BEDDING IN NEW BRAKE SHOES
After relining Austin Seven brake shoes of the pre-Girling riveted type, it will often be found that the contact between lining and drum only takes place at a number of high spots on the linings. This is due to variations in lining thickness and the usual small wear and misalignments in the brake components. As a result, braking performance may initially be disappointing. If the brake cam bushes have been renewed and have no sideways slack, it is even possible for only one of the two linings in a given brake to be providing most of the braking. Depending on whether this is the leading or trailing one, the braking effort will be different and pulling to one side will be noticed. After several thousand miles of use the linings will of course bed in nicely and good braking will be restored, but this could represent years of motoring for some A7s! Ideally, linings would be turned to the correct arc to match the drum using a large lathe, but very few firms are equipped for this nowadays.
I have used an alternative method at home, originally suggested by the vintage motorcycle fraternity. The idea is to temporarily increase the friction of the swept area of the drum by lining it with glasspaper. You will need a strip 1” or 1.25” wide by 22” long. I used a roll of Mirka Hiomant 120 Grit aluminium oxide paper which is about 20 thou thick. The strip is carefully fitted inside the drum using thin double sided sticky tape or rubber cement. There should be no overlap at the joint, but a small gap won’t matter. With the appropriate corner of the car on axle stands, the drum is refitted to the brake and rotated by hand in its normal direction, whilst simultaneously applying the brake lightly by pulling down on the cable. Refitting the road wheel is optional, but gives the benefit of a flywheel effect. You will hear and feel dragging as the high spots are removed from the linings. After each few turns, remove the drum and check the appearance of the linings. I stopped at the point where about two-thirds of their area had a matt appearance.
Bear in mind that friction material is removed quite quickly, so don’t go too mad - keep checking frequently! This operation generates plenty of dust, which I later removed with a vacuum cleaner. I only recommend this method for asbestos free materials, for obvious reasons. To save time, one can use the same “treated” drum for all four brakes, but the perfectionist will want to use the individual drums in case they vary in diameter due to wear. The sandpaper is peeled off afterwards and any adhesive residue removed carefully with solvent. The improvement in braking is small, but with an A7 any improvement has to be worth the effort!