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I've been having some bike issues with a 2016 Trek Allant 7.4 . I'm looking for any documentation about this problem, or any known solutions that don't include externally routing the cable.

 

Long story short is that the gears aren't shifting properly. I've seen it up on the mechanic's stand and within a few minutes he was able to downshift on the shifter and the derailleur didn't budge at all.

When I ride you have to downshift one past the gear you want and then upshift again to reliably get it into gear.

If you downshift a few gears at once, like you might when going up a hill, downshifting one more than you need and then up again doesn't always seem to get you into the gear that's selected on the shifter.

What happens then is that the derailleur changes the gears at some unexpected time to the gear that is actually selected on the shifter. There's a crunch that I'm sure isn't great for the cassette or the chain, and your weight gets thrown off balance.

 

The mechanic I spoke to said that this was a problem with the design of the Allant 7.4. The shifter cable comes out straight at the same angle from the chain stay. It gets bent upward and sits in contact with the quick release nut. The mechanic told me that the problem was due to the sharpness of the angle that the cable was routed after it exited the chain stay.

The same mechanic told me that this problem was addressed in later models. I've attached a photo of the Allant 7.4 and FX-4 routing and you can see that the FX-4 angles the cable upward at the exit from the chain stay. It looks like the FX-4 routing is along a much more gentle curve as well.

 

The shop I bought the bike from has replaced every single component involved in the rear gears (possibly not the external sheath at the back? The manager told me this couldn't be the cause of the problem). The cassette, derailleur, chain, shifters, shifter cable core (now using a thinner core) have all been replaced.

The bike has been looked at by 5 mechanics: 3 mechanics from the store that retailed the bike and stock only Trek bicycles, and 2 mechanics who are Trek employees.

This experience has really put me off internally routed cabling and Trek bikes in general to be completely honest.

Does anyone know of any documentation around this issue? Are there any known fixes?

Allant 7.4 Routing https://archive.trekbikes.com/au/en/2016/Trek/allant_7_4#/au/en/2016/Trek/allant_7_4/details

FX-4 Routing https://www.trekbikes.com/au/en_AU/bikes/hybrid-bikes/fitness-bikes/fx/fx-sport-4/p/21559/?colorCode=grey

My bicycle, rear view of cassette area The cable doesn't flare out to the right that much, I think my phone's camera is giving a bit of a fisheye effect up this close.

My bicycle, side view of cassette area

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    It would be helpful to see a pic of the rear derailer housing loop area on your actual bike. It's very common for too-short or kinked rear loops to cause the problems you describe, especially with this kind of internal routing through the chainstay and out the end.
    – Nathan Knutson
    May 30, 2018 at 4:49
  • Thanks for the reply @NathanKnutson , photos of my bike have been added. I'm hopeful but I'd be a little surprised if this was the cause? 5 mechanics who specialise in Trek products have worked on it without being able to fix the problem
    – Scottmeup
    May 30, 2018 at 5:24
  • Not sure, but if you used a travel agent then it would give a 90 degree turn in 2~3 cm rather than a long loop like that. Downside, they're not cheap. Problem solvers have one for adjusting brake pull, but there's some that just turn the cable.
    – Criggie ♦
    May 30, 2018 at 7:17
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    Everything you describe is classic cable friction. The state of the rear loop does look okay. I know you said you got a new cable, but I think it bears mentioning that it's very common that when there are symptoms of heavy friction and no clear cause, the cable is kinked somewhere inside the housing. I would test it by loosening the cable anchor and feeling with my hands how freely the housings slide over the cable in straight form. Also check to make sure the other piece of housing doesn't have any kinks either.
    – Nathan Knutson
    May 30, 2018 at 16:38
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    One other thing that can cause mysterious problems is if the FD and RD cables get crossed or tangled in the downtube. You can look for this by putting a finger on and tugging an exposed bit of one of them as you shift the other one. You should feel nothing.
    – Nathan Knutson
    May 31, 2018 at 4:49

1 Answer 1

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I agree with Nathan Knutson's comment that this looks like cable friction, but I suspect confirmation bias has everyone looking at the wrong portion of the cable routing.

