Bicycle Mechanics - Derailleur derailed
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07-31-09, 02:50 AM
I installed a Simplex 102 Front derailleur on my Peugeot PRN this afternoon and took her for a ride. What was perfectly adjusted in the house became a sloppy mess on the road, throwing the chain and every thing. When I got home an inspection revealed that the shifter cable is now super-sloppy in the small-gear position and the end is frayed right down to the little bolt that is doing such a sucky job holding the cable in place. I checked this against the MTBs in the house and none of their cables were this sloppy and none of them were frayed. I'm going to "look into this" tomorrow and have two questions:
Is there a better way to secure the cable than simple friction between the bolt and the plate? It doesn't seem to be working that way. I looked to see if there was a hole or something drilled throught the bolt to hold it in place but I saw none. Should I look closer?
How mush "slack" is acceptable in the cable? Should I replace it or just adjust it as it is still "breaking in"?
Is there a way to get/install/re-use the shifter-end stopper so that I can use another length of the same cable? I know that the cables are cheep enough but why waste what you don't have to?
07-31-09, 03:28 AM
I recently had endless fun trying to secure the front derailleur cable on a full-suspension MTB. It simply would not grip. I finally installed a lock-washer under the screw head, which seemed to sort it out. Typically, the cable is secured at the derailleur end by passing along a shallow groove machined in a metal part, and another loose metal part is tightened down on to it with a screw or bolt, or sometimes a nut. You always need to check that you're trying to route the cable correctly to get a straight pull. The MTB I mentioned had it routed incorrectly right from the shop. A nut and bolt (or screw) always need some sort of washer to remain tight, and there are various patterns of lock-washer (internal star, external star, split-ring, etc) which may be added if necessary. I fear your cable may be shot. A good tip is, when you're installing a new cable, to tin the loose end with solder, so the strands won't come apart. This may enable you to remove and re-use the cable after a long period of service, rather than having to replace it. It looks neater, too. A small propane torch may be better for this job than a soldering iron, unless the latter is a large one.
A new cable will tend to stretch at first. It's a good policy to install a barrel adjuster which you can safely reach while you're riding, to make fine adjustments.
07-31-09, 03:37 AM
The 102 is a very nice derailer of good quality... the fixing bolt should not be a problem and in many cases people don't tighten them sufficiently. The cable that passes through should be compressed to half it's diameter if it is to stay put.
If that fails a lock washer could be used but I have never had to resort to this.
If the cable is badly frayed it needs to be replaced and when you set it up the cable should have no slack and the response from the shifter should be immediate.
Cap off the cable with an end or solder it to keep it from fraying... I like solder for the neat and tidy appearance it gives and because it allows you to remove and reinstall the cable easily.
07-31-09, 03:51 AM
48 to 60 inch-pounds of torque to secure the cable with the pinch-bolt for an FD. I go for 60 myself. I do suggest that, as the cables will (many, many times regardless of torque) settle/stretch and the housing too, that you install a barrel-adjuster (BA) along the cable-line between the shifter and the FD. Every time you have to release the pinch-bolt and pull the cable - the more it gets worse in my findings. So torque it down and use the BA should/when it goes weak again.
Here a photo of a BA I installed due to this very problem:
And here is where I bought a bunch to keep in stock:
07-31-09, 09:03 AM
Not meaning to hijack the thread but a follow up question on cable soldering.
I have tried it, using a MAPP torch and APPARENTLY I can't get the cable hot enough to melt the solder. Is there a certain type of solder that should be used for this application?
07-31-09, 09:13 AM
I use Multicore solder, as used for electrical and electronic work (I'm a radio ham). I also use a 25-watt iron quite successfully. With a torch, you have to be careful of the outer cable sheath, the bike's paintwork, etc. Multicore has cores of flux incorporated in the solder, but you could use separate flux. Essential to clean the wire thoroughly, then degrease it - I use fuel for a cigarette lighter, which comes in a handy dispenser with a narrow nozzle. I'm not sure that all types of cable available will take tinning, although all the ones I've tried have. By the way, avoid lead-free solder (did you ever hear anything as daft?). Proper solder is made from lead and tin, and is what you need.
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