Brompton刹车线固定装置 - 从四速到五速转换

Brompton brake cable holder - 4 to 5 speed conversion

2023-08-18 20:38:39

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Summary

A quick fix to solve the “rubbing brake cable housing on chain – issue” of Brompton P-Lines if upgraded to 5 speeds or more.
The new P-Lines can easily be upgraded from 4 to 5 speeds without changing the freehub body whatsoever. All you need are the first 5 cogs of a Shimano DEORE CS-M5100 11-speed cassette, 11t-13t-15t-18t-21t and the corresponding spacers (with some effort you also can find the parts separately which usually comes cheaper https://si.shimano.com/de/pdfs/ev/CS-M5100-4665/EV-CS-M5100-4665A.pdf). Since the original Brompton cassette is based on a 9-speed spacing, the narrower 11-speed cogs will fit onto the freehub but you also have to remove the original plastic disc spacer right next to the spokes. The only tweaking is, that you have to file down 6 teeth of the 21t cog. On three spots on the cog two neighbored teeth are slightly higher than the others and those will otherwise collide with the nut of the shifting cable clamp on the derailleur while the chain is on the 21t cog. Just take 1 mm off each of those teeth, deburr it and you’re good. It doesn’t affect the shifting quality at all. I also changed the M5 locknut of the derailleur cable clamp for a regular M5 nut since it’s shallower and filed the bolt a tad shorter. Last thing you need to make it work is a 11-speed SRAM MTB shifter (Shimano won’t work due to different incrementation). A GX-model works fine, the XX1 are lighter and the indexing feedback is a bit sharper. I combined this setup with 54t narrow-wide chainring which makes the chain catcher obsolete. Lastly, you’ll need a new chain since the original one is 10-speed and won’t fit. I prefer to run 12s chains like the CN-M7100 on 11s setups. They have the same inner width than 11s ones but the outer width is 0.25mm slimmer which gains more space between the chain and the neighbored cog and therefore runs quieter.
Now back to the printed part. Since you added an extra cog on the left of your cassette, the chain line on this particular cog will run further left as well – and might scrub on your rear brake cable housing. The cable holder is heavily inspired form the one Union Jack offers and does the same thing. Print it, route your cable through the holder and clamp the two parts with an additional M4x10mm countersunk screw onto this little welded-on tube on your seatstay. Done.
Disclaimer: Only run a 21t cog as largest sprocket, larger ones will smash into your derailleur. Depending on how your derailleur is mounted there’s a chance, that the 21t teeth might touch the teeth of the derailleur pulley while shifting from the 18t to the 21t cog. But that’s an easy fix. Just loosen the two derailleur mounting bolts and turn your derailleur slightly counter clockwise while you’re tightening the bolts again. There’s little wiggle room in the fit of the derailleur and this method generates just enough clearance to make shifts run smoothly. Enjoy your ride!
-bikenerd