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Heat shrink tube; how much heat can brake wire casing take?

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Heat shrink tube; how much heat can brake wire casing take?

Old 09-09-21, 04:48 PM
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tbenjaminsen
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Heat shrink tube; how much heat can brake wire casing take?

Iím looking to clean up the final wiring on my recent road bike build, and Iíd like to use heat shrink tubing to combine the brake wire casing and Di2 cable between the steerer and the entry point at the head tube.

How much heat can really an ordinary Shimano brake wire casing take Ė not to mention the Di2 cable?

Iíve seen it done, Iím just looking for qualified views on if the casing or the cable might take damage from the heat necessary to start the shrinking process.

Iíll be using a heat gun for the purpose.
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Old 09-09-21, 08:25 PM
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I work in the electronics and aerospace industry and have never seen any kind of wire or cable damaged by the heat shrink process. Having said that my preferred method of bundling wires and cables is by using waxed flat lacing tape. The best method of making a "spot tie" is to make a clove hitch over the bundle then lock it by tying a square knot over it.
The running knot type is sexier but takes more practice. https://en.wikipedia.org/wiki/Cable_lacing These methods are far superior to using zip ties; they are lighter, less bulky and less prone to damage the wiring. Unless you make spacecraft harnesses for a living a spool will last a lifetime: https://www.cabletiesandmore.com/nylon-lacing-tape Also works for strapping cables or hoses along the frame and won't scratch your skin or damage the paint like zip ties.
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Old 09-09-21, 08:34 PM
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The cables/housings can easily take the heat required to activate heat-shrink tubing (really doesn't take much). I used it to secure a Di2 wire to the rear brake cable on my G6 - works like a charm and it keeps the cables nice and organized
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Old 09-10-21, 12:35 AM
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Originally Posted by dsbrantjr View Post
I work in the electronics and aerospace industry and have never seen any kind of wire or cable damaged by the heat shrink process.
Originally Posted by BHG6 View Post
The cables/housings can easily take the heat required to activate heat-shrink tubing (really doesn't take much). I used it to secure a Di2 wire to the rear brake cable on my G6 - works like a charm and it keeps the cables nice and organized
Thanks to the both of you!
I'm now assured that the heat won't damage neither Di2 cable nor brake cable, so I'll go ahead with the clean-up job this weekend.

-Tom
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Old 09-10-21, 12:43 AM
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Originally Posted by dsbrantjr View Post
I work in the electronics and aerospace industry and have never seen any kind of wire or cable damaged by the heat shrink process. Having said that my preferred method of bundling wires and cables is by using waxed flat lacing tape. The best method of making a "spot tie" is to make a clove hitch over the bundle then lock it by tying a square knot over it. https://www.youtube.com/watch?v=r_IM844c9SE The running knot type is sexier but takes more practice. https://en.wikipedia.org/wiki/Cable_lacing These methods are far superior to using zip ties; they are lighter, less bulky and less prone to damage the wiring. Unless you make spacecraft harnesses for a living a spool will last a lifetime: https://www.cabletiesandmore.com/nylon-lacing-tape Also works for strapping cables or hoses along the frame and won't scratch your skin or damage the paint like zip ties.
Brings back memories of lacing cables to ladder rack using waxed cord, it was an art. (Former NY Tel technician)
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Old 09-10-21, 04:46 AM
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Originally Posted by tbenjaminsen View Post
Iíll be using a heat gun for the purpose.
I use a cigarette lighter (Bic, I don't smoke, I keep it in my toolbox just for this). Keep it moving, the tubing will shrink pretty quickly. No zipties are necessary. Heat guns, in my experience are simply like using a sledgehammer to drive a wire brad to hang a picture.
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Old 09-10-21, 05:29 AM
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Originally Posted by Badger6 View Post
I use a cigarette lighter (Bic, I don't smoke, I keep it in my toolbox just for this). Keep it moving, the tubing will shrink pretty quickly. No zipties are necessary. Heat guns, in my experience are simply like using a sledgehammer to drive a wire brad to hang a picture.
I use a BIC as well - A heat gun is a bit overkill for heat-shrink
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Old 09-10-21, 06:04 PM
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But you have to thread the cables through the heat shrink tube, then heat it. So the wires and cable housing needs to be detached at one end to slide the heatshrink on.

