Clutch maintenance

September 17, 2022 § 3 Comments

No, not on one of our manual transmission automobiles.

Modern mountain bike derailleurs (rear, of course; there are no front ones anymore*) have a clutch mechanism. It’s designed to minimize bouncing forces which can extend a clutchless derailleur, which can cause chains to slap up against the seat stay, and to disengage the chainring.

When I got my new 1×12 drivetrain I just assumed this was necessary and left it on.

I’ve have experienced slowed shifting over the past half year or so. Not particularly annoying at first, and I figured the usual, cable stretch. Maybe combined with a little bit of chain wear that was letting it drift a little from side to side. At around 666 miles and 6 months I put on a new chain and it did seem to slightly refresh the shifting. Somewhere around a year and 1,200 miles in, I bought a chain wear indicator and started checking. The second chain has been marginal, but is still measuring within 0.5% elongation, the recommendation for 12 speed Shimano chains.

Aha. Time for some maintenance. For reference, Strava claims 1,523 miles on the bike so far. The online videos were super helpful and more or less assured me that the issue was unlikely to be dirt contamination and much more likely to be grease related. Taking it apart was really easy.

Since my direct replacement chain runs $46 and availability is still iffy, I’m keen to stick to the data instead of my seat of the pants and eyeball method. I’m also keen to replace chains when needed because a worn chain is notoriously hard on cassettes. The direct replacement cassette for my bike costs $165 or, approximately 3.5 chains.

For some reason I recently thought to switch off the derailleur clutch to see if shifting was improved and IT WAS! Like, by a LOT! Duh?

Dis-assembled clutch

I heard one claim that the clutch gets really hot. Not sure if I believe that but it was in the vein of telling me I needed a high temperature grease. For this first try I used the regular old bike grease that I use for everything. In terms of visual inspection, it was very much the case that the seal kept out the dirt but that the clutch mechanism had no grease left.

I greased the clutch as described in the videos, and put it back together. There was one little hiccup trying to get the cover back on. I resolved this by placing the clutch part and the tensioner part on separately, checking the cover fit, and then duplicating that when putting the two mechanism back on at the same time.

The clutch action was much smoother with the hand test, so mission accomplished. I messed around a little bit with the tension adjuster to make sure I had a feel for how much of a turn should result in a change in tension.

I was unable to set the tension by torque wrench (I gather 3-5 nM is the range) because my cheapie bike torque wrench only goes in the tighten direction and I don’t have the right attachments for my motorcycle one (yeah I’m not leaving motorcycle bolts to the “educated hand” strategy thank yew).

I did three or four rides with the clutch disengaged before this and did not notice any chain slap noise OR experience any derailment from the chainring. So I may not need a clutch at all, and if I use it can probably get away with very light tension.

The clutch in situ

I will be very curious to see how my grease job holds up over the next year. Not sure I totally buy the temperature thing but it was bone dry, so clearly the grease on the clutch mechanism takes a beating.

I decided to replace the chain. Although the gauge is still reading only close to 0.5% wear, and has been for the last 300 miles, my cassette cogs are showing some wear. I was a little surprised at how much, when I looked at the cogs with some focus. And this is the kind of wear that happens with a worn chain. Classic signs. New chain time. Interestingly there is no stamping on the quick-link to indicate the installation direction. And the Shimano stamped side plates appear to be randomly assembled. I think there is some possibility this eBay sourced chain may have someone dodgy provenance.

So now I’m on cog watch. And anticipating that in about 600 to 800 miles I may need to do both chain and cassette and probably even the chainring for good measure.

I tuned up the front brake, which has been rubbing ever since I replaced the pads. I had been waiting to get a bit of initial wear but it was not enough. It turns out that rotor was slightly warped, so I broke out the highly sophisticated rotor truing tool- a Crescent wrench. These work great to gently bend a rotor back into true. Then I could get the brake caliper in the right place.

I checked on the dropper actuator and it was far from coming apart, but definitely unscrewed a bit. Still something to keep an eye on.

The pink Muc-off tire sealant was no longer liquid and pooling. There was a thin skin of damp sealant all along the center tread but that was it. I topped that off with about 2 oz per tire. Interestingly I have not heard any leaks being sealed with this sealant on board or noticed any pink latex. Two and a half months seems short but then again we’ve had four weeks of a heatwave. For now I’m chalking it up to the heat.

Update: The shifting is much improved on the first ride, with the clutch back on.


§ 3 Responses to Clutch maintenance

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