Suspension seat posts seem to be one of those things that people ignore – perhaps because they come fitted to new bikes rather than having been specifically chosen, or perhaps because their performance deteriorates so slowly that you don’t really notice until the moment when they actually stop working completely.
The most common problem is that the knurled nut that holds the two parts of the post together has a tendency to work itself slowly loose. The spring that’s trapped between the two parts then finds itself with plenty of elbow room. When this happens, the spring isn’t compressed at all by your weight and just rests at the bottom of its travel without supporting you in any useful way at all. If the knurled nut continues to work itself loose, the top part of the post can become completely detached from the bottom part.
Normally they don’t separate of their own accord, because the top part rests inside the bottom part, but if your bike falls over or you bump off a deep kerb, they will soon part company. You do get some warning when this starts to happen – instead of absorbing bumps smoothly as you ride, the post will sink slowly to the bottom of its travel, resting at its lowest point. You’ll start to feel every bump you ride over, and you may even feel the post knocking as you go round tight corners.
The other problem that can occur is that the interface between the two telescoping parts of the post can corrode, so that they don’t slide easily over each other and, however strong the spring is, the post won’t respond to bumps. It doesn’t happen all of a sudden. There will be a period when the movement of the post starts to feel lumpy and the saddle shifts in discrete jerks rather than with a smooth flow. If you catch it at this stage, there’s hope as you can give the post a new lease of life by taking it apart, cleaning it and re-greasing it. The steps below show you how to do this. If you leave it much longer, the spring will become embedded in the post. The simplest and cheapest solution at that point is usually to replace the post.
It’s worth getting the post out of the frame regularly and re-greasing the outside of the post as well as the inside of the frame. You don’t need to use anything particularly fancy; ordinary bike grease will do the job just fine. If you don’t do this and simply leave the post in the same place for years at a time, it will end up stuck (seized) within the frame. Parking your bike outside frequently will mean it’s exposed to the weather, which will greatly increase the speed of corrosion.
A seized seat post is not an immediate problem as long as you never want to change its height, but you won’t be able to access the bottom of the post to adjust the spring preload. Moreover, you’ll be stuck if you ever want to lend the bike to someone who’s a different height, or to sell it.
Step 1: Ensure that the knurled nut at the top of the bottom section of the post is screwed down securely. These often work loose without anyone noticing. You’ll have to lift the black rubber boot up and out of the way to turn the knurled nut. Keep turning the nut – if you stand over the saddle the nut must turn clockwise although you won’t actually be able to see it because the saddle will be in the way.
Step 2: Remove the seat post from the frame. There’s a cap on the bottom of the post. Note how deeply the cap is recessed and then use an Allen key to remove the cap. The spring will drop out. Clean it since it will be greasy and sticky. Once it’s clean, spread a generous dollop of fresh grease all over it as the sides of the spring rub inside the post and need lubrication. Replace the end-cap, taking care that it goes in square, not cross-threaded.
Step 3: Tighten in the end-cap so it’s as deeply recessed into the frame as before you removed it. The end of the cap must not protrude beyond the end of the post. Clean the outside of the post and the inside of the frame, then smear grease on the outside of the post. Refit the post. Insert it far enough into the frame so the ‘min insertion’ marks – a band of short parallel lines – disappear. If your saddle is too low, the seat post is too short and should be replaced.
Source : BIKE MAINTENANCE TIPS, TRICKS & TECHNIQUES
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