When you have to operate both front as rear brake but only can use one hand, a cable doubler/splitter comes in handy. For this you can perfectly use a splitter which mountainbikers use to lockout both front as rear suspension with one lever! Suspension manufacturer Fox produces such remote lockout splitters, for example the “Fox 2014 – 2017 AM Splitter”:
One cable runs from the brake lever through the splitter, directly to the front brake. The other cable runs from the splitter to the rear brake. This provides a 100% safe connection.
The Problem Solvers Cable Doubler is a very, very dangerous solution!
The pulling cable doesn’t run through the splitter but is secured with a very tiny bolt inside the splitter. So, when this comes loose, you’re out of brakes! Despite of perfect maintenance this happened to us, so we know what we’re talking about. Fortunately it happened at very low speed, with no traffic or other obstacles on the road. Otherwise this could have caused severe injury or even death…
Because you are pulling two brakes, you need a little more pressure when sqeezing your brake lever. So you want to use cables with as low friction as possible. Therefor you can best use coated cables such as the Shimano coated brake cables.