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I've recently serviced my bike and the derailleur cable/housing keeps getting tighter and tighter until the ferrel on the cable starts bending. I've noticed it happens after I bottom out my rear suspension. At home I pull the cable through the frame so that there is a lot of extra housing near the derailleur area to give it some more slack. However, during the ride it remains fine but eventually the cable/housing gets tighter and tighter and my shifting performance decreases. Does anyone know why this is happening? The cables and housing were replaced yesterday so they are brand new.

As you can see in the photos, the housing and gear cable is pretty long so there's no problems in length (I think) 1st image: what it looks like after riding 2nd image: after fixing it 3rd image: lots of room for cable at the front near shifter enter image description here enter image description here enter image description here

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    Clarify please - your bike has one piece of outer housing that runs the full length through the frame?
    – Criggie
    Oct 30, 2021 at 12:38
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    If it’s continuous housing: Can’t you tie it in place with cable ties? If it’s not continuous housing: How is the housing able to slip? Do you have good housing end caps in place?
    – Michael
    Oct 30, 2021 at 17:13
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    Is there no barrel adjuster on the RD. It looks as if the end cap sits in the threads where the adjuster ought to be.
    – Carel
    Oct 30, 2021 at 18:15
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    @Carel excellent spotting - that needs to be fixed or indexing gears becomes extra-hard.
    – Criggie
    Oct 30, 2021 at 22:16
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    It's a mtb Deore real derailleur... most of them don't come with rear barrel adjusters, only front adjusters at the shifter
    – Nicksamios
    Oct 30, 2021 at 22:58

3 Answers 3

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It's happening because some area where the housing contacts a frame member or housing port is pulling on the housing when the suspension actuates, but not releasing it on the return.

There is no singular trick to fix this. Assuming the housing setup is as-intended, it's a design problem.

Here are some things you can try:

  • Figure out where the catch is happening if possible. You may be able to do this by manually cycling the rear end in the workstand. When I've seen it, it's typically been in the BB area.
  • Somewhere between that spot and the RD, you can look for any zip tie guides that could be made to grip the housing tighter, such that they disallow it from slipping it up like it is now. You could sneak in a piece of rubber shim, skateboard tape, etc where the contact with the frame is. Or you might just find that the zip tie is too loose.
  • You could invent a new spot to anchor the housing to the frame based on the same principle, but be careful you don't create a situation where the suspension travel is causing the cable to also kink as a result.
  • You could look for ways to make the catch spot have less grip on the housing. One idea is put on a piece of heli tape or similar where the contact is occurring.
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You need to feed extra housing to the back of the bike. Having so much of it where it meets the shifter isn't going to help and is likely a source of the friction you describe.

How does your internal routing setup work? Some more photos of the entire cable run would be nice. Hopefully, there is a clamp or something that can keep the required amount of housing available back there. If not, we're going to have to invent something.

For example, on my bike, the rear brake hose needs extra length. I determined this length by depressurizing the shock and cycling the suspension through its travel. The clamped port at the top left corner prevents the extra from escaping back into the frame, while the zip tie setup near the BB prevents it from rubbing on the frame. Perhaps your frame has a similar arrangement possible?

enter image description here

Lots of suspension designs need extra housing length as the linkage compresses. The issue here isn't the fact that the housing is being pulled per se, but rather how your bike is fulfilling that need.

Also, you might want to inspect the housing where it enters the derailleur. That bend in photo #1 is not healthy. Sorry to see that happening to new cables.

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  • Thanks for your answer. I took all the air out of the shock and set the housing to the appropriate length. I also put electrical tape on the housing where it exits the frame and now the housing doesn't 'pull' at the derailleur even when I bottom it out.
    – Nicksamios
    Oct 31, 2021 at 8:03
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    @Nicksamios Nicely done!
    – MaplePanda
    Nov 1, 2021 at 3:00
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I wonder if there's a clamp somewhere that was missed when the new outer was installed. Check around the BB for a cover, and see if there's anywhere that looks like a ziptie mount or similar.

Another possibility is that the new outer has a slightly smaller outer diameter than the original cable, and has just enough tolerance to slide.

A good blob of hot-melt glue around the outside of the outer, at the point the cable enters the frame should add enough resistance, and is relatively easy to remove. If that helps but isn't durable enough, a blob of epoxy in the same place may be more durable.

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    I've checked and they've gotten every mount point with the zip ties, they are pretty tight as well. I think you may be correct about the diameter of the housing. I suspect the manufactures made the exit point for the housing a little too big.
    – Nicksamios
    Oct 30, 2021 at 22:56
  • @Nicksamios you could try scuffing the outer surface of the housing with some sandpaper to make it less slippery. That alone might help, or will add "tooth" for the hotglue to stick to.
    – Criggie
    Oct 30, 2021 at 23:05
  • is it bad for the housing to not move? Does it need to have some kind of movement especially with a dual suspension?
    – Nicksamios
    Oct 30, 2021 at 23:06
  • @Nicksamios Well it is moving now, but only in one direction as the suspension flexes. You either need it to move in both directions, or restrain it from moving too far in the forward direction.
    – Criggie
    Oct 30, 2021 at 23:29

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