1991 Koga Miyata Terrarunner Front derailleur questions

[Roy Kabel]

Hi everyone,

first of all, I'm new to the forum, but have been passively reading it for quite some time now. Thanks a lot for all the great information on here!

Now to my question:
I bought a 1991 Koga Miyata Terrarunner frame, and I'm not sure how fitting the front derailleur works. The cable comes from above over the top tube, but it seems to use a down pull front derailleur. There is a screw behind the bottom bracket between the chainstays, where the inner cable seems to attach. There also seems to be a special screw, that attaches to the derailleur itself, where the outer cable goes in.

There are some photos of this in this thread:
http://www.retrobike.co.uk/forum/viewtopic.php?t=230008

Especially the photos in this post are interesting:
http://www.retrobike.co.uk/forum/viewto ... 7#p1785287

I have just the bare frame, and I have no idea how this works. It would be really nice if someone could shed some light on this for me.

Best,
Roy

 

[FSXStumpy]

The derailleur's cable bolt is replaced with a fitting that acts as a housing stop. The inner cable continues on and bolts to the frame.

When the shifter is actuated, the available length of inner reduces, forcing the outter to pull down the derailleur's arm, thus causing the shift. Essentially the reverse of the standard arrangement where the outer is fixed and the inner does the work.

Likely designed in a time before commonly available top-pull derailleurs.

Finding the housing stop might be a minor trick, but making one would be easy enough if it came to that.

Or you could be sacrilegious and use a top pull derailleur.

J

 

[Roy Kabel]

Thanks for the explanation! Still seems kind of weird to me, never seen this before

I would have no problem with using a top pull derailleur, but I don't know how it would work, because there is no housing stop on the back of the seat tube, it's just a cable guide.

So I guess my best bet would be to make the housing stop out of a bolt with a large head. If you have ideas where to get one or how to best make one, please let me know.

 

[FSXStumpy]

Well, to use a top pull derailleur, you'd need to modify the housing guide just above the derailleur to be a cable stop - A simple insert would do that (shaped rather like a top hat).

If you chose to make an housing stop for the derailleur, and use a bottom pull, I'd take a piece of 1/2" or 3/8" diameter aluminum round bar, maybe 1/2" long. I'd drill it crosswise for the cable stop, and lengthwise I'd drill and tap for the mounting bolt. Depends on what you have access to machine wise. The above could be done easily with a vice and drill press, or with some minor struggle with a hand drill. Obviously, a suitable tap or self-tapping screw would also be needed.

J

 

[Roy Kabel]

Thanks a lot for your input!! I'll see what kind of derailleur I can find and give it a go! Luckily, my brother has good tools and experience working with metal, so I'll ask him for help.

 

[Roy Kabel]

I just found that there are clamp-on cable stops like this: http://www.origin8.bike/product-descrip ... l_uid=5743
Might be a more stable solution than using the cable guide for the top pull derailleur.

 

[legrandefromage]

use a v-brake noodle as a cable guide like my trek:

 

[Roy Kabel]

Hah! That's a nice trick, thanks!
I'll have to think about this a bit. I want to have an as-stable-as-possible solution because this is going to be a world tour bike

 

[chrisv40]

Re:

Funnily enough I bought that frame off LGF and used a problem solver backstop. A bit ugly but 100% secure.

http://www.sjscycles.co.uk/problem-solv ... prod18209/

 

[Roy Kabel]

Yes, I think I'm going to do the same as this seems the most stable to me. I really don't want a self built thing to suddenly fail in one of the more remote areas of the world