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Bob, when you say to check pressure between the pump and valve set, would the ports be the correct location? We did notice with the bucket raised and motor off, that the bucket would have a creaking noise as (I assumed) it was slowing dropping. Also, not clear on your directions to find the bad one. Will it drop faster than the one that is still good, or if they both drop at the same rate then seals in both should be replaced? My neighbor has one set of seals on order from the local JD dealer at $70+tx, is there somewhere else that might be less $'s? Since we are fairly certain the issue is the lifting cylinders, maybe best to replace both side right away?
The ports are a correct location. Between the pump and valve set is the easier of the two best locations. The difference is that at the ports you can't read the pressure needed to operate the cylinder because you can't plug the cylinder in when the gauge has already occupied the port.

The point of a pressure test in this case is to find the relief pressure, and to determine if there is a problem with the cylinders. The relief valve is immediately after the pump and before fluid is diverted to a port by the control valve, and cylinder pressures can't be determined unless the cylinders are online.

The primary purpose of a relief valve is to protect the pump from overpressure.

With the gauge between the pump and valve set, the relief setting can be observed by extending or retracting cylinders until they bottom out at the end of their stroke, In addition, the actual pressure to raise/lower the cylinders can be observed in real time for either direction of cylinder travel for any of the spools of a valve set without the need to move the gauge.

Some pumps and some valve sets come with a gauge port to make installing a gauge easier.

The creaking noise that you heard with the bucket raised is due to fluid leaking past the seals allowing the cylinders to relax.

In the single cylinder test that I outlined, if the cylinder being tested does not drop, the seals are fine and the seals in the cylinder that was disconnected need to be replaced. If the cylinder under test drops, then the test should be redone with the other cylinder to determine the condition of it's seals.

Any hydraulics shop and many auto parts stores will have the seals for considerably less than the $70 that the dealership wants. I recently replaced all but the dust seal in one of the lift cylinders for my SCUT for C$9.14 (less than US$7) at The Parker Store locally. My dealer wanted US$30 for the set.
 

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Discussion Starter #42
A big THANK YOU to AOW162435/Andreas! Shims arrived today, hopefully I get a chance to put them in tomorrow.

Also, thank you to Tudor for your expert advice and to everyone else who chimed in.

After I get back from vacation, it'll be time to tackle the cylinder(s) rebuild.
 

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No problem. Any time that I can help.
 
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