Automotive brakes — effect of insufficient brake pedal free play When the brake pedal free play is adjusted to less than the manufacturer's specified value on a hydraulic brake system, what condition will most likely occur during normal driving?

Introduction / Context:
Brake pedal free play is the small initial movement of the pedal before the master cylinder pushrod begins to build hydraulic pressure. Proper free play allows the master cylinder ports to uncover and the system to fully release. This question tests practical understanding of brake adjustment and the consequences of incorrect settings in service workshops.

Given Data / Assumptions:

• Hydraulic service brakes with a vacuum/servo booster in a passenger car.
• Free play is less than the specified value (i.e., too little).
• System otherwise in normal condition (no sticking caliper, no contaminated fluid).

Concept / Approach:
When free play is too small, the master cylinder pushrod can slightly depress the primary piston at rest. This closes the compensating (replenishing) port, preventing pressure from fully venting back to the reservoir. Residual pressure remains in the lines, especially as temperature rises during driving, causing the pads/shoes to remain in light contact with the rotors/drums. The result is brake drag, heat buildup, accelerated wear, and poor fuel economy.

Step-by-Step Solution:

Verification / Alternative check:
Technicians often confirm by spinning a raised wheel: if rotation is stiff and improves after loosening the master cylinder pushrod or increasing pedal free play, drag due to incorrect adjustment is proven. Temperature checks show overheated wheels after a short drive.

Why Other Options Are Wrong:

• Brake fade: typically due to overheated linings after heavy braking, not primarily free play setting.
• Vapour lock: related to fluid boiling and gas formation under extreme heat, not small free play alone.
• ABS malfunction: ABS may trigger or modulate during drag, but insufficient free play is not a direct ABS fault source.
• Steering pull: can be a secondary symptom if one side drags more, but the primary effect is generalized drag.

Common Pitfalls:
Confusing the purpose of residual valves (in drum systems) with drag; misadjusting booster pushrod length; ignoring thermal expansion of fluid that worsens drag over distance.

Final Answer: