Case 580c boom leak

[Dennis Koelling]

When the backhoe boom is unlocked, it will slowly lower to the ground. However, the boom can be used to lift the drive wheels off the ground, and will hold this position. This tells me the boom cylinders are not leaking internally, but perhaps a leak in the control valve is present. Would the leak be at the load check poppet or spool? What is the most common cause of this internal leak? Is it possible to install a new load poppet without removing the entire valve stack?

 

[Roger (Mi)]

Some settling of the boom is the nature of the beast. That's why there is a boom lock or chains to hold the boom up. Even though the boom is working properly, the boom seals can still have seepage. Poppets? There are secondary reliefs on the valve spool for the boom (other spools have their reliefs too). It's unlikely that serious leakage will occur there unless there is a broken relief spring. Valve spools wear and will have some internally seepage. When it gets excessive, the valve spool will need to be replaced. Replacing a valve spool is a good day's project. Consider replacing the boom seals first. Even so, don't expect the boom to stay up over night.

 

[Dennis Koelling]

Thanks so much for your reply! You have a great point, in that the boom piston seal could still be leaking, perhaps in one direction due to the design of the seal. Hope to hear from you again in the future.

 

[Anonymous-0]

Probably just seepage past the seals when the system is static. I just recently rebuilt the swing tower & all the cyls on my 580B. One of my stabilizer cyls will slowly weep down from the up position over 4-5 days, Sit the machine up on them & that same stabilier will hold position indefinetly.I believe the seal design (V rings) need a bit of pressure behind them to seal tightly to the cyl bore.

 

[Dennis Koelling]

I believe your point about pressure on the piston seals is accurate. I just remembered, however, about an important fact about double-acting cylinders: unequal volume on the rod side of the piston vs. the opposite side. The piston cannot [weep] to the retracted position because the bolt side of the piston has more volume than the rod side. This would explain how the piston would leak one way and not the other. Thanks so much for your reply!