Tiagra Rear Derailleur Repeated Cable Fraying

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AndyK
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Re: Tiagra Rear Derailleur Repeated Cable Fraying

Post by AndyK »

Mick F wrote: 12 May 2022, 3:53pm So ........ mine was an earlier version.
Therefore a backward step by Mr Shimano.
Why a retrograde evolution rather than an improvement?

Seems daft to me.
Who knows. At a guess, I'd say they were trying to reduce the length of cable outer from the frame to the derailleur and also angle the arc of the outer so that it sits nearer to the frame. The Ultegra model I was working on had another gobsmacking piece of bad redesign: a flimsy barrel tension adjuster that's incredibly easy to knacker when turning it under stress (as the previous mechanic had helpfully already done for me). I replaced it with an old-style adjuster from a 105 derailleur. Again Shimano obviously know there's a problem, as the installation instructions specifically say to use a metal (not plastic) ferrule with it. As the metal ferrules are usually slightly thinner and cause less friction, that reduces the chances of accidentally breaking the adjuster by forcing it.
Eyebrox
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Re: Tiagra Rear Derailleur Repeated Cable Fraying

Post by Eyebrox »

It looks as if the RD is bent where the cable exits from the adjuster arm. My 4700 GS mech is shown bottom here.
GridArt_20220512_234232297.png
slowster
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Re: Tiagra Rear Derailleur Repeated Cable Fraying

Post by slowster »

The reason for the more extreme angle of cable exit is, I think, the greater cable pull of Shimano's 11 speed rear derailleurs, which the 4700 10 speed rear derailleur shares.

I suspect that Shimano may have determined by testing that the cables will fray in the STI shifter before they will fray at the rear derailleur (possibly providing the 'cover with tongue' is fitted), assuming normal use, i.e. not riding excessively in smallest or largest sprockets, such as riding cross chained.
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cycleruk
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Re: Tiagra Rear Derailleur Repeated Cable Fraying

Post by cycleruk »

My 11 speed 105 rear mech' cable exit isn't as severe as that.
Not sure, but if the derailleur hanger is bent would that have an effect on the angle of the parallelogram ?
11 speed cassette width fits in a 10 speed space so the mech' movement isn't any wider.
I would check the hanger setting.

I really wouldn't expect the cable to rub on the exit thread but neither can I see the casting being bent to cause this. I think casting would crack if it got bent. :roll:
You'll never know if you don't try it.
AndyK
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Re: Tiagra Rear Derailleur Repeated Cable Fraying

Post by AndyK »

slowster wrote: 13 May 2022, 10:45am I suspect that Shimano may have determined by testing that the cables will fray in the STI shifter before they will fray at the rear derailleur (possibly providing the 'cover with tongue' is fitted), assuming normal use, i.e. not riding excessively in smallest or largest sprockets, such as riding cross chained.
Don't get me started on the fraying cables in the STI lever. "Hey, I know, let's route the cable through a sharp right-angled bend inside the lever where no-one can see it fraying and all the fragments will get stuck in the mechanism, that sounds like a good idea..."
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Mick F
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Re: Tiagra Rear Derailleur Repeated Cable Fraying

Post by Mick F »

Eyebrox wrote: 12 May 2022, 11:46pm It looks as if the RD is bent where the cable exits from the adjuster arm. My 4700 GS mech is shown bottom here.
It looks like we are in accord here.

OP's looks bent.
Mick F. Cornwall
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531colin
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Re: Tiagra Rear Derailleur Repeated Cable Fraying

Post by 531colin »

Eyebrox wrote: 12 May 2022, 11:46pm It looks as if the RD is bent where the cable exits from the adjuster arm. My 4700 GS mech is shown bottom here.

GridArt_20220512_234232297.png
Nailed it!
The hanger for the adjuster is bent......it had already occurred to me that I would be looking at re-drilling it to get a straighter cable run.....probably wouldn't get a useable thread, but a nut will do.

unless its the arm for the pinch bolt which is bent? need to get it next to a straight mech. to be sure!
slowster
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Re: Tiagra Rear Derailleur Repeated Cable Fraying

Post by slowster »

I don't think that the part of the casting for the adjuster is bent. The GS (longer cage) version of the derailleur is designed like that - see the image below of the SS and GS versions side by side.

