As the Ramblas is our first bike with a cable-actuated dropper post, this may be the first time some of our customers (or shops) have dealt with or troubleshot a dropper post. As used dropper posts can have many more reasons they may not be functioning properly, a new bike will generally have dropper issues narrowed down to the cable and housing.
The main reasons the dropper may not work on a new bike:
- Cable housing unseated, obstructed, or pulled on.
- Cable is improperly adjusted (too little or too much cable tension)
- Visible damage to cable housing or cable. (not common)
Vocab:
Cable: It is silver and metal, The actual cable that performs the function (inside the housing)
Cable Housing: Outer protective channeling for the cable to move. Consists of a nylon center, wrapped in steel and black polymer outer later.
Housing end or Ferrule: Plastic ends that are installed on the end of the cable housing when it is cut to length which creates a clean and sealed end. (shifter/ derailleur setups will commonly use the same size cable housing and ferrules as droppers.
What is a dropper post?
How a dropper post works
The dropper post functions using a thumb lever on the left side of the handlebar. When the lever is pressed, it pulls the cable which runs through the bike frame and is attached to a lever at the bottom of the seat post. When the cable is pulled, the internal valve of the seat post opens allowing the internal pressure to raise the seat to full extension. When the lever is released, the cable retracts and the seat post locks in place, holding the rider's weight. To lower the seat post, the rider will sit on the seat while pressing the thumb lever and their weight will push the seat down. Once the seat is down, the rider can release the thumb lever and the seat will remain down until the thumb lever is pressed again.
Below, the diagram shows how the internal cable is routed in the bike for the dropper post. (Dropper cable/ housing represented in red.)
Cable Bushings:
An internal dropper post engages the seat post using a cable bushing to fit into the lever on the bottom of the seat post. (as shown below) Most droppers can utilize a standard shift cable paired with the appropriate cable bushing in order to function the dropper. The cable and housing are commonly stocked items in most bike shops as they are universal so the only proprietary part for the dropper would be the bushing itself.
The Ramblas uses a KS dropper post and the early versions included a specialty dropper cable with the shape of a cable bushing permanently attached to the cable end. If the cable needed to be replaced, a standard shift cable would not be sufficient unless the mechanic sourced the appropriate cable busing compatible for this post. We however have two current options to provide a solution.
Option 1: We have a SKU in stock for Ramblas dropper cables that have the special end attached Aventon Seatpost Cable Ramblas SKU: 19005-7000050 Option 2: The shop/ customer will need to get a standard universal shift/ dropper cable and then purchase on of these cable bushings online (google: "dropper cable bushing") and two common results of bushings will populate. KS droppers (like ours) will use the set screw style "Style 1" and other brands like FOX or One Up will use the "Style 2" bushing.
Style 1 Bushing (compatible) Style 2 Bushing (not compatible)
Style 1 bushing is installed by sliding the cable through the center hole (Figure A) all the way till the cable end reaches the bushing and leave a few mm of cable from the end (Figure B) and tighten the set screw till snug to lock the bushing to the cable. Use some flush-cut cable snips to cut off the original cable end (Figure C/D) and now the cable can be used in the dropper (Figure E).
Figure A Figure B
Figure C/D
Figure E
Option 3: (Shown below) is the newer style of cable bushing attached to a standard shift/ dropper cable. The shape is similar to the Style 1 bushing so it will fit with the seat post but this kind does not have a set screw, similar to the Style 2 bushing. If the bike is equipped with this style and needs a cable replacement, simply remove the cable from the bike. Slide the bushing off of the old cable and transfer it onto the new cable. Now the new cable is able to be used on the dropper. Reinstall the cable and adjust accordingly. Currently, this newer style of bushing does not have its own part number so it will only be available if it originally came with the bike.
Troubleshooting
- Cable housing unseated, obstructed, or pulled on.