The mechanic I spoke to said that this was a problem with the design of the Allant 7.4. The shifter cable comes out straight at the same angle from the chain stay. It gets bent upward and sits in contact with the quick release nut. The mechanic told me that the problem was due to the sharpness of the angle that the cable was routed after it exited the chain stay.

The rear derailleur cable routing isn't perfect, but it does not look that bad either. There is nothing inherently wrong with the cable housing touching something. The problem can arise if the housing is severely kinked, which doesn't appear to be the case, I beleive the manager is correct in that this is likely not the culprit.

You also said:

The shop I bought the bike from has replaced every single component involved in the rear gears (possibly not the external sheath at the back? The manager told me this couldn't be the cause of the problem). The cassette, derailleur, chain, shifters, shifter cable core (now using a thinner core) have all been replaced.

This still leaves a couple possibilities:

  1. Cable housing from the shifter to the frame has a kink. You made no mention of whether or not the cable housing (cable outer) was changed. If the housing is a bit short and/or the handle bars get over rotated this can damage the housing. This however should have been obvious from inspection, and I would hope a reputable shop would have looked here first, long before cassettes, derailleurs and shifters!
  2. Inside the frame, you are missing a sheath or the cables inadvertently became entangled during assembly. If the cables are tangled, then this would cause extra friction. You might be able to see this by activating one shifter and looking for movement on the other derailleur. Friction could also be increased if an internal sheath is missing. Most internally routed systems will run the cable inside a sheath to reduce friction. If is missing, then the friction is higher. The shop changed the inner cable, but depending on how this was done, they might have missed these type of problem (e.g., you pull the new inner cable through by using cable that is currently in place).

Typically, internal cable routing results in straighter cable runs and should provide better shifting for longer than external routing.

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  • I agree the cable loop does not bad enough to cause shifting issues described by the OP
    – Argenti Apparatus
    May 31, 2018 at 20:07
  • Thank you very much for the reply. I can say when I saw the bike up on the stand that both the derailleur side and shifter side housing ran free and smooth while the cable core was given slack by being disconnected from the derailleur. I definitely haven't noticed interference from one derailleur shift on the other during rides or on the stand. Examining the inside is probably above my ability. It's been inspected more than 7 times by 5 different mechanics over 3 months, I hope this would have been checked. re: contact with the nut, I think he was highlighting the routing issue that resulted
    – Scottmeup
    May 31, 2018 at 20:22
  • In the brief time that I saw it on the stand the mechanic pulled the cable core through each of the housings and the frame individually, one at a time and it ran smoothly through each. When the cable was reattached to the derailleur it again began to stop downshifting reliably: within minutes I saw the shifter moved down one gear, and the derailleur did not even twitch. From that point the mechanic shifted (the shifter) up-down-up-down multiple times and the derailleur still did not move at all.
    – Scottmeup
    May 31, 2018 at 23:26
  • @Scottmeup If you hang the bike up in a stand, or from cords, can you change gear from small cog to big by pushing the derailleur with your left hand while slowly pedalling with your right hand? Do watch out for moving parts that can bite your fingers. I think you're just going to have to be systematic.
    – Criggie ♦
    Jun 1, 2018 at 3:24
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    @Criggie I was in at the mechanic again today, we were able to change gear from smallest to largest while on the stand by applying pressure to the outer part of the derailleur. We tried a few other things including: replacing the jockey wheel, putting a different model shifter on (shimano slx), putting another cable through (this is the 3rd). There has been no change in the behaviour. We connected the shifter directly to a short length (~10cm) of housing and cable at the back end and weren't able to reproduce the problem in those circumstances. Unfortunately I cannot ride with the sifter there
    – Scottmeup
    Jun 27, 2018 at 9:16

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