Instead, I used self fusing silicone tape, (also known as "rescue tape"). I bundled the left and right shifter wires with the wire heading toward the frame downtube. It's a nice, neat loop near the stem junction box, and has lasted for 7 years now! This tape is stretchy and only sticks to itself--there's no adhesive to bleed out later. Cut a small strip, stretch it a bit and wrap it around, and press the layers together with your fingers to fuse it together. I keep the remainder of the roll in a ziploc bag so it stays clean, and it's been useful for other repairs.

I didn't attach the Di2 wire to the brake cable -- I don't think that's a good idea, since they likely move independently when the bars are turned all the way. Try some masking tape to temporarily bundle them together, and see if it's practical, or if the wire gets pulled too far.

Last edited by rm -rf; 09-10-21 at 06:11 PM.
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Old 09-10-21, 06:17 PM
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Originally Posted by dsbrantjr View Post
I work in the electronics and aerospace industry and have never seen any kind of wire or cable damaged by the heat shrink process. Having said that my preferred method of bundling wires and cables is by using waxed flat lacing tape. The best method of making a "spot tie" is to make a clove hitch over the bundle then lock it by tying a square knot over it. https://www.youtube.com/watch?v=r_IM844c9SE The running knot type is sexier but takes more practice. https://en.wikipedia.org/wiki/Cable_lacing These methods are far superior to using zip ties; they are lighter, less bulky and less prone to damage the wiring. Unless you make spacecraft harnesses for a living a spool will last a lifetime: https://www.cabletiesandmore.com/nylon-lacing-tape Also works for strapping cables or hoses along the frame and won't scratch your skin or damage the paint like zip ties.
Originally Posted by JoeTBM View Post
Brings back memories of lacing cables to ladder rack using waxed cord, it was an art. (Former NY Tel technician)
As used on the Mars rover Curiosity! Knots on Mars

It might surprise most people to learn that multitudes of knots tied in cords and thin ribbons have probably traveled on every interplanetary mission ever flown. If human civilization ends tomorrow, interplanetary landers, orbiters, and deep space probes will preserve evidence of both the oldest and newest of human technologies for thousands, if not millions of years.

Last edited by rm -rf; 09-10-21 at 06:21 PM.
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Old 09-10-21, 06:48 PM
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Originally Posted by rm -rf View Post
As used on the Mars rover Curiosity! Knots on Mars

It might surprise most people to learn that multitudes of knots tied in cords and thin ribbons have probably traveled on every interplanetary mission ever flown. If human civilization ends tomorrow, interplanetary landers, orbiters, and deep space probes will preserve evidence of both the oldest and newest of human technologies for thousands, if not millions of years.
I've got a bunch laying on the bottom of the ocean(s).
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Old 09-11-21, 02:54 AM
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Originally Posted by rm -rf View Post
But you have to thread the cables through the heat shrink tube, then heat it. So the wires and cable housing needs to be detached at one end to slide the heatshrink on.

Instead, I used self fusing silicone tape, (also known as "rescue tape"). I bundled the left and right shifter wires with the wire heading toward the frame downtube. It's a nice, neat loop near the stem junction box, and has lasted for 7 years now! This tape is stretchy and only sticks to itself--there's no adhesive to bleed out later. Cut a small strip, stretch it a bit and wrap it around, and press the layers together with your fingers to fuse it together. I keep the remainder of the roll in a ziploc bag so it stays clean, and it's been useful for other repairs.

I didn't attach the Di2 wire to the brake cable -- I don't think that's a good idea, since they likely move independently when the bars are turned all the way. Try some masking tape to temporarily bundle them together, and see if it's practical, or if the wire gets pulled too far.
Sure, Iím aware that the cable/wire combo has to be disconnected at one of each end. Thatís not an issue since this is a bike Iím currently building, and the wire/cable are easily available for disconnecting.

Re. the independence of the Di2 cable, Iíve done a fair amount of measuring and also temporarily attached the cable/wire casing to each other, and thereís no evidence there will be problems with movement to either extreme sides when turning. The trick is to make sure that the length of both the Di2 cable and the wire casing is equal in length and that they follow each otherís natural curvature into the entry points on the frame. On the bike Iím building, theyíre located very close to each other.

The self fusing silicone tape sounds really nice, but I donít trust myself being able to wrap the wire/cable in a nice and even fashion, so I still believe that the heat shrink tube is a good way to go for me. Iím also unsure of the availability of such silicone tape in my region.

Thanks for your input 👍🏻

-Tom
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Old 09-11-21, 07:03 AM
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The tape is available at Lowes and Home Depot.

Here's my setup. Yikes, dust really shows up!
The wires from each shifter cross in the middle, then loop back to the junction box. It's mostly hidden below the bars and stem, out of sight.
I forgot I also wrapped the cable housing and the Di2 wire with silicone tape where they exit the bar tape, just to neaten it up a bit.





