Dropper Seatpost Replacement Cartridge

Match it to the post you already have. Internal 125mm and Internal 150mm are for the internally routed UpDown dropper in its two travel options; External 70mm and External 125mm are for the externally routed version. The travel figure has to match what the post is now — a 150mm cartridge will not turn a 125mm post into a 150mm one, because the post body is built around its own travel.

Internal or external is the easy half — look at where the cable leaves the post. An internally routed post takes the cable in at the bottom and it disappears into the frame; an external one has the cable running down the outside. For travel, drop the post fully, raise it fully, and measure how far the stanchion moves between the two; that number is your travel and it will be close to one of the figures listed here. The model or SKU printed on the post will confirm it.

Not necessarily, and it is worth trying the free thing first. The UpDown uses an RCR cartridge, which was designed so the rider can reset the hydraulic circuit rather than send the post away — a good deal of squish, sag and slow return is simply air in the wrong place, and the reset procedure in the post's manual clears it. If you have reset it properly and the post still sinks under your weight or will not hold full extension, then the cartridge itself has had enough and this is the part that replaces it.

That is exactly why this is still on the shelf. The post is no longer in production, but the cartridge is the part that wears out — the stanchion, collar, bushings and lever hardware all outlast the hydraulics comfortably. Keeping cartridges available means a post that is otherwise in good order does not get thrown away over one component, which was the thinking behind making the cartridge replaceable in the first place.

It is a home-workshop job rather than a shop-only one — basic tools, nothing proprietary to buy and nothing to press in. The post comes apart, the old cartridge comes out, the new one goes in. Work through the instructions for your post rather than from memory, and pay particular attention to how the cable actuation is set at the end, because that is what decides whether the lever feel comes back the way it should.

No. These are built around the Funn UpDown and nothing else. Dropper cartridges are specific to the post they were designed for — diameter, length and the way the cartridge is actuated all differ from brand to brand — so there is no cross-brand substitution here even where the travel figure happens to be the same.