I recently had my bucket tilt cylinder rebuilt because it was leaking down slowly. After reinstalling and testing it continues to leak down so I had all lines replaced that connected to that cylinder from front to rear. It continues to leak down. I have noticed that when the unit is running and the bucket is leaking down I can lift the operators bar and the bucket will stay in position and will not leak down. I have no other ideas of what to replace or repair unless there is a valve of some sort that needs adjusting or repaired. I have also noticed that the machine is beginning to creep forward. Any advise will be greatly appreciated.
Bobcat 753 Bucket leakdown
- Thread starter Gwenssin
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glastron23
Silver Member
a cylinder with a seal problem will not leak down on it's own, the oil needs to return to tank before it will lower... the spool valve must be leaking, when you open the operators bar this shuts off the controls their fore locking the cylinder
Watch this video and you will see, i really like this guy... use him all the time...Jim Hydraulic Cylinder Myth Exploded
Watch this video and you will see, i really like this guy... use him all the time...Jim Hydraulic Cylinder Myth Exploded
AKKAMAAN
Veteran Member
Good catch jim!
Here is the directory with all the flash video clips the Aussie , Brendan Casey have posted on his Hydraulic Supermarket
glastron23
Silver Member
i really like this guy... he's very informative and is interesting...Jim if you go to http://www.hydraulicsupermarket.com/technical.html then on the left side is the Technical library... LOTS of INFO
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Wayne County Hose
Veteran Member
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- Aug 24, 2007
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- Massey Ferguson model 85, Allis-Chalmers WD-45
Interesting. Then I wonder why the HUNDREDS of cylinders I have rebuilt for customers that they complained were leaking down did not leak down after I rebuilt them. Theory and real world are two totally different places. I have also found numerous holes in Mr Casey's theories. Be careful, sometimes what is written very nicely and sounds so true is sometimes so wrong. Mr. Casey recommends you also take your suction strainer out and throw it away. Well, I'm waiting to see the pile of them.
J_J
Super Star Member
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- Power-Trac 1445, KUBOTA B-9200HST
Gwenssin,
Our Power-Tracks are driven by a hydrostatic transmission, and hyd wheel motors. The transmission is controlled by a Morse cable assembly, and a foot pedal and linkage setup, and sometimes binds. Try going over all the linkage, and clean and lube everything well. I have to put my PT up on blocks to adjust the linkage. Do you have a hyd schematic for your Bobcat?
Does the operators bar only with engine running, or will it stop the cylinder from dropping with engine off. There may be a pilot operated check valve in the circuit to prevent the cyl from dropping.
I always thought that if the cyl had an internal leak, that the cylinder would move until the pressure equalize, as illustrated by the computer generated simulation.
Our Power-Tracks are driven by a hydrostatic transmission, and hyd wheel motors. The transmission is controlled by a Morse cable assembly, and a foot pedal and linkage setup, and sometimes binds. Try going over all the linkage, and clean and lube everything well. I have to put my PT up on blocks to adjust the linkage. Do you have a hyd schematic for your Bobcat?
Does the operators bar only with engine running, or will it stop the cylinder from dropping with engine off. There may be a pilot operated check valve in the circuit to prevent the cyl from dropping.
I always thought that if the cyl had an internal leak, that the cylinder would move until the pressure equalize, as illustrated by the computer generated simulation.
glastron23
Silver Member
Hi Wayne .. i too have rebuilt many cylinders, the majority on boom/bucket trucks with close mounted holding valve, these are very hard to find internal leaks, the majority will have rod seal leaks long before internal leaks are suspected. We have modified cartridges to help with this problem.
The majority of the cylinders come in with poor lifting power due to the seal leak, some have internal tube noise when being used and some show hot spots on the cylinder tube where the fluid has been leaking by for a while.
Yes i have rebuilt non-holding valve cylinders that drift and the problem goes away, but this doesn't mean that the valve bank wasn't leaking. If the seals are leaking and no valve leak, no drift. if the seals are not leaking and the pressurized side of the valve is, drift. If the seals are leaking and the unpressurized side of the valve is leaking, drift.
hydraulic repair is a black art and if the pot is stirred enough then it's amazing to see just what floats to the top!!!
As far as suction filters we have boxes of them out of new lifts, want some... If you start with a clean system, use a GOOD return filter with a GOOD beta rating and maintain it, then a 100 mesh or large micron suction filter is restriction i can live without. Jim
The majority of the cylinders come in with poor lifting power due to the seal leak, some have internal tube noise when being used and some show hot spots on the cylinder tube where the fluid has been leaking by for a while.
Yes i have rebuilt non-holding valve cylinders that drift and the problem goes away, but this doesn't mean that the valve bank wasn't leaking. If the seals are leaking and no valve leak, no drift. if the seals are not leaking and the pressurized side of the valve is, drift. If the seals are leaking and the unpressurized side of the valve is leaking, drift.
hydraulic repair is a black art and if the pot is stirred enough then it's amazing to see just what floats to the top!!!
As far as suction filters we have boxes of them out of new lifts, want some... If you start with a clean system, use a GOOD return filter with a GOOD beta rating and maintain it, then a 100 mesh or large micron suction filter is restriction i can live without. Jim
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