What is the reason why newly replaced brake pads cannot stop the car?

[SanCamilla]

Newly replaced brake pads cannot stop the car because the surface of the new brake pads is relatively flat, while the contact surface on the brake disc is very uneven. This results in a very small contact area between them. Due to the insufficient contact area, enough braking force cannot be generated, so the car cannot be stopped. Braking is achieved through intense friction between the brake pads and the brake drum. When driving in water, the wheels are almost submerged, leaving a layer of water film between the brake pads and the brake drum, similar to applying lubricant. This reduces the friction between the brake pads and the brake drum, making it impossible to control the car to stop, and the water inside the drum is not easily dispersed. After leaving the water, stepping on the brakes several times while driving will wipe away the water droplets between the brake pads and the brake drum. At the same time, the heat generated by friction will dry them, quickly restoring the original sensitivity of the brakes.

[PaigeLynn]

New brake pads not working properly? I just helped a neighbor diagnose a similar issue last week. There are mainly three potential problems: First, you might have installed inferior brake pads with friction material that's too hard or contaminated with oil. A mechanic mentioned that aftermarket parts may have 10% lower friction coefficient than OEM parts, especially noticeable during hard braking at high speeds. Second, improper installation - unlubricated caliper guide pins causing poor retraction, resulting in partially engaged brakes over dozens of kilometers, leaving blue spots on the rotors. Third, air in the brake lines due to improper bleeding procedure, making the pedal feel spongy. I recommend first checking for oil stains near the tires, then going through a break-in period. Normal pads need to wear off the surface layer (about 300km of gentle braking) to reach optimal performance. Don't rush to replace components - many vehicles improve significantly after proper break-in.

[DelilahDella]

As a DIY car maintenance enthusiast, I've encountered poor performance issues with new brake pads, primarily due to overlooked installation details: failing to clean the contact surface of the brake disc during installation, leading to slippage caused by oil stains or rust; forgetting to reinstall the anti-vibration shims on the caliper bracket, resulting in metallic clanking sounds during braking and impaired stopping power; additionally, not chamfering the brake pads caused their edges to bite into the brake disc. I recall one instance after replacing the pads where the stopping distance from 60km/h increased by two car lengths compared to before. Later, it was discovered that the guide pin rubber boot had aged and seized—replacing it with a new one costing just 30 yuan solved the issue. I recommend focusing on checking these details, as they're more critical than simply switching to a different brand.

[SanAllison]

From an automotive engineer's perspective, the core issue of new brake pad failure lies in insufficient compatibility between friction materials and system matching. Replacing standard pads with racing-grade metal-ceramic compounds in family cars requires higher operating temperatures that normal driving can't achieve. Experimental data shows NAO material pads achieve 0.38 friction coefficient at 100°C, while ceramic pads require 300°C to reach 0.4. Additionally, worn brake discs with over 0.5mm lip height reduce new pad contact area by 40%, necessitating simultaneous disc resurfacing. Brake master cylinder compensation port blockage causing slow hydraulic pressure buildup may make new pads perform worse than worn ones. Always conduct brake temperature testing with monitoring during modifications.

[JeffreyAnn]

Friends at the repair shop encounter these common pitfalls every day: First, the old brake discs already have grooves, preventing the new pads from fitting properly, resulting in squeaking sounds; second, the sliding pins are over-tightened during assembly, causing uneven clamping of the brake pads; third, the sensor plug is not reset, triggering false ABS activation. It's recommended to first check if the steering wheel shakes when braking—if it does, the discs need resurfacing. Also, inspect the tire surface for localized wear patches, which indicate uneven braking force. Additionally, avoid sudden braking for the first 300 kilometers after replacement, as high temperatures can vitrify the surface of the friction material, making it as slippery as ice.

[OLyla]

With 15 years of mechanical experience, most braking failures stem from hydraulic system issues. Last week, a Passat had soft brakes after pad replacement—testing revealed the old brake fluid had over 5% water content, forming vapor locks when heated during bleeding. Another case involved an Excelle’s ABS pump accidentally triggered during pad replacement, requiring OBD reset. Focus on three key points: 1. Post-pad replacement, 20 brake pedal pumps are needed to eliminate piston clearance—often skipped; 2. Check if excessive wheel hub bearing clearance causes rotor wobble; 3. Mixing brake pad brands can lead to friction material conflicts. Prioritize diagnosing these hidden issues before rushing into part replacements.