Monday maintenance: Cable discs - Bike Magic

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Monday maintenance: Cable discs

Hurrah for the simplicity and easy maintenance of cable disc brakes the propaganda says. Well that is until you use the damn things.We’ll admit that some recent brakes such as Hayes and Avid do seem to live happy and totally fulfilled lives without screaming for attention all the time. However, this week we’re looking at the ways to get the best from earlier generation – or just plain cheap – cable disc brakes that come fitted as standard on many ‘lower end’ bikes.

Set up
It’s all in the angle of dangle.

Cable disc brakes work by using a standard cable to pull a lever arm that attaches to a spindle running on a spiral thread through the caliper. On the far end of this spindle is the brake pad. By pulling the lever arm, you turn the spindle which screws it along the thread to push the pad onto the rotor to stop you. It’s a simple system that’s been used for years (first by Shimano and then Hope) but it needs to be set up right to work properly.

The crucial part of setting up depends on the lever arm. While some enlightened companies (Shimano, Avid, Hayes) have used a small cam on the end of the lever arm to pull give constant leverage on the cable, others just use a simple straight arm and direct cable pull. This means that the lever arm has to be perpendicular to the cable stop on the caliper at the point of pad – rotor contact to ensure maximum power. A few degrees either way can mean the difference between decent braking and none at all, so be very careful how you set the brake up to start with.

Well adjusted

Unlike self-adjusting hydraulic systems cable brakes also need to have their pad wear compensated for manually. If you’ve got a cam arm brake, then the cable adjuster on the brake lever can be used to take up slack, but without a cam, the leverage of the arm and therefore braking power will fall as the pads wear. This means you need to adjust the pad spacing at the caliper to keep control.

How often and how much depends on your braking and pad life in current conditions, but we’ve gone from working discs to levers to the bar without any hint of braking in the space of a relatively short downhill before. If in doubt, check and adjust as often as you can.

Grind and bind

Cable brakes are also vulnerable to grit and cable stiffness affecting control in the same way as V brakes are. For a start the lengths of cable are very long, and though continuous outer cable sections are better sealed than several short pieces, they are much harder to clean once they get gritty. Long cables also means more stretch of the inner wire / compression of the outer and more length for friction to build up in, which means a less direct feel at the lever. Besides regular cleaning there’s not much you can do, although Avid’s “Full Metal Jacket” upgrade (Raw 0131 440 2010) improves feel be replacing the last length of cable outer on the seatstay with a piece of thin steel pipe.

The cable has to pull a lever smoothly though a coarse screw thread, against the pressure of the big spring needed to pull the pads back off the rotor. While Hayes, Avid and Shimano use decent bearings (at a weight penalty) other brakes need stripping, cleaning and greasing regularly to keep responses smooth and controlled. Be careful that big spring doesn’t fire the guts of the brake into the far corners of the room as soon as you try and strip it down though. We generally try and keep a firm hand or rag wrapped round the whole assembly as we undo the main retaining bolts.

On the bright side there are no corrosive hydraulic fluids to spill everywhere.

Next Week

As we’ve already covered basic bouncing and stopping we’ll probably be doing something about getting your bike going along smoothly. Or we might just run a feature on how best to sell those cheap cable disc brakes that came with your bike and buy some proper hydraulics instead (though we’ll let you off if you’ve got Hayes or Avid).


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