A weekend restorer down in southwest Iowa — the area around Council Bluffs and Red Oak — called us about automotive two post lifts and a leaky cylinder he’d been fighting on a used lift he’d bought at auction. He was doing frame-off restoration work on a 1970s C10 and a mid-’80s Bronco, and the lift kept drifting a couple inches over the course of an evening’s welding session. That drift is the classic sign of a cylinder seal issue, and it’s fixable — but only if you know what you’re looking at and what parts to source. This checklist walks through everything a serious hobbyist needs to know about hydraulic cylinders on a two-post lift, whether you’re buying used or maintaining what you already own.
New Rotary and Challenger 2-post lifts with factory-fresh cylinders, plus rebuild kits and seal kits for older units. Call 800-674-9302 for restoration-shop advice.
Why Cylinders Are the Common Failure Point
On automotive two post lifts, the hydraulic cylinders are the working muscles of the whole system. They’re also the first components to show wear, because seals live inside a moving cylinder full of hot fluid and take the direct force of every lift cycle. A cylinder that’s 15 years old and has served in a commercial shop probably has at least one worn rod seal, and possibly a worn piston seal too. That doesn’t make the lift junk — it makes it a rebuild candidate. But you need to know before you buy or before you commit to a season’s worth of restoration work.
The southwest Iowa restorer had picked up his lift at a farm auction for a great price. What the low price didn’t tell him was that both cylinders had drifted enough over storage that the seals had taken permanent sets. When he raised the lift under load, it would hold for about 20 minutes before starting to creep. That was fine for oil changes but genuinely bad for extended welding work where he needed the vehicle rock solid overnight. His decision was whether to rebuild or replace, and this checklist is what got him to the answer.
Step One: Identify the Cylinder Type
Automotive two post lifts use two broad cylinder styles: direct-drive (where the cylinder sits inside the column and pushes the carriage directly) and cable-driven (where a smaller cylinder drives one column and cables transmit force to the other). Each style has slightly different seal kits, and rebuild parts are not interchangeable between them. Before you order anything, identify which style your lift uses. Rotary SPOA10 and Challenger CL10 are both direct-drive designs; older BendPak XPRs and some imports use cable-driven layouts.
Cylinder identification also includes bore diameter, rod diameter, and stroke length. Those three numbers determine the seal kit part number, and they’re usually stamped on the cylinder body or listed in the operator manual. On the southwest Iowa lift, we needed a caliper to measure bore because the stamp had rusted illegible. That took ten minutes and gave us the number we needed to order the correct kit. This step is annoying but non-negotiable — the wrong seal kit is expensive to ship back.
Step Two: Diagnose Where the Leak Is
A cylinder can lose fluid at three places: the rod seal (external leak, visible fluid running down the cylinder body), the piston seal (internal leak, no visible fluid but the lift drifts under load), or the port fittings (external leak at the hose connection). Diagnosing which one is failing tells you whether you need a seal kit, a full cylinder rebuild, or just a fitting change. Confusion between these three costs weekend restorers a lot of frustration.
The southwest Iowa lift had no visible external leak. That ruled out rod seals and port fittings and pointed directly at the piston seal. To confirm, we raised the lift, engaged the mechanical safety cams, cracked the release valve, and watched to see if fluid flowed backward through the pump. It didn’t, which confirmed the drift was internal cylinder bypass. That single diagnostic step saved ordering the wrong parts and lets you plan the rebuild with confidence. Every rebuild diagnostic should start there before any wrench touches the cylinder.
Step Three: Source the Right Rebuild Kit
Rebuild kits for major-brand automotive two post lifts are widely available and reasonably priced. Rotary, Challenger, and BendPak all publish part numbers and stock kits through their US distributor networks. We keep the common kits on the shelf here in Ames — SPOA10, CL10, SPO12, CL12 — and ship them nationwide. Off-brand cylinders can be trickier. Some imports don’t stock seal kits at all, and you end up with a generic hydraulic-supply seal set that requires cross-referencing bore and rod dimensions. That’s still doable, but it takes patience.
