Hydraulic cylinder leaking: rebuild or replace?

A hydraulic cylinder leaking oil at the rod almost always has a worn or damaged rod seal. A seal kit fixes the leak only when the rod, the tube and the mountings are still in good condition. If the rod is scored, pitted or bent, a new seal will fail again, and you need a new rod or a new cylinder.

This guide explains how to find the cause, when a rebuild is enough, and what to send us for a quotation. It supports our page on hydraulic cylinders for trucks, trailers and heavy equipment.

Hydraulic cylinder leaking: the common causes

Most leaks start at the rod seal, where the chrome rod moves in and out of the gland. Parker's cylinder troubleshooting guide and other industry guides point to the same few causes.

• Dirty oil. Hard particles in the oil cut the seal lips and scratch the rod. A damaged wiper seal also lets dust from the road or the mine site into the cylinder.
• Side load. If the cylinder is not in line with its load, the rod pushes hard against one side of the gland. This wears the seal, the rod bearing and sometimes the tube.
• A damaged rod. Scratches, pits and rust on the rod tear a seal every time the rod moves.
• Water or air in the oil. Water makes many seal materials harden at high temperature. Air bubbles under fast pressure changes can burn small marks into the seal.
• Poor fitting. A seal fitted the wrong way round, cut during fitting, or fitted without clean oil will leak early.

Leaks at the ports or hose ends are a different problem. Check the fittings and hoses before you open the cylinder.

Check the rod before you order a seal kit

The rod decides the repair. A seal kit replaces the parts that wear by design. It does nothing for the rod.

Clean the rod and look at it under good light along its full stroke. Look for lines along the rod, small pits, rust spots, and chrome that is lifting at an edge. Run a fingernail across any mark you find. If the nail catches, the mark is deep enough to cut a new seal.

Also look at how the old seal and guide rings wore. Even wear all round is normal service. Wear on one side points to side load. Then check the pins, the bushes and the straightness of the rod as part of the same job. A new seal or even a new cylinder will not fix a worn mounting.

Finally, look at the oil. Cloudy, milky or very dark oil means water or dirt is in the system. Change the oil and the filter, or the new seals will wear in the same way. You can find filters in our filters parts category.

Rebuild with a seal kit or replace the cylinder

Rebuild the cylinder with a seal kit when:

• the rod is smooth, straight and the chrome is intact
• the tube bore has no deep scoring
• the mountings and pins are in good condition
• the leak is the first one, not a repeat after a recent rebuild

Replace the rod or the whole cylinder when:

• the rod has deep scoring, pits or rust that catch a fingernail
• the rod is bent
• the tube is scored or the body is damaged
• the cylinder has leaked again soon after a rebuild

We supply hydraulic seal kits to rebuild HCIC and DMC cylinders. The Kaden seals listed in the HCIC range are rated for 40 MPa working pressure. Our catalogue also holds kits for other makes, such as the DMC seal kit for the DA130 cylinder, part number SEALKIT76245244, and kits from HYVA, Komatsu and Kato. Search them in the seals and gaskets parts category or in the parts search.

If the cylinder needs replacing, FDA is the sole agent in Indonesia for HCIC and DMC. For tipper trucks and trailers, see the underbody cylinder and the front-end tipping cylinder. For excavators, loaders and dozers, we arrange a custom hydraulic cylinder built to your drawing or to the old cylinder.

How to stop the next leak

A few habits make seals last longer.

• Keep the oil clean and change filters on time.
• Replace a torn wiper seal or rod boot quickly, before dirt reaches the rod seal.
• Keep the rod clean, and park with the rod retracted where the machine allows it, so less chrome is exposed to dust and rain.
• Check pins and bushes during service, and renew worn ones.
• Fit new seals with clean hands, clean oil and no sharp tools on the seal lips.

What to send for a quotation

To quote a seal kit or a new cylinder quickly, send us:

• the part number stamped on the cylinder, or the seal kit number if you have it
• the machine or trailer it fits, with model and year
• the bore, rod diameter, stroke and closed length
• the mounting type at both ends
• photos of the cylinder, the rod and the old seals

Attach the photos and details on our quotation form, and our sales team will reply with the right kit or cylinder.

Sources

• Parker Hannifin, Hydraulic cylinder troubleshooting
• Atos, Cylinders troubleshooting
• Dyco, Piston-rod surfaces, hard chromium and gland loading
• Yates Industries, Why is my hydraulic cylinder leaking