What Causes the Lack of Braking Force in the First Half of the Brake Pedal Travel?
3 Answers
The lack of braking force in the first half of the brake pedal travel can be attributed to insufficient brake fluid pressure (due to low fluid level in the master cylinder, ruptured brake lines, leaking pipe connections, or clogged fluid passages), air in the brake system, excessive free play in the brake pedal or excessive brake clearance, poor contact or severe wear of the brake shoe friction lining, or oil contamination. Other causes include wear or scoring of the master cylinder, wheel cylinder pistons, or cylinder bores, as well as aging or damage to the rubber seals. Below is more relevant information: Vehicle Braking: Vehicle braking refers to the act of stopping the vehicle, where braking force is the maximum rolling friction achievable. This is because friction drops suddenly when rolling transitions to sliding—maximum rolling friction is greater than sliding friction. This is why vehicles are equipped with anti-lock braking systems (ABS). Braking performance is one of the primary characteristics of a vehicle, directly related to driving safety.
A while ago, my car had the same issue—the first half of the brake pedal felt spongy, and the speed barely decreased. Later, the mechanic diagnosed three common problems: first, air got into the brake lines, which usually happens after a brake fluid change—the first half of the pedal stroke is just compressing the air; second, the master cylinder’s seals were worn and leaking, so the pressure you applied was lost; and third, the brake pads might have worn too thin, causing the piston’s travel to lengthen. I’d suggest checking the brake fluid level first—if it’s dark, replace it. Then inspect the brake pad thickness—if it’s thinner than a coin, replace them. If you can’t handle it yourself, take it to a professional shop ASAP—brake issues shouldn’t be delayed.
My old car just got fixed for this issue - the first half of the brake pedal felt like stepping on cotton. The mechanic said it might be due to a stuck brake caliper where the piston wouldn't retract, causing no response when pressed. Also, brake fluid with too much water content can cause this by creating vapor lock at high temperatures, which is common in cars that are five or six years old. And if the adjuster arm in drum brakes fails, it's even worse - you get zero braking in the first half of pedal travel. In my case, changing the brake fluid solved the problem, and now the pedal feels crisp. Remember to check that the caliper pistons move freely during inspection, and use a water content tester on the brake fluid - if it's over 5%, it needs replacement.
