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Derailleur cable boot

Old 05-18-18, 01:28 PM
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ted_major
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Derailleur cable boot

I have a 2016 GT Grade alloy, which uses full-length cable housings. The front derailleur cable passes under the bottom bracket and up through the frame between the chainstays, where it has a rubber boot that minimizes water & grit thrown from the rear tire getting into the cable housing:


Front derailleur cable boot
The boot is deteriorating and has started to tear. I contacted GT customer service and they have no information whatsoever about this part. My local bike shops didn't have anything that would fit, either. (A brake cable boot won't work because one end isn't big enough to fit around the flange on the frame, and the cable end is sized for a brake cable, so it won't fit snugly around the cable).

Searches for derailleur cable boot or shift cable boot have turned up nothing. Does anyone know of a source for a replacement? Thanks.
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Old 05-18-18, 02:37 PM
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You need to ask GT who made the frame and maybe get help from them .
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Old 05-18-18, 02:58 PM
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Try your local electrical supply. Measure the Inside diameters of both ends and see if they have a match.

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Old 05-18-18, 03:46 PM
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"I have a 2016 GT Grade alloy, which uses full-length cable housings."
Where does the front derailleur housing terminate? That is something we can't see from the picture. Good stainless steel cable won't rust, but if water penetrates into the housing, the wire in the housing can rust and jam the inner cable. What sort of cable guide is under the bottom bracket? What we can't see from your picture is just as important as what we can see
If I were a GT dealer, I would make sure to stock up on that part. If yours looks like that on a 2 year old bike, there will be lots of problems for owners in the future

Last edited by alcjphil; 05-18-18 at 04:09 PM.
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Old 05-18-18, 07:51 PM
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The housing terminates vertically directly below the flange the boot fits over, pointing straight up. Without that boot, there's basically nothing to stop water and grit from the rear tire from running down into the cable housing. Here's the view from underneath (brake cable on left, front derailleur cable in middle, rear derailleur cable on the right):


Derailleur cable housing
I'll check with an electrical supply house--that might be my best bet. GT's response was "It does not look like we have or stock that rubber boot separately from the bike. Our newer Grades do not come with them."
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Old 05-19-18, 07:01 PM
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While not the same, maybe a Jag Wire Lined End Cap? They have 4, 4.5, and 5mm caps.

https://jagwire.com/products/small-parts/lined-end-caps
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Old 05-20-18, 06:38 AM
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That does look promising. Shimano also has sealed end caps that look like they might work.
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Old 05-20-18, 08:21 AM
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Bikeman Shimano Mega 9 Barrel Adjuster Boot
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Old 05-20-18, 08:56 AM
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Originally Posted by dedhed View Post
The small end of the barrel adjuster boot is sized to cable housing, not cable size.
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Old 05-20-18, 12:08 PM
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V brake boot?
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Old 05-23-18, 01:41 PM
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Thanks for all the helpful suggestions. In the end, I wasn't able to find a direct replacement. V-brake boots don't fit at either end, and my local electrical supply shop didn't have anything (though maybe a better stocked one would?).

Shimano makes a Sealed Cap & Tongue & Rubber Shield that I thought might work:
And it very nearly did work too (if it weren't for those meddling kids . . .), but the boot was too big to fit through the opening in the flange for the original boot, which also doubled as the derailleur cable stop.
What I wound up doing was installing the Shimano sealed cap above the flange and then using a piece of heat-shrink tubing to seal around the joint between the cap and the flange. Time will tell whether it works, but in the meantime, I figure it's better than nothing and probably at least as good as the torn boot it's replacing.
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Old 05-23-18, 08:13 PM
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What is the diameter of the flange that the boot slips on to / over (measured in mm if possible)
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Old 05-24-18, 07:45 AM
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That's a really good question. I wish I'd thought to measure it before I put on the heat shrink. I get ~5mm for the narrow base and ~8mm for the wider top part with the heat shrink in place and the calipers at an angle to fit between the tire/seatpost/chainstays. The inside of the old boot measures ~6mm, insofar as I can measure the diameter of a soft rubber circle.
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Old 12-11-18, 06:02 AM
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Did you ever manage to get hold of the original part ? I have the same issue on my GT Grade. I have had a look around on the web and can't find anyone so far that stocks the part.

Hows the fix with heat shrink and the Shimano part holding up ?

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Old 12-11-18, 01:25 PM
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ever used electrical heat shrink tubing? there ate a few different shrink ratios.
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Old 12-12-18, 10:51 AM
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I haven't looked any further for the original part since the heatshrink/boot fix. A little over 600 miles later, it's holding up fine and looks just like it does in the photos above.
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