pressure tests.
Charge pressure 80psi steady. Service manual says 75-85psi
Hydraulic system was 1350psi book says 1195-1245psi.
System pressure was tested at aux. quick coupler like the book says.
I adjusted system pressure to specs.thought that might have fixed it but problem returned as soon as I drove it around some and the oil warmed up. Pressure was probably off from me cleaning relief valve.
The service manual I have has two different pages saying where to check the charge pressure. One dated 5/97 and a revised page from 9/97 the results above are from the revised location using the charge pressure switch port. The page from 5/97 says to check it at the filter block drain port. I checked it at the drain port also and the pressure was 120psi. But I'm assuming the revised location is what they really wanted.
I had a tee with a valve and a piece of clear tubing in my test line below the gauge so that I could see what the oil looked like at both loacations and at the drain port I had good flow with lots of air. The switch port didn't seem to have any flow at all.
Well I'm done working on it for awhile until I can think of anything else or somebody suggests something.
 

Mr Jimi

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Jan 30, 2006
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Okay here are the rusults of my pressure tests.
Charge pressure 80psi steady. Service manual says 75-85psi
Hydraulic system was 1350psi book says 1195-1245psi.
System pressure was tested at aux. quick coupler like the book says.
I adjusted system pressure to specs.thought that might have fixed it but problem returned as soon as I drove it around some and the oil warmed up. Pressure was probably off from me cleaning relief valve.
The service manual I have has two different pages saying where to check the charge pressure. One dated 5/97 and a revised page from 9/97 the results above are from the revised location using the charge pressure switch port. The page from 5/97 says to check it at the filter block drain port. I checked it at the drain port also and the pressure was 120psi. But I'm assuming the revised location is what they really wanted.
I had a tee with a valve and a piece of clear tubing in my test line below the gauge so that I could see what the oil looked like at both loacations and at the drain port I had good flow with lots of air. The switch port didn't seem to have any flow at all.
Well I'm done working on it for awhile until I can think of anything else or somebody suggests something.
I am probably wrong but, when I changed my 3/4 inch by 51 inch hydraulic line, I asked the guys at the shop how to bleed the air out and they said run your all the hydraulics all the way both ways a few times and they will clear themselves? I hope that helps you
Jim
 

OldMachinist

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I am probably wrong but, when I changed my 3/4 inch by 51 inch hydraulic line, I asked the guys at the shop how to bleed the air out and they said run your all the hydraulics all the way both ways a few times and they will clear themselves? I hope that helps you
Jim
The more I cycle it all the way the worse it gets.
 

dstan359

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Jan 27, 2012
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The more I cycle it all the way the worse it gets.
Just purchased 453 and I'm having the same problem with air. The bobcat dealer said I need to replace gear pump and hydro pumps that air may have damaged both of them . The machine only has 800 hrs. They gave me a quote of 7800 to fix. A mechanic who works on these said he thinks it's the gear pump because it drives, turns fine . what should I do? Change the gear pump and start there.
 

OldMachinist

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May 24, 2006
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Just purchased 453 and I'm having the same problem with air. The bobcat dealer said I need to replace gear pump and hydro pumps that air may have damaged both of them . The machine only has 800 hrs. They gave me a quote of 7800 to fix. A mechanic who works on these said he thinks it's the gear pump because it drives, turns fine . what should I do? Change the gear pump and start there.
It may only be sucking air at the connection of the suction hose to the tank. That's what I found on mine. Problem is it's very hard to get to. It's back behind the battery at the bottom of the tank. Any idea of how long someone has been running this way?
 

mrdeere1959

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Nov 1, 2011
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It may only be sucking air at the connection of the suction hose to the tank. That's what I found on mine. Problem is it's very hard to get to. It's back behind the battery at the bottom of the tank. Any idea of how long someone has been running this way?
what hyd oil are you using? needs to be high quality anti-forming oil
 
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