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Haynes Workshop: Burgman 250/400 brake discs

CHECKING FOR WEAR

Inspect the disc surface for score marks and other damage (photo 1).

Light scratches are normal after use and won’t affect brake operation, but deep grooves and heavy score marks will reduce braking efficiency and accelerate pad wear. If a disc is badly grooved it must be renewed. The disc must not be allowed to wear too thin – a minimum thickness specification is stamped into the disc surface (photo 2). Measure the thickness of the disc in the brake pad contact area with a micrometer (photo 3). Fit a new disc if necessary.

If no measuring equipment is available, check for a ridge between the disc rim and the pad contact area and renew the disc as necessary.

CHECKING FOR DISTORTION

If the disc is running out of true, the lever will pulse when the brake is applied.

To check front disc distortion (run-out), support the scooter on its centrestand with the front wheel raised off the ground. Attach a dial gauge to the front suspension with the gauge pointer touching the surface of the disc close to the outer edge (but clear of any drilled holes). Rotate the wheel slowly and watch the gauge needle, noting the maximum run-out.

When checking rear disc run-out, attach the dial gauge to the transmission casing or the rear sub-frame, depending on the method of disc mounting.

The manufacturer will specify a service limit (maximum) for disc run-out (0.3mm in the case of Burgman models). A run-out reading beyond this indicates that the disc is warped. Check first that the disc mounting bolts are secure and that the problem isn’t due to worn wheel bearings.

CHANGING A FRONT DISC

When renewing a front disc, start by removing the front wheel. Unscrew the disc retaining bolts, loosening them evenly, a little at a time; then remove the disc.

Before installing the new disc, make sure there’s no dirt or corrosion where it seats on the wheel. If the disc doesn’t sit flat when bolted down, it will appear to be warped when checked, or when the brake is used.

Remove any protective coating from the working surfaces of the new disc. Install the new disc on the wheel with its marked side facing out. Clean the threads of the retaining bolts and apply a suitable non-permanent thread-locking compound, then install the bolts and tighten them evenly; if the manufacturer specifies a torque setting for the disc bolts make sure you use it.