Housing cable keeps moving and gets tighter on the derailleur after jumping

Question

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

Answer 1

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.

Answer 2

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?

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.

Answer 3

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.