rScotty
Super Member
- Joined
- Apr 21, 2001
- Messages
- 8,336
- Location
- Rural mountains - Colorado
- Tractor
- Kubota M59, JD530, JD310SG. Restoring Yanmar YM165D
The piston in the cylinder has some type of seal to divide the cylinder. If that seal leaks the oil bypasses the piston from the loaded end to the opposite end and the cylinder leaks down, with no visible leakage. As i stated before listen to the cylinders.
Thinking about the control vlave the spools operate in oil, so unless you have foreign material in the oil there should be very little if any wear.
If replacing the seals on the pistons helps for a little while as you stated then how is it the valve? The seals in the cylinder move the length of the barrel unlike a valve that moves a very short distance. If the seals wear ouut quickly then the cylinder needs replaced or you have abrasive junk in the oil.
As for the valve unless it has had foreign material pass thru it and the spool was forced with dirt between the lands there should be no or very little leakage past the spools, that is provided the spools properly center.
I am a cheap skate and before I replace high dollar parts I make sure they are truely at fault. To check if it is the cylinders pllumb a shut off valve into the lift side of the cylinders and raise the loader shut the valve and see if it still lowers. That may save you a few hundred dollars.
Here is a simple thought experiment:
Suppose we take any cylinder off the tractor and put it on the bench. Take it apart and remove the seal from the piston completely.
Now reassemble the cylinder so as to put that piston without any seal roughly at midpoint, and fill both sides with oil/hydraulic fluid. What we have now is a cylnder with the world's worst piston leak. The poor thing is missing the seal entirely. That piston can literally rattle in the bore. But other than that, it's a pretty common FEL loader lift arm cylinder. We've all seen cylnders sort of like that because the seals were either torn up or so hardened they didn't work anymore.
OK, that cylinder is sitting there filled it with oil and the next step is to keep it full as we plug or cap both cylinder ports.
What we have now is a cylinder full of fluid with a very leaky piston but no way for fluid to escape.
Now try to push the rod end into the cylinder bore just like would happen if it were leaking down. I'm betting you cannot push the rod in more than a fraction of an inch no matter how much force you use.
Why do I think that?
rScotty