Bicycle Mechanics - Shifter/cable/loop help!

I could use some help here.

I am adapting my old Peugeut for my wife. It has DT shifters. She likes the top shifters mounted similiar to cyclocross ones that were on her old bike.

So, I moved the shifters over and got some new cable.

Questions: 1) How big of a loop do I make? The cable exits the shifter pointing towards the front of the bike, then must turn and head downward to the deraillers.

2) I have a short length of hard tubing (sheath) for the bend but do I need a piece that extends all the way down? I ask because I can't seem to tighten the cable enough to engage the mechanism.
When it pulls tight, all that happens is the loop shortens so I must be doing something wrong.

Thanks for your help, everyone!

Sheldon

The sheath must be rigidly constrained at both ends: at the shifter and at some
intermediate point or else the cable can't move the derailleur lever enough. In
the absence of down tube shifters you substitute a cable stop at same location
where the sheath ends and is restrained. The sheath loop must be long enough
for a gentle curve from where it exits the bar tape or shifter to the cable stop.
Just guessing this would be somewhere between 15" and 25" depending on
exactly where the new shifter position is. Finding cable stops is a problem.
Modern bikes use "brazeons" or frame mounted stops placed by the frame maker.
Some bike shops may have old stock clamp on types that date to the early '90s
when the change to STI occurred and these were made as a bridge between
downtube and bar mounted STI shifters. www.loosescrews.com has some that
appear to be singletons that may be the same diameter as your frame. They have
to mount solidly as they will slide on the paint or through the paint under the stress
of shifting. You will also need a cable guide at the bottom bracket, which may or
may not be the one provided with the bike. Steve

The sheath must be rigidly constrained at both ends: at the shifter and at some
intermediate point or else the cable can't move the derailleur lever enough. In
the absence of down tube shifters you substitute a cable stop at same location
where the sheath ends and is restrained. The sheath loop must be long enough
for a gentle curve from where it exits the bar tape or shifter to the cable stop.
Just guessing this would be somewhere between 15" and 25" depending on
exactly where the new shifter position is. Finding cable stops is a problem.
Modern bikes use "brazeons" or frame mounted stops placed by the frame maker.
Some bike shops may have old stock clamp on types that date to the early '90s
when the change to STI occurred and these were made as a bridge between
downtube and bar mounted STI shifters. www.loosescrews.com has some that
appear to be singletons that may be the same diameter as your frame. They have
to mount solidly as they will slide on the paint or through the paint under the stress
of shifting. You will also need a cable guide at the bottom bracket, which may or
may not be the one provided with the bike. Steve



Thanks, Steve. I tried using cable ties but they didn't quite do the job. The bike is a 1970's vintage. I'll see what else I can find to hold the sheaths tight.

I appreciate the response.

Sheldon