trunolimit

Hello,

I'm asking probably the silliest of questions but what's the danger with using a shifting cable as a break cable?

I'm using a Shimano ST-5700 shifter. I installed a shifting cable for lack of a break cable and everything seems fine. Am I causing unseen damage somewhere?

FBinNY 

Causing damage, no, but increasing your risk of failure.

To begin with a shifter wire is typically 1.1mm in diameter vs. a brake cable's 1.6mm. That's roughly 1/2 the strength using the same material. Would you want to hang from a rope rated at 1/2 the load that was recommended? So you're running with 1/2 the strength, which will lead to premature weakening and failure, which always and happen at maximum load, or during an emergency stop.

There's also the question of the fit of the head into the lever's fitting. Gear and brake cables use different fittings and your gear fitting is smaller, creating a risk of it pulling through, or if the lever has a side exit, popping out that way.

So, while it's better than nothing and OK in a pinch, you want to go back and install a proper brake cable at the earliest opportunity.

Just Riding

Shift cables are typically about 1.1mm in diameter, and brake cables are about 1.5mm in diameter. A brake cable has nearly twice the cross sectional area as a shift cable. Using a shift cable as a brake cable may give you an unlucky break.

dsbrantjr

By shift cable do you mean the inner wire or the outer housing or both? If you have used shift housing for a brake application you risk sudden failure of the housing under hard braking, which is exactly the worst time. From Sheldon Brown:

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. Full article: Cables

fietsbob

With the access to write about it, getting the right replacement is not difficult . you should ride carefully to the Shop & Buy the Right cable.

trunolimit

Ha I se what you did there. lol

Alright I'll go and buy the correct cable and housing. Didn't even know the housing was in question. Jeez thanks for the info.

trunolimit

Another question. When cutting the housing I've always just used metal cutting snips. I see this break cable set and it says "SLR cuttable housing" is there housing out there that is not cuttable?

spdracr39

Cables

DOS

How did you attach cable to the brake levers given that brake cable ends (ABC in pic) are considerably different than shifter cable end (DE)?

trunolimit

You see how C is sort of drum shaped? On my st-5700 there is a piece that looks like that with a hole in the middle. the shifting cable fit right in that hole.

Yan 

Take a taxi to the bike shop. Your bike is currently brake-less.

FBinNY 

This is probably unnecessary. The gear cable is roughly half as strong as a brake cable. Critical parts are built with very generous safety margins and brake cables are probably designed so as not to be tensioned anywhere to half their breaking strength.

So the OP is reasonably OK for the short term, but he's flying without a net.

trunolimit

I love this guys site. I feel like a cable routing master now.

Yan 

Would you be willing to be liable, should he be killed? If not, you shouldn't give that advice.

Would you be willing to climb the below with a half strength rope? The consequences are equal to using a half strength brake cable. It'll snap when you apply emergency pressure, precisely when you need the brake the most. If you are lucky, you will simply crash. If you are unlucky, you will end up under a semi.

FBinNY 

Adults getting advice on the net have to make their own decisions. I explained about the risks in my initial post.

But risk isn't digital, it comprises a spectrum, and continually exaggerating lower level risks makes it harder for people to discern the real serious high likelihood risks from lower ones.

In any case there's redundancy in brakes, and the realistic liklihood of simultaneous dual failure is pretty low. In the context of all the things that can happen riding a bike, a short ride with this cable doesn't represent a major spike in total risk.




....

trunolimit

Point taken. My rear breaks are still good so that'll get me home tonight. I only used the shifting cable on the front because I had to replace the bolt that clamps down on the cable and I didn't have any other cable left.


So looks like I have a big project ahead of me. Replacing my whole rear drive train and now I am going to re-cable my bike because according to Sheldon Brown I did it all wrong. And it would explain a lot of the mysterious issues I have been having with my shifter. Like for example sometimes I'm trying to shift up or down on my rear and there is no tension on the shifter. I attributed it to being old and going bad so I'm upgrading. But if it's a problem with my housing and routing of the housing then that'll be interesting.

JanMM

BRAKE and BREAK sound the same but are different words with different meanings.

Yan 

I respectfully disagree. Risk isn't digital, but life is. You can argue that I'm exaggerating and that a crash might only result in slight injury; but the nature of the accident is determined by coincidence and out of our control, therefore we assess the risk as the highest possible: death.

When I'm risking death, I don't go out of my way to reduce my margin of safety. All other points about probability are moot.

It is true that I am accepting a certain level of risk by bicycling on the road at all. Indeed, there is risk in any activity. I don't have a problem with risk, but I want to die when I've made sound choices in the face of calculated risk. I don't want to die because I used a shift cable as a brake cable.

Andrew R Stewart 

So there is a once common use of a shift cable for a brake cable which us old timers already know about. But there's a reason why it is ok and didn't have any more real life issues compared to brake sized cables.

Mafac branded center pull brakes used a straddle cable sized the same as a shift cable for years. Many thousands of bikes were equipped with these brakes. many mechanics BITD replaced this straddle cable (often to lengthen it for what ever reasons) with a then standard shift cable. This was fine and still is. Why? Because the load/tension is split between the two 'sides' of the straddle cable. The primary brake cable was a standard sized brake cable.

So the take away is that if you're going to use a shift cable for a brake, use two.

PS- the other application for a shifter cable as a brake cable is more current (and I just thought of it). Tandems often have a drag brake which is controlled by a friction shift lever (bar end is my preference), Many have used a shift cable (whose end fits the bar end lever properly) for this. BUT (and it's a big but) this application doesn't have the tension and cycling of on/off tensions to the degree of a brake designated to stop the bike.

So take away #2 is that if you don't want to actually stop the bike and plan to use a shift lever to set and then consistently use the brake (which is how a drag brake is used) then you're fine with a thinner and weaker shift cable. Andy.

zebede

YES, I had forgotten.....I set up my old Burley tandem with a thumb shifter and a derailleur cable for the drag brake. On one hand the mass to stop is MUCH greater than a regular bike AND would be primarily applied in high speed down hill runs! On the other hand it had th3 proper cable end, triple redundancy (two rim breaks) and was well maintained.

Looigi

A shifter cable will work well as a break cable, but not as a brake cable.

HillRider

I wouldn't be as concerned about the shift cable's smaller diameter and lower tensile strength as I would be concerned about the small end fitting pulling through the brake lever's anchor drum under a hard pull. And, yes, brake and break aren't the same word.

trunolimit

You mean a break cable would work as a shift cable but a shift cable won't work as a break cable?

Andrew R Stewart 

Yes but... if the shifter was indexed the brake cable which is about 50% larger in diameter, won't allow for consistent indexing. And the larger head might hang up within the shifter too. Andy.

HillRider

No, the comment was pointing out that a shift cable can break (i.e. fail) if used as a brake (a device to slow or stop you) cable. You don't seem to get the spelling differences between the two words.