At the end of the 80s/beginning of the 90s a few companies made frames with internal cable routing: GT, Scott, Koga-Miyata, etc. but it seemed to go out of fashion. Any idea why? And anyone who continued to use it, other than Klein?
Really? I've not noticed that as a problem with my Karakoram Elite. It does quite a lot of miles in all conditions and the back brake cable is very smooth even with zero maintenance.
I guess its the cost.
There were always some high end bikes with internal cable routing available. But other than the clean look there is no reason for having them.
On the other hand there are so many down sides:
Cost, maintanance time and hydraulic cables might pose a problem so you can not choose to use hydraulic brakes on a frame made for normal cables.
Still, I love my Kleins with internal routing. They look so good
Maybe some is a lot more tricky to deal with than others? I can't remember having any problems at all with my GT, though I have the other one to service soon, so I will pay attention to how easy it is.