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Rear Derailleur cable housing

Old 05-09-21, 07:36 PM
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williamskg6
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Rear Derailleur cable housing

I've been working on a 1987 Specialized Sirrus. I've got it assembled and working, but I'm not very satisfied with how the rear derailleur cable housing is working out. On the bottom of the right chainstay there is a brazed on cable stop, but the it does not work with a end cap for the housing. If I use a housing end cap it works fine but it cannot fit within the fitting and it just sits awkwardly on the edge of the fitting. It's not even close. If I go without a ferrule the cable housing will eventually wiggle into the fitting. Problem solved, right? No. Without a ferrule, the housing will eventually go all the way through the fitting and shifting doesn't work correctly anymore.

Here are some photos so you can see what's going on.




Either I'm doing something wrong or this is how it's supposed to be done. If anyone has advice on the correct way to do this, I'd love to hear about it. Thanks!
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Old 05-09-21, 07:42 PM
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You need a step down ferrule. LBS should give you one for free.
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Old 05-09-21, 07:42 PM
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You need a 'step-ferrule'.
Step ferrule
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Old 05-11-21, 02:00 AM
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You need a terminal step down cap or step-down ferrule.
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Old 05-13-21, 08:45 PM
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I did some measuring and the inside diameter of the fitting is 4mm. The outside diameter of the derailleur cable housing, as I'm sure you all know, is 4mm. I could not find any of those Shimano 4mm step ferrules locally. The closest thing I could get is a Jagwire ferrule that has a very thin tube on the end. It accepts 4mm housing, and the thin tube is just a little bigger than the cable. What I did is get a piece of vinyl end cap for some carbon rods I used to use on kites and put it on the thin tube. That brought the outer diameter of the tube to about 3.8mm, which is reasonably close to the size of the frame fitting. It's not perfect, but it's a ton better than what I had. Here's a photo. You cannot see the vinyl end cap piece - I cut it such that it's entirely within the frame fitting. This will definitely work until I decide I want to track down some of those step down ferrules.

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Old 05-13-21, 08:50 PM
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There's an Amazon link in my post.
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Old 05-13-21, 09:18 PM
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Originally Posted by cxwrench View Post
There's an Amazon link in my post.
I did see that, thanks. I was just trying to find something local. I'm glad you put the link in there though - these are not very easy to find.
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Old 05-13-21, 11:32 PM
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Originally Posted by williamskg6 View Post
I did some measuring and the inside diameter of the fitting is 4mm. The outside diameter of the derailleur cable housing, as I'm sure you all know, is 4mm. I could not find any of those Shimano 4mm step ferrules locally. The closest thing I could get is a Jagwire ferrule that has a very thin tube on the end. It accepts 4mm housing, and the thin tube is just a little bigger than the cable. What I did is get a piece of vinyl end cap for some carbon rods I used to use on kites and put it on the thin tube. That brought the outer diameter of the tube to about 3.8mm, which is reasonably close to the size of the frame fitting. It's not perfect, but it's a ton better than what I had. Here's a photo. You cannot see the vinyl end cap piece - I cut it such that it's entirely within the frame fitting. This will definitely work until I decide I want to track down some of those step down ferrules.
Itís questionable if that will work for index shifting. You need a stiffer ferrule. The plastic one is going to flex and make for vague shifting.
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Old 05-14-21, 06:22 AM
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I think this is the one area that does not have much attention given. It is always a challenge to ensure there isn't an abrupt change in direction of the cable.
I went round and round when building the De Rosa. The cable set is Campagnolo and didn't have very clear directions for the use of the parts.
In addition, I was surprised to see the difference of the angle depending on which sprocket the chain was on. Here is an example. You might suppose the best angle would be with the largest sprocket as the RD ends up being stretched out.
P1050081 on Flickr
P1050082 on Flickr

The last picture is with the worst configuration as the chain is still on the small ring. Now on the large ring:
P1050083 on Flickr

Some might say the housing is too long. The wear on the stay indicates a shorter housing. I try to make sure the transition are as straight as possible. Perhaps I should look at a compromise. The truth is that the housing is uncut from Campy.
In any case. when you select the length of the housing, take into account which sprockets and chain ring you are set up with for the worst angle.

Yeah, I know, trim the cable!
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Old 05-14-21, 06:40 AM
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Originally Posted by cyccommute View Post
Itís questionable if that will work for index shifting. You need a stiffer ferrule. The plastic one is going to flex and make for vague shifting.
Well, the new ferrule and the small tube are both metal. The vinyl end cap part I mention is only to keep the metal parts somewhat centered in the frame's fitting. It's not perfect, but an improvement.
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Old 05-14-21, 07:21 AM
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Originally Posted by SJX426 View Post
I think this is the one area that does not have much attention given. It is always a challenge to ensure there isn't an abrupt change in direction of the cable....I try to make sure the transition are as straight as possible. Perhaps I should look at a compromise.
You might like this article from Killasgarage.com. I was led to it by Bike Gremlin. It concerns the bends in a cable housing and total degrees of direction change. A teaser picture from the article:

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Old 05-14-21, 09:17 AM
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Originally Posted by williamskg6 View Post
Well, the new ferrule and the small tube are both metal. The vinyl end cap part I mention is only to keep the metal parts somewhat centered in the frame's fitting. It's not perfect, but an improvement.
Given the angle of the ferrule, you are putting strain on the plastic part of the ferrule. The plastic part is the only thing that is really engaging in the stop. The plastic is going to cause a kink on the inner cable as pressure is put on the cable.

A step ferrule will keep the cable housing in a straight line. Your current workaround will bend and put pressure on the cable which will have an effect on the precision needed for index shifting.
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Old 05-14-21, 09:54 AM
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Originally Posted by cyccommute View Post
Given the angle of the ferrule, you are putting strain on the plastic part of the ferrule. The plastic part is the only thing that is really engaging in the stop. The plastic is going to cause a kink on the inner cable as pressure is put on the cable.

A step ferrule will keep the cable housing in a straight line. Your current workaround will bend and put pressure on the cable which will have an effect on the precision needed for index shifting.
I do get what you're saying, but there are no plastic parts in the ferrule. It's all metal. The only plastic is the vinyl end cap that I used on the exterior of the thin metal tube to keep it centered in the frame fitting, and that does not come in contact at all with the cable. I do agree that it's not ideal, so I will be putting a step down ferrule on there as soon as it arrives, but it's better than it was.
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Old 05-14-21, 10:02 AM
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I’m glad you are getting the correct part. If you have an old set of brake calipers you don’t care about, you might be able to fashion something that will work from the cable adjuster.

Or you can just wait for the step ferrule and sell the old brakes on eBay for 10 times their worth.

John
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Old 05-14-21, 02:12 PM
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You could get a rollamajig that will pass the cable through a pulley at 90 degrees and directly into the derailleur. Then the cable housing will be almost but not completely straight. Although it's plastic, mine is still ok after 3 years. I bought 2 extra just in case. I also use it for the front derailleur because I have no cable stops on the frame.

If you want metal, there are some cheaper aluminum pulleys that you can find on aliexpress with radial bearings.i bought a couple but never got around to changing them because the original rollamajig still works and are smaller and lighter.
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Old 05-18-21, 03:59 PM
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Well, the step down ferrule arrived today, and I noticed I had a problem - the stepped-down section was 5.6mm and would not fit. My frame fitting has a hole that is 4mm. Looking at the part, the stepped down section was thick enough metal that I could file it down. So, I made a mandrel for my Dremel and filed down a portion of the stepped-down section. It looks a little rough in the photo below, but on the bike it looks just fine since the rough finish part is inside the frame fitting. I need to get a lathe at some point!




I shortened my cable housing a bit, made some B limit adjustments, and shifting is working very well. A modern 1X drivetrain on a 30 year old bicycle!




Thanks to all who offered advice, and a special thanks to Joe The Bike Man.
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Old 05-18-21, 10:56 PM
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You guys are all using 5 to 4 mm step-down ferrules. 5mm shift housing would fit snugly into the 5mm end of the ferrule, resulting in less dirt and movement of the housing end inside the ferrule. Since fewer applications call for step-down ferrules these days, there isn't much call for 5mm shift housing. But it is available.
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Old 05-19-21, 03:47 AM
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Originally Posted by williamskg6 View Post
Well, the step down ferrule arrived today, and I noticed I had a problem - the stepped-down section was 5.6mm and would not fit. My frame fitting has a hole that is 4mm. Looking at the part, the stepped down section was thick enough metal that I could file it down. So, I made a mandrel for my Dremel and filed down a portion of the stepped-down section. It looks a little rough in the photo below, but on the bike it looks just fine since the rough finish part is inside the frame fitting. I need to get a lathe at some point!




I shortened my cable housing a bit, made some B limit adjustments, and shifting is working very well. A modern 1X drivetrain on a 30 year old bicycle!




Thanks to all who offered advice, and a special thanks to Joe The Bike Man.
I think you did a great job at modifying the part.
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