Image
VinceLedge
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Re: Tiagra Rear Derailleur Repeated Cable Fraying

Post by VinceLedge »

The one on mine is definitely not bent. The cable angle also gets worse when chain is in lower sprockets.
Cable end gizmo ordered! (And another spare cable)
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531colin
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Re: Tiagra Rear Derailleur Repeated Cable Fraying

Post by 531colin »

So, its "long cage" in order to reel in more chain from wide ratio gears.
In order to clear a bigger bottom sprocket, Shimano have angled the parallelogram so the top jockey wheel goes further down as it goes towards first gear; they have then over-compensated and angled the barrel adjuster tab too much, the cable angle in the higher gears is absurd. (in Vince's original picture)
I think i would make sure i set the gears up with that barrel adjuster "all the way out" even fitting an in-line adjuster so I had one to use "on the road" .....and Shimano's "cover with tongue". I would also check out to see if the liner from a Vee brake "flexible noodle" would fit.....i'm staggered that i have never (yet) come across one of those showing any significant wear.

There is still the possibility of re-drilling the adjuster tab, and i would consider doing that depending on the cable angle in high gears.
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Mick F
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Re: Tiagra Rear Derailleur Repeated Cable Fraying

Post by Mick F »

I refer you to my pictures.
Mine was a long cage and not "bent" and out of line no matter which cog or chainring (triple) was selected.
10sp 11-28 and later 12-30 as well as 61/48/34

Granted, mine was an older version.

Just checked in the workshop. I no longer have it.
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531colin
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Re: Tiagra Rear Derailleur Repeated Cable Fraying

Post by 531colin »

Mick F wrote: 14 May 2022, 8:19am I refer you to my pictures.
Mine was a long cage and not "bent" and out of line no matter which cog or chainring (triple) was selected.
10sp 11-28 and later 12-30 as well as 61/48/34

Granted, mine was an older version.

Just checked in the workshop. I no longer have it.
Can the OP buy one like that?
slowster
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Re: Tiagra Rear Derailleur Repeated Cable Fraying

Post by slowster »

531colin wrote: 14 May 2022, 8:30am Can the OP buy one like that?
It would not work with his current shifter. 4600 uses the same cable pull as Shimano's other 10 speed road rear derailleurs and shifters, but (despite also being 10 speed) 4700 uses the same cable pull as Shimano's 11 speed road rear derailleurs and shifters.
iandusud
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Re: Tiagra Rear Derailleur Repeated Cable Fraying

Post by iandusud »

AndyK wrote: 13 May 2022, 12:32pm
slowster wrote: 13 May 2022, 10:45am I suspect that Shimano may have determined by testing that the cables will fray in the STI shifter before they will fray at the rear derailleur (possibly providing the 'cover with tongue' is fitted), assuming normal use, i.e. not riding excessively in smallest or largest sprockets, such as riding cross chained.
Don't get me started on the fraying cables in the STI lever. "Hey, I know, let's route the cable through a sharp right-angled bend inside the lever where no-one can see it fraying and all the fragments will get stuck in the mechanism, that sounds like a good idea..."
I would echo your sentiments. I've just had one fail on me (not for the first time) this week, fortunately at home on the work stand. This is on our tandem and the last failure was about two years ago. I think I'm going to replace them annually as a matter of course. Interestingly I recently replaced a gear cable that frayed at the nipple on one of my bikes that uses bar end shifters. This is a bike that used a few times every week. The cable in question has been on it for 35 years!

Also of note is that our tandem uses a 4700GS rear dérailleur and I've noted the angle at which the cable exits with some concern. However IME the cable fails at the lever first!
Jamesh
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Re: Tiagra Rear Derailleur Repeated Cable Fraying

Post by Jamesh »

VinceLedge wrote: 13 May 2022, 7:23pm The one on mine is definitely not bent. The cable angle also gets worse when chain is in lower sprockets.
Cable end gizmo ordered! (And another spare cable)
You cannot bend a casting it will snap....

Take a file or drill and ease the edge of the casting into a radius. The steel cable should wear the alu casting not the other way around.....
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