The dropper post setup uses a cable and housing to actuate. Both ends of the housing must be properly seated to allow the lever to pull the cable, effectively actuating the seat post. The housing can be accidentally pulled when assembling the bike or if the bars are turned too far in one direction. Sometimes this will pull the housing enough to dislodge it from its proper position and the housing may "hang up" on the outer edge of where it should be seated. If this happens, the cable is effectively being pulled and the lever will feel stuck. This issue can happen up at the lever end (figure 1) OR down inside the frame at the bottom of the post. (figure 2). To correct this, pull and reset the housing into the proper place as shown in (figure 3) for the lever and (figure 4) for the bottom of the post. You can also try feeding some excess cable housing into the top of the bike and retest if the dropper lever now functions. If the issue still persists, we will need to access the seat post.
Figure 1 Figure 2
Figure 3 Figure 4
To access the bottom of the seat post, use a Torx T25 to remove the bolt holding the dropper lever to the front brake lever clamp (figure 5)
Figure 5
Once removed, the lever and cable housing are on their own. Next, loosen the seat post clamp bolt (figure 6).
Figure 6
Now push cable housing into the bike on the lever end while pulling up on the seat post. Pull up until the bottom of the seat post is exposed. (figure 7)
Figure 7
Once the post is lifted up, ensure the lower cable housing is properly seated in its groove. While the seat post is out, you can also test the system (with the help of another person) to make sure the seat post now works properly by depressing the lever. Once the function is confirmed, carefully guide the seat post back into the frame while simultaneously pulling the housing forward out of the front of the bike. (This is where many may cause an issue and unseat the housing on the bottom of the dropper). When reinstalling the post, the trick is to not pull more cable out the front than you are displacing by pushing the seat post into the bike. Hold the thumb lever down while pulling the cable through the bike as this will keep tension on the cable, allowing the cable housing ends to stay properly seated. Once the dropper post is positioned at its desired height in the frame, tighten the seat post clamp and reattach the dropper lever to the handlebar. Once again test the function to ensure the post raises and lowers properly.
(Note: While the post is being accessed, the post can also be tested independently by lifting the cable end out of the bottom of the post, therefore freeing the post. Then, with the post upside down, press the bottom lever arm on the post and press the saddle into the ground, depressing the seat. Test the extension of the dropper post by pressing the lever on the bottom of the post with your fingers. This test will verify that the post itself DOES function and that the issue resides with the cable or housing placement or adjustment.)
- Cable is improperly adjusted (too little or too much cable tension)
Another symptom of a cable issue is that the lever moves but either the cable does not have enough tension or has too much tension. If the cable has too little tension, the post will either require a very deep press of the thumb lever to function, or it will struggle to even extend as the lever is not displacing enough cable slack to actuate the post. To increase cable tension, unthread the barrel adjuster out from the dropper lever turning it counter-clockwise (figure 8). This will effectively pull the housing back in small increments, increasing cable tension. (Note: the barrel adjuster can completely unthread if turned too far. If that much slack is present, thread the barrel adjuster back into the lever and proceed to the next step. For larger amounts of cable slack, it is best to loosen the cable pinch bolt on the lever, pull the excess cable slack through the lever, and re-tighten the pinch bolt in place (figure 9). From there retest the seat post function and use the barrel adjuster to make fine adjustments. If the cable has too much tension, the seat post may never "lock out" and may allow for movement when the lever is not being depressed by your thumb. Another sign of too much tension is if the seat post slowly slides down when the rider's weight is on the saddle. To correct this, turn the barrel adjuster clockwise, threading it into the lever, which shortens the overall length, releasing some cable tension. If the barrel adjuster does not provide enough slack, loosen the cable pinch bolt to release a more significant amount of tension. Usually allowing the cable to release on its own is sufficient. Retighten the pinch bolt and make fine adjustments with the barrel adjuster.
Figure 8
Figure 9
- Visible damage to cable housing or cable.
If the dropper cable and housing are inspected and there is visible damage like fraying or sliced housing, this is an indication that the damaged parts should be replaced. A kink in the cable housing can usually be bent back to reopen the internal channel and does not always need to be replaced. If the cable and housing need to be swapped out, this video shows the process from start to finish.