# Using brake cable housing for derailleur cable?



## DRLski (Apr 26, 2003)

Is there any real reason to not use brake cable housing for derailleur cable? Will it work?


----------



## juicemansam (Nov 26, 2007)

When I built my bike earlier this year, I didn't measure the cables and cut away. I found that I didn't have enough housing for the RD end. I ended up using the thicker brake cable housing for that 6-8" length. The only problem I have with it is that I know it's brake cable housing, other than that I have had no problems with it.


----------



## DRLski (Apr 26, 2003)

I'm in the same predicament, not enough derailleur cable housing, plenty of brake housing. Unless anyone else knows of any problems with using it I may give it a shot. Thanks.


----------



## serfur1 (Sep 17, 2007)

from Sheldon Brown:

Compressionless "Index-compatible" Housing
With the advent of indexed shifting combined with handlebar mounted shift levers, it developed that conventional housing was a source of imprecise shifting. This is because the effective length of the housing changes as it is bent. This is not a problem with brakes: Although sometimes it will be noted that rear brakes may drag slightly when the handlebars are turned all the way to one side, you can't turn the bars that far when the bike is actually in motion.
This small variation in housing length was too much for reliable indexed shifting, however, so Shimano introduced "S.I.S." housing, now widely copied by other manufacturers. This type of housing does not consist of a single spiral-wound wire, but a bundle of wires running pretty much straight along parallel to the housing. They are held in place by the fact that they are sandwiched between the plastic housing liner and the plastic outer covering.

"Compressionless" housing doesn't change length significantly as it is flexed, so the indexed shifter is able to communicate the correct setting to the derailer, even as the handlebars are turned, and the loops of cable housing bounce up and down due to bumps.

Warning: Since compressionless housing relies on plastic to hold it together, it is not as strong as conventional spiral housing, and should never be used for brakes! The loads applied to brake cables can easily cause compressionless housing to rupture and burst, causing a complete and sudden loss of brake function.


----------



## krisdrum (Oct 29, 2007)

Should be fine, as brake cable is stronger. However you can't go the other way, shift housing instead of brake housing.


----------



## MR_GRUMPY (Aug 21, 2002)

It will work fine for friction shifting, but is not recommended for indexed shifting.


----------



## raymonda (Jan 31, 2007)

krisdrum said:


> Should be fine, as brake cable is stronger. However you can't go the other way, shift housing instead of brake housing.


Wrong, wrong, wrong! You can not use brake housing for index shifting and expect your shifting to work properly due to the correct reasons mentioned in an earlier post.


----------



## Mr. Versatile (Nov 24, 2005)

I use it interchangeably on my commuter. But as Grumpy pointed out, my commuter has friction shifting. On my indexed bikes it's a no no.


----------



## DRLski (Apr 26, 2003)

hmm, I installed it this morning with brake cable and it seems to be shifting okay to me, I'll have to take it out on a ride and see if it acts up.


----------



## raymonda (Jan 31, 2007)

And I don't need any on my single speed. When I walk I don't even need brake cables.


----------



## Treker (Nov 7, 2007)

In the good old days of friction shifters, there was not even a difference in the cable housings used for brakes and shifters. It was all one type. As mentioned in the Sheldon Brown quote above it became necessary to have a more precise type of cable housing for use with index shifting once they came along.

That being said, if you are only using a short length of brake cable housing in your run of mostly shifter cable housing with an indexed system, you should be fine. If you run into problems you could always replace it with the proper housing later on. However, it will not be operating "as designed". Make this substitution at your own risk.

Jay B.


----------



## sml (May 21, 2007)

DRLski said:


> Is there any real reason to not use brake cable housing for derailleur cable? Will it work?


No.

The cable diameters for brake and derailleurs are different. The brake cable housing will be too large for a derailleur cable.


----------



## brblue (Jan 28, 2003)

*It works*

.. ok. Tiagra drivetrain. Brake housing for brakes and deraillers. LBS' around here (which I am not fond of) sell the same type of housing (brake housing) both for brakes and shifters. The drivetrain has all in all an agricultural feel but the shifting definately works with this type of housing. It doesn't shift by itself or fail to get in any particular gear.
Though it's better to use the shifter cable housing if you got one...


----------



## dead flag blues (Aug 26, 2004)

Go to your LBS and pony up for a few feet of bulk D cable.


----------



## PeanutButterBreath (Dec 4, 2005)

sml said:


> The brake cable housing will be too large for a derailleur cable.


Think about that for a second -- the housing can't be "too large" for the cable. Theoretically, it can be too large to interface properly with shifters and dérailleurs, but this is ususally not the case and in fact you can buy 5mm OD dérailleur housing.

That said, there are a lot of things you _can_ do that you shouldn't unless you have no choice.

If you grab the brakes on a bike and squeeze the lever as far as you can, you can see the exposed lengths of housing flex. Whether you notice the impact that this will have on your shifting or not, its not helping.


----------

