Shimano has confirmed to 220 Triathlon that around 930 mechanical disc brakes for road bikes are believed to be affected in the UK by a product recall that it sent out last week.
Asked to describe the exact nature of the problem, a spokesperson said: "When adjusting the brake pads wrong it was possible that the pistons didn't work 100%."
The problem was discovered by a member of a sponsored cyclocross team; no injuries have yet been reported.
Shimano has confirmed that it will be replacing affected units free of charge with improved ones that do not suffer the same issue.
The disc brakes affected are models BR-CX75, BR-R515 and BR-R315, sold after February 2012.