Hello!
I have an old Koga Miyata Exerciser from 1991. I've replaced the brake cables and those old rubber seals in the top tube just crumbled...

Does anybody know where I could find those? I emailed Koga - but of course they don't have them anymore...

Cheers
Tom

Koga was not the only ones to use a "rubber" plug cable guide, but the only one with that branding, of course. I can't recall any of the other brands I've seen but I suspect finding ANY replacement will be difficult.
One option might be to get a steel grommet, such as this:
STEEL INTERNAL GUIDE END FOR TOP TUBE :: SMALL PARTS :: BRAZON/SMALL PARTS :: Nova Cycles Supply Inc.
but you may have to modify the opening(s) in the tube, plus to do it CORRECTLY you'd want to braze it in and then you'd have to paint the area(s), but you MIGHT get away with just gluing, the tensioned housing might tend to keep it in place...maybe.

Do you have a photo of this piece outside the top tube? If it's like my Miyata (non Koga) ones then I could send you a file that you can have 3D printed. It won't look exact or have the KOGA logo, but it will work, provided it's the same type.

Hey, now THAT'S an angle^ 3D printing: it just might be the ticket! Not "rubber" but certainly plastic...let us know if you go thru with this project, we'll like to see the results!

Great idea!!! Problem: They are both gone...the rubber was sooo old.

I would bet that they are the same plug, these frames were (mainly) manufactured in the same Miyata factory, so doubt there would be much variation.

I'll snap a picture of my Miyata 512 plug this weekend and get the measurements of the tube too. Hopefully they'll be the same!

Possibly other ideas in this thread: https://www.bikeforums.net/classic-vi...c-inserts.html

If Cinelli ones will work, they're on ebay better price than I found earlier. Search cinelli cable guide

This thread, that's what I'm talking about. If it looks like these puppies, which the previous poster knackered up the SAME way I did mine necessitating the 3D print, you're in luck! If anyone reads this... they twist out, there's no need for pliers

Wow..this could work! They looked a bit different...but maybe worth a try!

here's a picture of how my bike used to look like - the rubber cable guides are pretty long - I don't think the Cinellis would fit

Sort of. Its a multi-step removal process.

Step 1 is pulling up on the cable to lift the end out of the tube. Step 2 is rotating up and to the side. Step 3 is lifting out.

Its hard to do with cable in. I use a smaller phillips head screw driver in place of the cable.

I measured the dimensions. As you can see: not a good option without the rubber guides

maybe those could work, dimensions seem pretty similar Vitus Bikes Zenium Internal Brake Cable Guide 2015 | Chain Reaction Cycles

:

Oh wow, that piece looks like it would do the trick.