The southwest Iowa lift turned out to be a Rotary SPOA9 from the early 2000s, so the kit was in stock and ran about $85 per cylinder. Total parts for both cylinders came in under $200. The alternative — replacing both cylinders complete — would have been closer to $1,200. That is the delta a rebuild-friendly brand offers over its lifetime, and it’s a real argument for buying major-brand automotive two post lifts new rather than gambling on cheap imports that can’t be rebuilt cost-effectively.
Step Four: Prepare for the Rebuild Job
A cylinder rebuild on a two-post lift isn’t hard if you’ve done any hydraulic work before, but it does require space, clean tools, and about four hours per cylinder for a first-timer. You’ll need to fully lower the lift, disconnect the hydraulic hoses, unbolt the cylinder from the carriage and column base, and get it to a clean bench. From there it’s disassembly, seal replacement, cleaning of the bore and rod, and reassembly with fresh hydraulic fluid. For a restorer used to engine work, the process is familiar. The main thing is cleanliness — any dirt in the reassembled cylinder shortens the new seal life dramatically.
If you’re not sure about doing the rebuild yourself, we send cylinders out to a local hydraulic shop and get them back in about a week. That option runs $175 to $250 per cylinder including seals, still well under a full cylinder replacement. The southwest Iowa restorer did his own rebuilds on his kitchen bench after a shop-vac cleanup, and both cylinders have held pressure for the six months since we last checked in. He was proud of the work and rightfully so.
Step Five: Flush the Full System After Rebuild
New seals go into fluid that’s been running in an old system, and that old fluid has picked up microscopic metal, rubber crumbs, and water. Reassembling clean cylinders and then plumbing them back into dirty fluid shortens the new seal life significantly. Any cylinder rebuild should be followed by a full fluid drain, filter replacement if the lift has an inline filter, and a fresh fill with the manufacturer-specified hydraulic oil. On Rotary and Challenger automotive two post lifts, that’s typically an ISO VG 32 or 46 anti-wear hydraulic fluid depending on the model.
Flushing also means cycling the lift multiple times without load right after rebuild to work air out of the system and confirm smooth motion. Any hesitation, jerking, or unusual noise during those first cycles points to trapped air or a reassembly issue. Fix it before you raise a vehicle. The southwest Iowa lift needed about eight cycles to fully bleed, and once bled, the drift issue was gone. His welding sessions on the C10 now run four hours with the lift not moving a millimeter.
When Rebuild Isn’t the Answer
Some cylinders are past rebuild. If the bore is scored, the rod is bent, or the barrel welds are cracked, no seal kit will save it. In those cases, the honest answer is a complete cylinder replacement, which on major-brand lifts is available as an OEM part. On unsupported imports, the answer is sometimes a whole new lift. That’s a hard truth for someone who bought a used lift cheap, but it’s better to hear it before spending three weekends on a rebuild that won’t hold. We diagnose this over the phone with photos when a customer isn’t sure.
For anyone weighing a used automotive two post lifts purchase against a new one, factor the possible rebuild cost into your used-lift math. A $2,000 auction lift plus $200 in seals plus your Saturday afternoons still probably beats a $5,000 new lift on total dollars — but a $2,000 auction lift plus $2,000 in new cylinders and hoses does not. Diagnose before you commit. That’s the whole point of this checklist.
Keep the Cylinders Alive Long Term
Post-rebuild, the biggest lifespan-extending habit is annual fluid checks. Pull the reservoir cap, look at the fluid color, check the level, and replace anything questionable. Water contamination is the number-one killer of hydraulic seals in unheated Iowa shops, and catching it early saves the whole system. Second habit: exercise the lift regularly. A cylinder that sits for months at a time develops flat spots on its seals from static compression. Running the lift full stroke once a week even without a vehicle keeps the seals moving and the fluid circulated.
If you want a checklist for maintaining your rebuilt cylinders that you can post in the shop, we’ll send you one — it’s the same one we give every restoration customer. Call 800-674-9302 and we’ll email you the PDF along with a parts sheet for your specific lift model. The goal is a rebuild that lasts another 15 years, and with the right habits, that’s a completely realistic outcome.
Our Clients Include: