Compressionless housing failure
 

The compressionless housing between my FD shifter (Shimano 105) and the downtube mount failed in a way I have not seen before. Some of the wires in the housing punched thru the ferrules (is that the right term?) on the ends of the housings. The ferrules were plastic -- I was used to seeing metal ferrules. This is basically a cross bike, with 2x10 gearing.

So I am thinking I need to replace the cable housing, get some metal ferrules, and call it a day. Am I missing something?


-- Matthew

Long spiral index, or compressionless housing needs a flat bottomed ferrule capable of resisting the action of the wire ends.

There are two common types of failures, which BTW is why I strongly believe it's not suited for brake use.

1- ferrules with the common cause the end on strands to creep toward center. This can bind the inner wire, and eventually cause the strands to extrude through the bottom.
2- even with flat bottomed ferrules, both all metal, and plastic with a metal bottom washer, movement can cause the sharp wire ends to nibble away and erode the bottom until it fails. This kind of failure takes longer, and is less likely if the housing is stabilized at the fitting, so the moving HB/DT junction is more likely to wear through than the RD/chainstay loop.

As to which ferrule is better, that's a toss up. Most metal ferules are all aluminum, and not all have flat bottoms (inside). OTOH plastic ferrules usually (always?) have flat dead stop washers pressed into their bottoms. So it's a toss up, and all I suggest is to replace the ferrules when you replace the housings.

The casing strands punching through the ferrules is pretty common a failure. While usually plastic ferrules we do see steel brake casing ferrules used on gear casings and their weak/thin wall ends also get punched through in due time. (Which is why I only use steel gear ferrules on any 5mm casings, brake or gear).

The fix is straight forward enough. Replace the casing, the ferrules and often the inner cable. Then check their condition more often in the future. Andy.

I have a lot of respect for the other two posters, but I think that the cause of the problem is simpler than that.

Think about a nice flat bottomed plastic end ferrule. Now imagine sticking a slanty cut piece of cable housing into it. All that of compressive force is going to be concentrated on one little edge of the cable housing and it can't handle it.

I don't think that I've ever seen metal ferrules for 4mm shift housing. If they do exist, they're rare. There are millions of bikes using 4mm shift cable housing and plastic ferrules that don't have that problem. That's the common set up. Make sure your housing ends are cut nice and square and my bet is your problem will go away.

Metal 4 mm ferrules exist and I have a bag with a half dozen of them as evidence. Also, the ferrules that Gevenalle (formerly Retroshift) supplies with their shifters are 4 mm metal so somebody does make them. They are all flat-bottomed as expected.

I do agree that the plastic ferrules Shimano, Jagwire and other provide with their shift housing work just fine and i've never had any problems with their failing or with the housing support wires poking through them. Your point about making the housing end cut square and flat is undoubtedly a major factor.

Yes, 4mm metal ferrules do exist. but I never mentioned they did or didn't. I generally prefer 5mm housing for a few reasons, shinny metal ferrules are but one reason:).

When answering many of these types of questions it is easy to assume that most all have the basics already understood, like cutting the casing (brake or gear) square/flat. But I guess some haven't yet learned that one so it's good to remind readers of that need. I use a bench grinder (fine grit wheel) to dress up the ends of my casing cuts. I make sure the plastic liner isn't heat welded shut after with a sharpened (on same grinder wheel) spoke. A well cut and ferrule fitted casing will contribute to a smooth and solid cable action. Andy.

On front derailleurs more than a couple years old you can also misroute the cable at the anchor in such a way that the tension required to move the derailleur is much higher than it should be, and this can lead to early housing failure.

4 and 5mm metal ferrules are available, finishing the casings is critical to ensuring consistent performance and reducing the possibility of the described failure.

On the lower housing run going into the rear derailleur, I bend the housing into the approximate shape it will be when mounted before grinding the ends flat. If you grind it first, the ends will assume a slanted shape when you bend it, since the wires on the ourtide of the bend will have to take a longer path than the ones on the inside. If you cut and grind it when it is bent the ends will stay square.

Thanks everyone -- very helpful! I will replace the housing and stop by my LBS to find set of metal ferrules. I had not thought of grinding the ends flat -- I do have a good cable/housing cutter. The bend is not too severe, but I will also take a look to see if bending it changes the ends much.

I also will look into the cable attachment at the FD to make sure it is done correctly.

Much appreciated!

Good tip. However I've seen more upper casing sections (between shifter and frame) that have the casing strand punch through. I have always thought it's from the twisting that the casing go through during the steering motions. Andy.