I would like to replace a set of Weinmann brake calipers on a Raleigh ladies' bike with newer, modern and more efficient calipers like a dual-pivot one. The problem that I have is that the cable to the rear caliper is routed from the bottom, as seen in the attached images. I have not yet managed to find a suitable dual-pivot caliper so that it would accept the cable coming in from the bottom and not from the top. Do you know of a caliper that would do the job? Any advice, help and/or suggestion would be greatly appreciated.
Honestly, the back brake contributes so little to braking that its not worth fitting a dual pivot.
I'd simply change the brake pads to Kool Stop, maybe run a new inner and outer cable, and leave that single pivot in place. Clean the rim's braking track too.
Dual pivots tend to be more speed orientated, which means racing frames and cables that go in the top. A mixte or ladies frame is not speed focussed. So a bottom-entry dual pivot rear brake caliper would be a rare duck.
You might be able to find some kind of pulley, but for a low-end steel MTB-BSO, new brake pads+cable will be a substantial braking improvement by themselves.
To answer the question - consider using a dual pivot caliper with a travel agent like this, to get the cable around 90 degrees of the bend. I couldn't find one with "more turn"
Web site says "To use our Travel Agent as a friction reducing roller simply route the cable on the outer edge of the wheel and it is smooth sailing for your brakes around tight bends"
Not ideal, but here's a lady's frame used with cantilever brakes and a pulley hanging off the seat clamp, to give some ideas. This would not really fix your problems because the cable still faces upwards.
Finally consider running full housing down, up, and down into your dual pivot caliper. The friction will be higher, but if you use non-compressible housings with teflon then it will help. A couple of cable clamps to hold the outer in place could be useful too.
A third (non-optimal) solution is if you are going to replace the wheel and hub anyway is to get a disc brake compatible rear hub and a rear disc-brake adapter..
With said rear wheel disc brake adapter, a rotor, and a cheap set of mechanical calipers -- you're all set.
This would only make sense if you were replacing the wheel and brakes anyway. Normally discs on the rear are pretty senseless because most of the braking is from the front, but it might be the easiest, cheapest, and most powerful solution here -- if you're already replacing the wheel.
One other (non-optimal) solution is to move the brakes to your chainstays by using the bracket and hole that is there normally for the kickstand.
It's not optimal as that location gets dirty and is hard to adjust the brakes. It's better on mixte designs that have a middle set of stays between the seat and chain stays.
You may need to make a simple bracket out of plate steel or aluminum so that the caliper is at the right place.
Note that you can adjust how close the calipers are to the wheel by varying the distance between the holes in the plate. This means you can use very short reach caliper brakes. Because short reach means higher leverage and because this placement has the shortest and straightest brake cable distance of your other caliper options, you should have the most powerful braking that you can get from a caliper brake -- assuming dry conditions. In wet conditions, the brakes may get so much water kicked up from the front tire to negate this advantage.