Boom Cylinder Repair & Resealing

Boom Cylinder Repair Across Machine Types

The boom cylinder carries the load your machine exists to lift. On a bucket truck it holds a lineman in the air. On a crane it holds the pick steady over the trailer. On an excavator it holds a loaded bucket over an open trench, and on a telehandler it holds a pallet of block three stories up. Ames Hydraulics does boom cylinder repair for all of them — boom lifts, bucket trucks, cranes, excavators, telehandlers, and truck-mounted booms — from our shop at 210 Freel Dr in Ames, Iowa. We tear the cylinder down, find what actually failed, fix that, and prove the repair holds pressure before it goes back on your machine.

This page covers the cylinder itself — tube, rod, piston, gland, seals, and the load-holding valving bolted to it. If the whole lift is acting up and you are not sure the cylinder is to blame, start with our boom lift repair page. And for the shop-wide process behind every cylinder on our bench, see our hydraulic cylinder rebuild page.

Why Boom Cylinders Drift

Cylinder drift is the complaint that brings most boom cylinders through our door. The boom settles overnight. The basket creeps down while somebody is working out of it. The stick will not hold grade, or the crane loses height under a suspended load. Drift means oil is escaping the side of the piston that carries the load, and that oil only has two ways out: past the piston seals inside the cylinder, or back through the valve that is supposed to lock it in place.

A boom cylinder leaking externally is the easy one to spot — oil streaking down the rod or pooling at the gland tells you the rod seals are done. Internal bypass is sneakier. The cylinder looks bone dry, the machine drifts anyway, and the operator gets blamed for leaving the boom up. Both problems trace back to the same short list of causes: seals hardened by heat and age, chrome damage chewing up seal lips, a scored bore from contaminated oil, or side loading that wore the cylinder unevenly.

Holding Valves and Counterbalance Valves

Nearly every machine that raises a boom over people or property carries a load-holding valve — most often a counterbalance valve mounted on or plumbed close to the cylinder. Its job is to lock oil in the cylinder when the control is in neutral, meter the boom down at a controlled rate, and keep the load from falling if a hose fails. When that valve will not seat — contamination on the poppet, a weak spring, a worn cartridge — the symptom looks exactly like bad piston seals: the boom drifts. A fair share of the "bad" cylinders that land on our bench test perfectly, and the real culprit is the valve. That is why we test before we tear down. A bench test tells us whether you need a boom cylinder repair, a valve, or both — before you have paid for either.

Reseal, Rebuild, or Replace

A boom cylinder reseal is the right fix when the hard parts are still good: straight rod, healthy chrome, clean bore, sound gland threads. We strip the cylinder, replace every seal and wear ring with a quality kit, and reassemble. It is the most economical repair there is, and on a cylinder that simply wore out from honest hours, it is all you need.

But new seals dropped into a scored bore or run over a pitted rod are wasted money — the same damage that wiped out the old seals cuts up the new ones in short order. That is when a reseal becomes a rebuild: honing the bore, repairing or replacing the rod, machining new parts where the originals are too far gone. A full boom cylinder repair costs more than a seal kit, but it is still a fraction of a new cylinder — and on older booms, a factory replacement can be a long lead time away or out of production entirely.

Sometimes replacement genuinely is the cheaper path, and when it is, we will tell you that before any work starts. You get a straight answer and a firm price up front, not a surprise on the invoice.

Rod Repair and Chrome

The rod takes the worst abuse on any boom. Machines that live outdoors get pitted chrome from weather and corrosion, side-loaded booms score and bend rods, and job-site contact leaves dents and dings. Every one of those imperfections drags across the rod seal on every stroke, and eventually the seal loses. Depending on the damage, we polish the rod, repair the surface, or machine a new one. We stock rod material in the shop, so a lift cylinder repair that needs a fresh rod does not sit waiting on a supplier.

Pressure Tested Before It Goes Back Under Load

Every boom cylinder repair that leaves this shop gets pressure tested first. We hold the cylinder under pressure on the bench and watch for bypass and drift, because on a component that holds a person in a basket or a load over a crew, "probably fixed" is not a standard. If the cylinder came in with its counterbalance or holding valve, we verify that too, so the whole load-holding package goes back proven, not assumed.

One Shop for the Cylinder and the Boom Around It

Boom cylinders rarely fail alone. The hoses feeding them chafe where they cross boom joints, pins and bushings wear oblong, and cracks show up around mounts that have been working loose for months. Because we are a full hydraulic and welding shop, boom cylinder repair here can roll straight into hose replacement, pin and bushing work, and structural repair without sending your machine anywhere else. Crane owners can see our crane boom repair page for the boom-side structural work that often goes along with cylinder trouble.

Get It Fixed in Ames

If your boom settles, your basket will not stay put, or there is oil where oil should not be, get the cylinder to us. We do boom cylinder repair for operators all over Ames and Central Iowa, with free pickup and delivery within 60 miles — and we take in cylinders shipped from well beyond that. Call or text 515-292-2599, or bring it to Ames Hydraulics at 210 Freel Dr, Ames, IA 50010, Monday through Friday, 7AM–5PM. We will find the leak, fix the cause, and pressure test the proof.