Tight Bushings

Missing Link kits manufactured in the spring of 2025 come with a new and improved bushing design and tolerances that eliminate this issue.

However, during some rebuilds (with Missing Link kits manufactured in 2024), the bushings can sometimes fit too tight, preventing the links from moving freely. A very small amount of friction is OK, but the links should not have too much friction for the servo or return spring to move the links easily.

Ideally, the bushings should be a very light press fit into the links, and the pins should rotate freely inside the bushings. 

The tolerances of several parts need to match up just right to take the slop out of the linkage, yet still rotate. Because of this, if a few factors conspire in the wrong way, they can be too tight. 

What Causes This?

  1. Variation in the outside and inside diameters of the bushings. The outside and inside diameter are each within ± 0.02mm.
  2. Variation in the diameter of pins. They are within ± 0.01mm.
  3. Variation in the diameter of the holes in the links. They are within ± 0.02mm.
  4. Variation in humidity. This can affect the bushing size significantly. We use Delrin (POM) material for the bushings. Even though it has relatively low moisture absorption (compared to other polymers), normal ambient humidity variation affects the precision fit diameters enough to matter. We've been monitoring this issue for more than a year in different regions, and it is predicable with the seasonal humidity fluctuation, changing the diameters by as much as 0.02mm.
  5. Sometimes, a lot of compression is needed force to install the pins with the press tools. This can deform the bushings during the pressing process, reducing their inside diameter, which squeezes the pins.

Options

This video shows these options.

  1. Use loose fitting bushings. We have 2 types of bushing fit: The standard fit and a "loose" fit. If the standard ones are too tight, try the loose fitting ones. 
  2. Use the Madrone pins. The Madrone pins fit better than the SRAM pins. If the SRAM pins are too tight, try the Madrone pins. Check the pin fit on the bushings right after you slide bushings into the links, and before they go on the derailleur. This way you can change anything easily before you get further.
  3. Ream the bushings. You can increase the ID of the bushings. Use a drill bit that is just a little smaller than the ID of the bushings. This sounds risky, but if you use a drill bit that is smaller, it works well. For example, for the 5mm bushing, you can use a 3/16" (4.8mm) drill bit. Or for the 4mm hole, you can use a 1/8" (3.2mm) drill bit. How? With the bushing pressed into the link, spin the drill bit with a drill to gently shave material off the ID of the bushing. With the drill bit spinning, move it in circular motion to evenly take material off all areas of the inside of the bushing. When doing this, make sure to check the the fit frequently to make sure you don't remove too much material from the inside of the bushings.

Other Options

  1. Reduce the OD of the pins. Use a drill and fine grit sandpaper, followed by an abrasive pad to get a smooth surface finish. Chuck the pin in a drill, and spin it while using the sandpaper to remove material from the bushing surface. During this process, check the the fit frequently to make sure you don't remove too much material from the diameter of the pins.
  2. Use a lubricant, but carefully. In general, we do not recommend using a lubricant because it can attract grit and ultimately wear the bushings faster. However, a small amount of grease or wax chain lubricant can help. Make sure to wipe off all of the excess.