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Bicycle Mechanics Broken bottom bracket? Tacoed wheel? If you're having problems with your bicycle, or just need help fixing a flat, drop in here for the latest on bicycle mechanics & bicycle maintenance.

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Old 05-22-09, 04:24 PM   #1
spinerguy
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Couple of maintenance questions

These are not trick questions but my current set of (small) problems while working on my road bikes. Any help is appreciated.

First: When replacing a standard double cranks (shimano ultegra) with a compact double (shimano ultegra), do I need to shorten the chain? All other things being equal.

Second: Rear brake cable runs inside top tube, have spent 2 frustrating unsuccessful hrs passing cable through. Any tips??
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Old 05-22-09, 04:51 PM   #2
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yes you' ll need to shorten the chain.try a wire to run though the frame. in the future tape the cable together and pull though.
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Old 05-22-09, 07:24 PM   #3
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Quote:
Originally Posted by spinerguy View Post
First: When replacing a standard double cranks (shimano ultegra) with a compact double (shimano ultegra), do I need to shorten the chain? All other things being equal.
1. You may or may not find it necessary to shorten your chain. Assuming you are keeping the same rear cassette you're only taking 3 chainring teeth out of the equation and only about 1/2 of them are engaged at one time so that cuts the difference to 1 1/2 teeth. You can't shorten your chain by 1 1/2 links. If your chain was on the long side of the tolerance range before, you'll need to shorten your chain by 1" (2 links). If your chain was on the short side of the range previously, you'll want to leave it the same length.

If it was my bike, I'd resize it using the big/big method. Break the chain and wrap it around the big chainring and biggest cog bypassing the derailleur. Figure the shortest place you could rejoin the chain and add 1" (2 links) to that.

If you don't want to break the chain, you might try the little/little chain sizing method. After you install the compact crankset, shift into the little/little combination. If your derailleur is capable of taking up all of the chain slack without the chain rubbing on itself or sagging, you're good-to-go.

2. Lay your bike on it's side with the exit hole for the brake cable on the bottom. Thread a long piece of wire through the entrance hole and watch for it at the exit (a little flashlight helps). When you see the wire, snare it with something and use it to pull the brake cable through the frame.

Next time, leave the brake housing in place and use it to guide the new brake cable through. Then pull the old housing out and use your new brake cable to guide the new housing through the frame.

Last edited by Retro Grouch; 05-22-09 at 07:28 PM.
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Old 05-22-09, 10:50 PM   #4
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Done! (with some help) chain was trimmed a couple of links. It appears to be in good working shape now, big climbing test tomorrow morning is in order.

Thanks much guys.
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Old 05-23-09, 06:51 AM   #5
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My '92 Trek had the rear brake cable threaded through the top tube and I, like most others made the mistake of pulling the housing and cable out together the first time I worked on it. Never did that again.

I found that removing the seatpost allowed me to stick a finger inside the toptube and guide the inner wire out through the exit hole, then used it to quide the new housing in place from the exit end.

Another trick that sometimes works is to apply a vacuum cleaner to the exit hole and feed a thin sewing thread into the entrance hole. The air current will sometimes push the thread out the exit hole. You use that thread to pull a heavier string through and use that to pull the wire.
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