Last edited by rm -rf; 09-11-21 at 07:14 AM.
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Old 09-11-21, 08:10 AM
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Originally Posted by BHG6 View Post
I use a BIC as well - A heat gun is a bit overkill for heat-shrink
BIC lighters for heat shrink is for amateurs. You have no control of the heat and can make scorch marks on whatever you're working on. Buy yourself one of these and you'll never look back. It's handy for dozens of other things also. I have one in both workshops - the basement and also out in the garage.

NTE HG-300D Mini Portable Handheld Heat Gun
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Old 09-11-21, 08:21 AM
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Back in my day...

I just use a safety match. Move it slowly closer from underside until it shrinks the wrap. With a lighter or match, use aluminum foil to shield anything near the heatshrink area.
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Old 09-11-21, 08:24 AM
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The only downside to this plan I can see is that brake cables don't last forever and you may have to remove the heat shrink at some time in the future to replace the cable. Perhaps using spaced out short pieces of the heat shrink might make this task easier
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Old 09-11-21, 03:28 PM
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Originally Posted by Jeff Neese View Post
BIC lighters for heat shrink is for amateurs. You have no control of the heat and can make scorch marks on whatever you're working on. Buy yourself one of these and you'll never look back. It's handy for dozens of other things also. I have one in both workshops - the basement and also out in the garage.

NTE HG-300D Mini Portable Handheld Heat Gun
I guess if you have really shaky hands it might be difficult to control a small flame but for the rest of us, shrinking a small piece of tubing without setting your bike on fire doesn't pose much of a challenge
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Old 09-11-21, 10:19 PM
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Originally Posted by dsbrantjr View Post
I work in the electronics and aerospace industry and have never seen any kind of wire or cable damaged by the heat shrink process. Having said that my preferred method of bundling wires and cables is by using waxed flat lacing tape. The best method of making a "spot tie" is to make a clove hitch over the bundle then lock it by tying a square knot over it. https://www.youtube.com/watch?v=r_IM844c9SE The running knot type is sexier but takes more practice. https://en.wikipedia.org/wiki/Cable_lacing These methods are far superior to using zip ties; they are lighter, less bulky and less prone to damage the wiring. Unless you make spacecraft harnesses for a living a spool will last a lifetime: https://www.cabletiesandmore.com/nylon-lacing-tape Also works for strapping cables or hoses along the frame and won't scratch your skin or damage the paint like zip ties.
I restore antique radios and have used waxed dental floss just for wire bundles. But I recall the tape you speak of when I worked on f-111s.
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Old 09-12-21, 05:02 AM
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Originally Posted by BHG6 View Post
I guess if you have really shaky hands it might be difficult to control a small flame but for the rest of us, shrinking a small piece of tubing without setting your bike on fire doesn't pose much of a challenge
You can use a pipe wrench to remove a bottom bracket, too. There are a lot of hacks people use when they don't have the right tool for the job.
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Old 09-12-21, 08:33 AM
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Originally Posted by Jeff Neese View Post
You can use a pipe wrench to remove a bottom bracket, too. There are a lot of hacks people use when they don't have the right tool for the job.
There are many ways to skin a cat, my friend. You can use a heat gun, a BIC, a blow torch, a cigarette, or even a magnifying glass if you were so inclined. The point is, heating a small piece of plastic tubing is an extremely simple task.......for most people
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Old 09-13-21, 06:51 AM
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fwiw my wife's two custom bikes with Di2 came with a ~1.5" section of spiral cable wrap to afix the brake cable to the shifter wire. (E.g., something like this.) Easily removed and/or reinstalled, and allows the two cables to move independently within the wrap if necessary.
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Old 09-14-21, 12:34 PM
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wow you guys are good! fwiw - I've used a skinny soldering iron on heat shrink tubing in some tight spaces. just rubbing the soldering iron along the length of the tubing enough to shrink it tight. (such as repairing broken wires on my cheap computer, on my MTB & securing them so they stay away from the tire & have enough slack, but not too much. it's an ugly mess tho)

old photo but probably similar to current fork & wire repair





also take better care of the fork after swapping it

current iteration





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Old 09-14-21, 12:37 PM
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The metal inside the housing should be able to take far more heat than you can put into it with your soldering iron or heat gun. I can't imagine much harm if the plastic coating gets warm and recools (now under the heat shrink tape).

Mostly the same for electrical wire.
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