SPARE PARTS KIT

551 908 77B SPARE PARTS KIT is usually one of those critical internal seals, often found deep inside a hydraulic cylinder on a feed beam or perhaps a boom articulation point. Its main gig is to keep the high-pressure oil exactly where it needs to be, preventing any internal leakage that would otherwise mess with your cylinder's ability to hold position or move with consistent force. It’s essentially what makes sure your rod extends and retracts properly under load.

When this seal starts to wear out, or if it gets nicked during an assembly, you’ll definitely notice things getting a bit sluggish. Usually what happens is the cylinder will start to drift, especially under load – say, your feed beam slowly creeps down when it should be holding steady. Or, if it’s on a boom, you might find it just doesn't hold its position as well, making fine adjustments a real pain. Sometimes you’ll even hear a faint internal bypass noise, a sort of low hiss, if the leak is significant enough.

When you’re swapping one of these out, the biggest thing is to make absolutely sure the bore and rod are spotless and free of any burrs or sharp edges from the old seal. A tiny scratch on the new seal during installation means you’ll be doing the job again real soon. And don't forget to properly lubricate the new seal with clean hydraulic oil before you even think about pushing it into place; that little bit of lube makes all the difference in getting it seated right without damage.