Piston Seal Replacement

[Mad Dog]

I picked up a used Kioti DK35 with an SMC 75 backhoe. The piston seals on the support legs are leaking and I'd like to get them replaced. They are leaking enough that the legs will start to drop after a few days in the upright position. I'm new to tractors and hydraulics, but do most of my own repair work. to remove the piston, do I just need to remove the lines and take it to a hydraulic shop? What abour reinstallation? Does the system need to be bled in anyway?

Thanks

 

[J_J]

The hyd system will self bleed as you use the machine.

Might take about 5 to 10 full cycles to purge all the air.

 

[Farmerford]

Brendan:

Cylinders that "start to" leak down after a "few days" may have a piston leak as you suspect, but that sort of slight leakage can also occur (in fact is typical) in the directional control valve itself. Spool valves by nature do not completely block the flow of fluid into or from the cylinder; the spools are typically hand fitted to the valve body, and if you get a tight one it may leak almost none, but if you get a loose one it can leak quite a but an still be within specificatios. You might want to check for a piston seal leak first. Extend or retract the cylinder fully, then remove from the control valve the hose that connects to the cylinder closest to the piston in that position, point the hose into a bucket, and then shift the valve to put pressure on the cylinder in the same extended or retracted direction. The piston will not move because it is at the limit of travel, but if fluid is escaping around the piston it will show up as a dribble (or a flow if the piston seal is really worn) from the disconnected hose.

 

[Mad Dog]

Thanks for the detailed response. The seals are definetely leaking, I can see it when they are extended and have a load on them. They weep quite a bit.

 

[dfkrug]

The seals are definetely leaking, I can see it when they are extended and
have a load on them. They weep quite a bit.

That's the gland seal, and these often get damaged when operating the cylinder over scratched
or rusty rods.

You can't really tell if the piston seals are bad unless you disconnect a hose as mentioned above,
or detect (by sound or temp rise) the oil rushing past the piston seals when attempting to
lift a load.

The valve has no seals and is designed to leak somewhat as it is only a spool inside a cylinder with
a few thousandths clearance.

If your outriggers take a few days to leak down, that is actually pretty good valve performance.

If your gland seal is so bad that the outrigger can not hold the tractor up and you lose a lot of
oil, then you DO need to fix at least that seal.

 

[Mad Dog]

They hold the tractor up, but I can see hydraulic fluid leaking out. I just assume fix it. I did notice some nicks and scratches on the piston rod that could easily be smoothed out.