Cause of grabbing brakes

[Alastair Gill]

I had a problem with rear off side brake grabbing on when moving at slow speed either forwards or backwards. In addition there was a “metallic clunk” noise as if a brake shoe was hitting the back plate.

When travelling at speed, providing I had “test” applied the brakes in a safe place when setting out, I found there seemed to be no problem of grabbing.

I did the usual things of filing the leading and trailing edges of the brake lining - a gentle slope for the first half inch either end of the brake lining. Also gently filed off the sharp edge of the brake lining.

Checked various dimensions to see what might be causing the shoe to rock over and hit the back plate

Ultimately after extensive detective work, I noticed that there was a bright metal rub line running around inside the brake drum at the edge of the rubbing face furthest from the back plate. I noticed that the brake lining hung over the edge of the shoe a tad on the side furthest away from the back plate. Filed it back the brake lining to be flush with the brake shoe. Cured !  No more grabbing of brakes and no “metallic clunk” of the shoe hitting the back plate.