Seat post clamps work by compressing the bike's frame around the seat post. When you push the lever on the clamp, it locks the seat post into place at your desired height. With a flick of the lever, the clamp is supposed to release the seat post. Occasionally it strips, won't hold the seat in place or locks up. You can change out that old seat post clamp and be back on the road again in about 15 minutes.
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Wrap a piece of tape around the seat post where the seat post meets the bike's frame tube. This is for height reference when you put the seat back on.
Hold the knob on one side of the lever with your fingers. With your other hand, spin the lever counterclockwise until it comes loose. Pull the nut off with one hand. Pull the lever off with the other hand. Grab the bike seat with both hands. Twist the seat back and forth as you pull it straight up and out of the frame tube.
Hold a small block of wood on the bike's frame underneath the clamp, making contact with the bottom of the clamp. Tap up on the block with the hammer to dislodge the clamp from the frame. When it comes loose, move the block around the perimeter of the clamp, tapping it up evenly until it pops free of the frame tube.
Unscrew the new clamp as far as it will go without dropping the nut off the end of the lever. Place it on the tube where the old clamp came off. Place the block of wood on top the clamp. Tap down on the block, forcing the clamp down the tube. When the block makes contact with the frame, stop tapping.
Insert the seat post back into the frame tube to the point where you marked it with tape. Twist the clamp lever four turns and try to close the lever with your fingers. If it is too tight, twist the lever counterclockwise one turn and try again until the lever closes snugly. If it is too loose, and the seat post is not tight, twist the lever one turn at a time clockwise and test until the lever closes securely and the seat will support your weight without moving.
Tips and warnings
- Ride the bike for a few days and check the seat post again. Often, it loosens up a bit when getting broken in.
- Other seat post clamps do not have a lever and are tightened by a hex nut. Technically these are called "binders" instead of seat post clamps. They change out the same way as the lever clamp, but you need a 5mm hex wrench to loosen the nut and then remove the clamp.
- Don't over-tighten the clamp and break it. If it starts to bend, it's too tight. Loosen by twisting the lever counterclockwise and try again to close the lever.