Braking down
QI put a new brake master cylinder on my Corolla. Since then, the brakes are fine when I set off, but the pedal gradually gets harder the further I drive. After fifteen miles, the brakes are really hot. Is the new cylinder at fault?
Kevin White, Cumbernauld
AWe think the master cylinder’s being held ‘on’ slightly by the servo pushrod. This means the fluid can’t escape freely up into the reservoir as it heats up and expands. The fluid therefore starts to apply the brakes – thus heating and expanding further.
Unbolt the cylinder and pull it forward. Look for the servo pushrod length adjustment. There’s often a dome-headed nut or bolt. Back it off until there’s a clearance of 0.5 to 1.0mm between the pushrod and the master cylinder piston with the pedal at rest.
Press the cylinder against the servo and feel for an slight springiness as the piston is pushed in. Some designs are adjusted by adding shims between the servo and the cylinder.