The small vertical shaft at the base of each swing arm on a 2-post lift is one of the most safety-critical parts on the machine. It does two jobs at once: it lets the arm rotate to reach the vehicle’s lift point, and it locks the arm in place under load so it cannot swing sideways while the car is in the air. That part is the lift arm pin, sometimes called the arm restraint pin or the arm-lock gear pin. This guide covers what it does, how to spot a worn one, and how to identify the correct replacement for your specific lift.
What the lift arm pin actually does
Every 2-post lift arm rotates on a vertical shaft that passes through the carriage’s arm boss. Splined onto that shaft is a gear (sometimes a toothed disc, sometimes a serrated collar) that engages with a spring-loaded pawl or locking pin. When the arm is at rest, gravity and geometry keep the gear disengaged and the arm can swing freely. As soon as the lift raises the vehicle off the ground, the arm-restraint mechanism engages the gear teeth and prevents the arm from rotating.
If that gear or the pin passing through it wears, the teeth stop biting cleanly. The arm can then creep or, in the worst case, rotate suddenly under load. Because the vehicle’s whole weight is on those four arms, a slipped arm can drop a car in a heartbeat.
Model-specific parts, not universal
There is no universal replacement. Each manufacturer has its own arm-lock geometry, spline count, shaft diameter, and gear-tooth pitch. On a Rotary SPOA10 or SPO series, the pin most techs are looking for is Rotary part S130105 (and its companion gear and pawl); on newer Rotary lifts the assembly changed and cross-references matter. Challenger 2-post lifts use their own family of arm-restraint pins with different spline counts and lengths depending on model and year.
You cannot substitute across brands. Even between two lifts from the same manufacturer built five years apart, the lift arm pin assembly can be completely different. Always identify by model and serial before ordering.
Wear indicators to watch for
The first sign is almost always a subtle one: an arm that used to click firmly into place now feels vague, or the arm slowly creeps a few degrees when a vehicle is loaded on it. That is worn gear teeth on the top of the pin assembly, not a bent arm. Other symptoms include:
Visibly rounded or missing gear teeth when the arm boot is pulled back. A rattle from the arm base when the arm is unloaded. Metal shavings or brass-colored dust around the arm pivot. A locking pawl that no longer springs back cleanly. Arms that swing under load. Any of those, and the lift comes out of service until the lift arm pin is replaced.
Inspection procedure
With the lift down and unloaded, pull the rubber boot at the base of each arm up the shaft to expose the gear teeth. Wipe the grease off with a rag. Compare the teeth to a photo of a new assembly, or to the teeth on a different arm on the same lift that has seen less use. Rounded, chipped, or missing teeth mean replacement. While you are in there, check the shaft for scoring, the retaining pin or C-clip for cracks, and the pawl for spring tension.
If you are unsure, do not gamble. Send us photos of the exposed gear and we will tell you whether it is serviceable.
Replacement effort
Replacing a lift arm pin is more involved than most single-part jobs on a lift. The arm has to come off the carriage, which usually means unloading and safely supporting it (arms are heavy and awkward). Then the retaining hardware at the top of the pin comes off, the pin drops out the bottom, and the new pin and gear go back in. The pawl or spring assembly typically gets replaced at the same time.
A tech who has done it before can turn one arm in an hour or two. A first-timer will spend most of a day per side. Bundling all four arms into one service visit is the efficient play, because you already have the tools out and the lift down.
Ordering the correct pin
For Rotary 2-post lifts, our Rotary aftermarket parts collection carries the common arm-restraint pin assemblies and matching gears. For Challenger, the equivalent parts live under Challenger aftermarket parts. For every other brand or an older lift where the badge is long gone, the parts lookup tool is the fastest way to translate a serial number into a shipping part.
What we need from you: the lift manufacturer, the exact model number, the serial number if you can find it, and a photo of the current pin and gear if the tag is missing. With that we can pull the correct lift arm pin off the shelf and get it moving the same day in most cases.
Related wear items
When we replace an arm-restraint pin, we plan to also replace the pawl or locking pin, the gear itself (they wear as a set), the arm boot if it is torn, and the arm-pivot grease if it is dry. Doing all of that in one visit gets the arm mechanism back to like-new engagement.
When to just call us in
If your shop does not have the manual, the correct hardware, or a lift for the tech to stand on while wrestling with heavy arms, this is a job worth farming out. Our field service crew replaces lift arm pin assemblies on a routine basis and can bundle it with a rope inspection, cylinder reseal, or safety check in the same visit.
Send us the make, model, and serial of your 2-post lift and we will identify the correct lift arm pin kit, quote it, and get it shipped or installed. Start with our parts lookup tool or call us at 800-674-9302.
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