Technical advice: Fixing radial play in brake discs

MCN expert Chris Dabbs is here to answer any questions you have on anything bike related.

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Q. Although my Brembo fully floating cast discs sound like a bucket of scrap when the bike is wheeled around, they still work as they should.

But there appears to be a little bit of radial play in them which did not impress my MOT man. I have searched the net for info or to see if I can find someone to overhaul these discs with no success.

All I can find is a source for bobbins. Are the bobbins made of a softer alloy than the centres and would a new set of bobbins sort them out or are the centres likely to need replacing as well?

Dell, e-mail

A. The bobbins are actually harder than the centres, which are known as “bells”, but you should be able to tune out any wear with shims that you can fix either side of the bobbins.

These shims cost the princely sum of 18p each from GPR Developments in Silverstone (01327-855585) and are 0.2mm thick.

Check which ones are rattling, then unbolt the discs from the removed wheels for ease of access, flick off the e-clip and slide a shim in place until Mr. MOT will be happy.

Make sure you torque the disc carrier bolts up correctly (generally about 18ftlb for M8 bolts). You can use a locking agent, but some paint, say from a tyre marker pen, dabbed on the bolt and the bell will let you tell at a glance if the bolt is coming loose.