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-   -   changing rear cable: shifters=RapidFire Plus, derailleur=low-normal/Rapid Rise (

TomRoche 02-25-15 08:22 PM

changing rear cable: shifters=RapidFire Plus, derailleur=low-normal/Rapid Rise
I recently broke the rear-derailleur cable on a bike with
  • rear shifter: a non-Shimano RapidFire Plus knockoff from an LBS parts bin
  • rear derailleur: Shimano Nexave, a fairly generic indexed low-normal (aka "Rapid Rise" (i.e., spring pulls chain to biggest sprocket) rear derailleur
  • cable, housing: Jagwire L3

I realize lotsa folks hate low-normal, but I was grateful for it, since my cable broke in mid-ride :-( It also broke at the shifter end (inside the shifter, at the point on the cable where it attaches to the cap), but that's quite usual in my experience. I looked online for instructions about how to change this cable, but could only find instructions on either fresh install or total rebuild, which was waaay overkill for me. So I thought I'd "pay forward" these instructions for the benefit of the next poor bastard in my situation, and so I'd have them for future reference.

Before you start, you should have
  • bike stand (your life will improve!)
  • cable cutters
  • cable tensioner
  • allen wrench(es) for cable attachment
  • light source (e.g., flashlight, or the sun)
  • user manual for your rear derailleur (helpful to see exactly how you should attach the cable to it, and for adjustment tips not covered here)
  • small screwdriver (for derailleur adjustment screws)

I did not lube the cable, since the Jagwires are coated. You may wish to do otherwise depending on your equipment and religion :-) My procedure was:

1. Ensure the chain is on
  • the largest sprocket: the low-normality of the rear derailleur probably did this for you.
  • the smallest chainring.

2. If you can't pull all of the cable out of the shifter, housing(s), and derailleur attachment: cut a long clean piece of the old cable (i.e., with clean cuts on both ends), and reverse-route the old cable to push the old end/barrel out of the "top" of the shifter.

3. Flex the rear shifter's longer lever lever repeatedly until it quits clicking. This "sets up" the shifter for the largest sprocket.

4. Forward-route (i.e., normally route--the reverse of what you did in step 2 if you needed to do that) the new cable through the shifter. I found getting the cut cable end through the "top" or "shifter-end" (away from the housing) of the shifter not too difficult (though you will probably need to shine a light into it), but getting the cut end through the "lower" end of the shifter (toward the housing) I found surprisingly hard. Definitely look at and shine a light through the housing end of the shifter as you route the cable through.

5. Route new cable through all housings to derailleur. This may require the following sequence for each piece of housing (it did for me, anyway) in the cable's run (3 pieces, on the bike in question):

5.1. Route cable through most of housing.

5.2. Remove housing cap at "far end" of housing.

5.3. Route cable through far end of housing, with an inch or so protruding.

5.4. Replace housing cap, and reinsert into frame stop.

6. Retension cable at the rear derailleur (using your cable tensioner), and secure it (probably with an allen wrench). This may be easier if you can refer to your derailleur's user manual.

Status check: at this point,
  • bike is in its lowest gear, chain is on big sprocket and small chainring
  • derailleur cable is connected
  • shifting is not adjusted

This is a good time to check rim true and brake drag, if you're not in too much hurry.

7. Turn the crank arm backward, then check the position of the derailleur's inner/guide pulley. If it's fairly close to the (largest) sprocket, and if your shifting was good before the cable broke, proceed to the next step. Otherwise, turn the derailleur's B-tension adjustment screw (which direction? check its manual) to adjust the derailleur's inner/guide pulley as close to the sprocket as possible without actually touching it.

8. Move the chain to the smallest sprocket (preferably with the shifter!) and repeat the above procedure (substituting "smallest" for "largest" above).

The following step could take more time than all the previous ... or go very quickly. Either way, you might want to take a break before you start on this, in order to be more relaxed.

9. Adjust your indexing. Use the shifter to move the chain to the 2nd sprocket (i.e., the 2nd smallest). Then, simultaneously
  • press the shift lever just enough to engage the cable
  • turn the crank arm clockwise (so as to drive the chain normally)

If the chain is touching the 3rd sprocket and making noise, turn the derailleur's outer casing adjustment barrel clockwise slowly until the noise stops and the chain runs smoothly.

10. Use both shifters to access all sprocket/chainwheel pairs (aka, gears). Adjust the rear derailleur and cable until no noise occurs in any gear excepting the 2 crossover positions: i.e.,
  • largest sprocket and smallest chainwheel
  • smallest sprocket and largest chainwheel

11. Road test!

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