Mechanical Disc Replacement Brake Cable Help

Yay. I do like a happy ending.

OP: some good advice above, some downright wrong. From extensive personal experience, the Yokozuna Reaction cables last years, remain friction-free, and offer damn-close-to hydraulic levels of performance. I recently descended a 1-in-4 Scottish road with multiple switchbacks, at speed, and had one finger on each lever, with no issues slowing down. 

http://road.cc/content/review/205547-yokozuna-reaction-brake-cable-system

I have had rub issues before when the pistons themselves get a bit sticky, TRP advised me to clean/lube the sides of the pistons with a mineral oil-soaked cotton bud whilst going through cycles of retracting and over-extending the pistons.

You can successfully run standard Shimano cables with these brakes, may not be as good as compressionless, but you can get them working well.

The pads are the same ones as fit Shimano Deore , can get them cheap from superstar components or uber

Also I strongly recommend doing the overfilling thing if you have too much throw. Took me 18 months of fettling and then riding on lacklustre brakes, now I've done this they are excellent. 

Scoob_84, neither of the cable kits you link to are compressionless. However, these two are:

https://www.ribblecycles.co.uk/trp-disc-brake-cableset-compression-less/

http://www.highonbikes.com/jagwire-road-pro-brake-cable-set.html?gclid=E...

My recommendation would be to go with the TRP kit, I have installled one recently and it's very good.

For cutting the outer, yes you need a decent cable cutter. If you can put an old piece of brake inner through the outer at the point where you're cutting, you'll avoid crushing the outer flat.

Mikethebike, you might think that 'posh' cable is only a little better but I can assure you that when it comes to cable discs, the difference in performance between conventional outer and compressionless outer is night and day.

Regardless of the cables you buy you'll need a good set of bike-specific cable snips, a file, and a braddle (sp?).

Even with bike cable snips you'll find that you'll get a rough end to the cable where you cut it and you need to file that off. The outer will also deform a fair bit so you need to stick something in the end after cutting it to get it back circular. 

As others have said, use your old outer to measure the new one. To minimise the cable crushing I always stick the old inner cable in the new outer before cutting the outer - probably doesn't make much difference if your snips are good but definitely reduces the crushing. It also means you don't end up making the newbie mistake I did and cut the new outer with the new inner installed!

Also a good time to check the calipers are aligned - just loosen off the two mounting bolts, pull the brake on hard, and retighten.

I remember being really intimidated by brake alignment and cabling and loathe to mess around with any adjustments but its pretty simple once you've done it once or twice

Your brakes are hydraulic by the way, so the problems may not be cable related, although they do have a cable element. The pistons may not be retracting, or the whole unit may be misaligned. Also check the pads are correctly in place, they should be held in by a locking pin or screw.

If you do replace the cable and outers, use the old one as a template for how long, how much outer to use, and where to put the cable stops etc. You will need a decent set of cutters. Any reasonable cable and outer will work, i.e jagwire or shimano.

Gear cable housings are usually compressionless (lengthways reinforcing).  Brake housings are often spiral bound and do compress.

I have Yokozuna Reaction compressionless housings on my TRP Hy/Rd brakes. Performance is greatly improved, although at a price.

Contraband is correct, standard brake cable is poor for mech discs, you need compressionless. Jag wire do one, there's TRP disc connect, one or two others. Don't ignore this advice! You'll need to web search for the correct disc pad, there are loads of variants.

Wrong, there's a huge difference in performance between standard brake cables and proper compressionless ones. I got the TRP cables and they've taken out all the sponginess that I had with Shimano Ultegra cables. They're not as good as full hydraulics, but are a lot closer in feel and power.

Gear cables are compressionless, standard brake cables aren't.

Wiggle do a load of cheap brake cables and outers.  Buy the lot.   My commuter bike gets new shifters, headset, BB, cables & outers, chains, cogs etc  every year.   Its not worth the clicking, grinding and clanking and I still spend less than a car or a metro ticket

All brake outers are compressionless - they wouldn't work very well otherwise.

Standard cables should be fine and 2500mm more than enough length for the outer. You can get a good estimate of the length by measuring your existing route with a tape measure.

The important thing is to ensure friction in the cable is minimised. So avoid any tight bends. If your brakes aren't returning properly excess friction is probably the reason, and too tight a bend the probable cause. So check your cable can move freely before you attach it to the brake.

Pads vary between different makes, so make sure you buy some which are advertised as compatible with your brakes.