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The chain stabilizer (blue in the sketch below; source) consists of two parts.

chain stabilizer

The two parts are:

  1. an outer metal part (top right of the image below), and
  2. an inner part (bottom left of the image below).

parts of the chain stabilizer

In this video Truman shows the inner part and stresses that its outer cyclindrical surface should be lubricated (by a high-performance grease, because under use the friction can generate heat as high as 450F), but that the flat top should not be lubricated—as the instructions on Shimano's site also say.

It is evident from the video that the inner part is itself made from two materials.

Despite sharing the same name, this is quite distinct from the clutch in cars with manual transmission. How does it work? (Why does it rotate with less—or no—friction clockwise, but resists movement when rotated counterclockwise?)

Ideally you've used up one such part and were too curious not to break it apart and look inside, in which case it would be perfect if you can share with us what you saw.

Related

The present question is a sequel to this question. That question asks how an RD clutch works from the outside (how it is used). The present question asks how it works on the inside.

History

The earliest this tech was described is April 25, 2011 (that I've found).

1 Answer 1

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The core of this inner part is made from metal. It has eight protruding teeth.

The teeth engage in a rubber or rubber-like material.

The rubber-like material in turn is wrapped in a thin cylindrical ring.

The trick is the asymmetry of the protruding teeth. When rotated clockwise they use friction to turn the rubber-like material. Hence no grease can enter the surface between the protruding teeth and the rubber-like material, for otherwise the core could slip and jam the clutch.

When rotated counterclockwise, the protruding teeth exert an outward pressure on the rubber-like material. That outward pressure in turn pushes the cylindrical ring, which then has more contact with the adjustable ring, leading to a slower motion despite the presence of grease.

Under counterclockwise rotation the presence of grease at the undesirable interface would also be problematic. If the protruding teeth slip, they could again jam the rubber-like material.

This answer is speculative. Please critique or correct. In particular, this answer does not explain why there are four separate sections to the core of the chain stabilizer.

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  • If you're referring to the three circumferential grooves by "four separate sections", those are most likely for grease retention. Pretty standard feature on plain bearings like that.
    – MaplePanda
    Feb 8, 2023 at 20:20
  • @MaplePanda That makes a lot of sense. It would also suggest that the plastic (black) part might be made from a single piece.
    – Sam7919
    Feb 8, 2023 at 21:04
  • So it’s not a normal ratchet and pawl mechanism? I kind of had expected it to be free wheeling in one direction and (after a pawl engages) working against friction (exerted by the metal band) in the other.
    – Michael
    Feb 9, 2023 at 9:48
  • @Michael Good point. Not only can an RD clutch be built based on a ratchet, but that's how Microshift does it (RD-M6195L). But Shimano doesn't use a ratchet. You can see here youtu.be/0j7p1DP2R5Y?t=735 that they're not pawls. Also, if Shimano did use a ratchet, without removing the cover we'd hear the clicking sound as the arm returns. They're likely dodging each other's IPs (and patents). I'm curious how SRAM does it. The SRAM clutch release button suggests it's yet a distinct system.
    – Sam7919
    Feb 9, 2023 at 16:40

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