The Shimano friction clutch mechanism built into modern rear mech's is designed to eliminate chain slap and also keeps the chain under tension between the cage and the cassette. It works by using a one way friction place that keeps the chain taught and consistently under tension, it allows a small amount of movement for chain growth but pretty much eliminates the chain pulling on the rear cage over rough terrain, ultimately improving gear change too. It is in my opinion a great step forward and one of the best creations in cycling, I have ridden with it extensively and it does exactly what it says on the tin. Now the drive chain is that much quieter you can actually pick up on other noise from your bike, tyre resistance, motor noise etc. Although initially it was only featured on Shimano's top end rear mech's it has worked its way down the grape vine and the technology is now available on lower spec rear mech's (Shimano SLX for example). This in turn means that it is now featured on many mid - top end eBikes. Mainly of the MTB genre. Although it has been around for a few years now, I still get asked about it on a regular basis so I though I would do a little write up on it, to give users a little info on how it works and how it is maintained.If you have bought a eBike in the last couple of years and the drive chain is SLX level or above you probably have this technology on your eBike. It will have an on and off switch as follows.
The switch is here only to allow you to be able to remove the rear wheel easily from the frame, as the mech is difficult to move when the clutch is engaged its a real nice touch to be able to turn it off. It is clearly marked on and off and there is an easy lever to operate each way.Now many eBikes will be shipped out with the clutch in the off position so make sure it is turned back on prior to riding. This switch also makes it easy to see what a difference the clutch makes. For example go for a ride with it turned off, then mid ride turn it back on and you can feel/hear the difference straight away!Anyway, enough about how it works, I bet a lot of you reading this are thinking.. "Its just one more thing to go wrong!". Well I have been dealing with these in the workshop for a few years now and although Shimano offer spare parts for all their rear mech's including the clutch mechanism it self I am yet to actually replace parts here. Seeing as the rear mech takes such a beating on the trail and it such a vital part of the drivetrain I think its really durable for what it is. Over extended use the clutch mechanism can fade slightly but it can actually be adjusted by the end user, its fairly easy to do as well on the newer ones. There are probably many how to guides for how to adjust it with a quick google search. But the gist of it is, you remove the plastic cover with 3 allen bolts, the clutch itself can be adjusted using an allen key, its simple to adjust the tension, turn it clockwise for more tension and counter clockwise for less tension. But don't crank it right up, just make quarter turn increments at a time, until the tension is set. (This is how to adjust the SLX and XT models, the XTR is slightly more tricky, google it!)Anyway enough of my babbling now, many of you probably already know all of this, but for those who don't, by me spending ten minutes to write this up will probably save me that triple amount of time on the phone..When I get the call 'What's the switch all about on my rear mech?'.. Maybe I should say, switch it on - and your eBike will float over water!View Electric Bikes that come with this Mechanism