Bike Repair – Servicing Dual Pivot Brakes

Servicing Dual Pivot Brakes

The rigours of riding, particularly in the winter, are hard on your brakes. However, there are simple steps to keep them working efficiently, whatever conditions you ride in.

Modern brakes are very reliable and perform sufficiently well that it’s easy to think they are maintenance-free, but they do still need regular checks and, in particular, regular cleaning. Cable sets should be replaced every two to three years as the inner liner wears, and the inner cable alone should be replaced if it has become frayed.

Brake pads/shoes should be replaced when the grooves have worn away or the wear line is reached. Many modern bikes’ brakes have replaceable brake shoes. Brake cable outers are made from spiral wound steel with a plastic outer covering and a polythene liner and should be cut with side cutters. Cable cutters should be used to cut inner cables. Inner cables for use with drop-bar levers have a pear shaped nipple. Universal brake inners will come fitted with both a pear-shaped nipple and a barrel shaped one; simply cut off the barrel nipple.

There are three types of internally-run cables

  • Where there’s a small diameter tube for the inner wire to run inside the frame and the outer casing stops at the tube. The inner wire is simply fed through the small diameter inner tube and the outer casing cut to protect the exposed wire.
  • The outer cable runs right through the frame. Remove the outer cable first from the frame, leaving the inner cable still in place. Slide the new outer over the old inner and feed through the frame until it comes out the other end. The inner can then be replaced.
  • The inner wire runs bare through the frame with the outer casing simply stopping on the outside of the tube. Remove the outer from the brake end and slide a long piece of the thin liner from the outer casing over the old inner wire right through the frame before pulling the inner cable out. Slide the new inner wire through the new outer and extra piece of liner. Remove the extra piece of liner once the new inner wire is fully in place.

1. Brake pads and rims

Keeping your rims and brake pads clean is essential if your bike is used in wet weather. Wash the rims and pads with slightly soapy water to remove the dirt and grey aluminium oxide film; this will greatly improve brake efficiency. Remove embedded grit from the pads. Check the rims’ surfaces are not ridged or concave. If they are, investigate further or ask an expert. Rims can fail when worn, with serious consequences. Replace the brake pads well before they wear out completely.

2. Callipers, brake levers and cables

Check the inner brake cables are not frayed either inside the brake lever or at the calliper. Check the inner cable’s end cap has not fallen off; replace if needed. Apply a thin coating of anti-seize grease to the brake adjuster threads, which is a frequent point of seizure on bikes used in wet weather. Check that the calliper mounting bolts are tight, the caliper arms pivot smoothly, and both brake pads hit the rim evenly without rubbing the tyre or overlapping the edge of the rim’s braking surface. Check the brake levers are secure.

3. Cable trimming

It is important that the outer cable for the rear brake is not too short; check that the bars can be turned freely either way without tugging the outer cable. If okay, use the length of the existing cable as a guide to the length of new cable required. Use side cutters to cut between the spiral, making as clean a cut as possible. Use a small file to trim the end flat and then a small pointer to open the end of the liner. Fit the ferrule.

4. Cable fitting 1

Undo the inner cable at the calliper. Undo the top half of the handlebar tape. Remove the old brake cable, push the inner cable out through the brake lever. Slide the new inner cable through the brake lever body. Sometimes it may be necessary to remove the lever body from the bar before threading the inner cable through. Slide the first section of the outer cable over the inner cable and make certain that the cable with its ferrule fits tight up to the lever body. Tape the outer cable to the bars along the grooves if possible or along the front of the bar.

5. Cable fitting 2

Retape the bars. Feed the outer cable through the stops or guides. Ensure the quick-release is closed (with Shimano and SRAM these are on the calliper, Campagnolo’s is on the lever). Thread the inner cable through the cable-clamp and fasten approximately into place. Turn the brake cable adjuster about one turn anti-clockwise. Trim off the inner cable, leaving about 5cm beyond the clamp bolt. Slide a cable end cap over its end, hold in place and with side cutters gently crimp the cap three times. Don’t squeeze the side cutters too hard because it’s easy to slice through the cap.

6. Brake adjustment

Hold the brake blocks on the rims, pull the cable taut and tighten the clamp bolt. Pull hard on the brake several times. Check that the clearance between the brake pads and rim is about 2-3mm. If it is just a little more or less, use the cable adjuster to get it right. If it is a lot more, start from the beginning again by loosening the inner cable and pulling taut with the brake pads held against the rim. If just one brake pad is rubbing on the rim, you need to centre the brake caliper – see step 7.

7. Calliper centring

Both brake blocks should sit an equal distance from the rim after adjustment. If one brake block rubs the rim you’ll need to center the brake calliper. It’s best to use a thin open-ended spanner as shown. Where fitted, you can make micro adjustments to the grub screw on the calliper arm using an Allen key or crosshead screwdriver, grasp both calliper arms and twist the brake or loosen the calliper mounting bolt, reposition the calliper and then retighten.

8. Fitting new brake shoes

Undo the Allen nut/bolt securing each brake shoe and replace with the new shoe. It is vital that any open-ended shoe has the open end facing rearwards. Align the brake pads so they line up with the rim’s braking surface and do not touch the tyre or overlap the rim edge. With brakes that allow angular adjustment of the shoe, fit the conical washer on the inside and the plain washer on the outside. Slide a layer of card behind the rear edge of the brake pad, push the brake pad firmly against the rim and then tighten its mounting bolt firmly. The front edge of the brake pad should touch the rim 1mm or so before the rear edge.

9. Fitting new brake pads to old shoes

With the brake shoes still in the calliper, remove pad-retaining screws if fitted. Loosen the shoe mounting bolt and turn the shoe if necessary so that its open end faces outwards from the calliper. Retighten the mounting bolt and insert a screwdriver between the pad and the shoe, gently levering the front edge of the pad out of the shoe. Remove the brake shoe and pull the pad completely  out of the shoe. Slide the new pad into the shoe from the open end. If it’s tight use a little washing up liquid on the pad/shoe interface. Refit the shoe as described in step 8. Readjust the brakes as in step 6.

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