LPB Brake Pads
Common Issues and Solutions for the Brake System
1. Loss of braking efficiency (vapour lock)
What is a brake fluid?
Brake fluid – a mixture of synthetic organic chemicals – transmits hydraulic pressure from the brake pedal through hydraulic lines to the braking mechanism near the wheels. To make this possible, brake fluid must be incompressible.
Vapour lock of brake fluid
Braking generates considerable heat. To resist these high temperatures without boiling, brake fluid is designed with a high boiling point. But brake fluid is also hygroscopic, which means it absorbs water. In any hydraulic brake system, the brake fluid gradually absorbs moisture from the air through the flexible brake hoses or the reservoir breather. This moisture reduces the brake fluid’s boiling point.
Once this moisture absorption reaches a certain level – under prolonged, hard braking, especially when the vehicle is heavily loaded – the generated heat can cause the brake fluid to start to boil, creating gas bubbles. As gas is far more compressible than liquid, the driver will experience no pressure at all on the brake pedal, resulting in a complete loss of brake power. This is known as the vapour lock.
What can we do to prevent the vapour lock?
Check brake fluid regularly.
Replace brake fluid after 40,000 km or at least every 2 years.
Brake fluid of different DOT is not allowed to mix.
Description: Brake fade (scorched)
Cause: Heat fade because of brake system abuse
Solution: Replace the brake pads.
Good braking habit.
Description: Low brake fluid level/brake fluid leaks/damage of brake hose
Cause: Limited hydraulic pressure in brake hose.
Solution: Add the brake fluid of same DOT.
Replace the broken brake hose.
Description: Grease of brake pad.
Cause: Friction material is polluted by oily substance.
Solution: Replace the greased pads.
Clean the oily substance on disc.
Description: Abnormal wear of tire.
Cause: Low/excessive tire pressure, incorrect dynamic balance of tire.
Solution: Adjustment of tire pressure, and replace the tire if necessary.
Description: Inadequate contact between pad-disc.
Cause: Worn or incorrect brake disc, fitting faults
Solution: Replace both pads and discs.
Description: Vehicle overload.
Cause: Vehicle overload lead to the increase of vehicle’s kinetic energy, which could increase the stopping distance.
Solution: Prevent the overload of vehicle.
2. Brake noise
Influence factor of low frequency noise - Brake system
Un-parallel of brake disc-caliper due to incorrect assembly
Sticky movement of the caliper piston and/or the sliding parts of caliper
Poor roughness of the working surface of disc-pads
Raised borders on upper and lower edges of brake disc due to the smaller friction area of last brake pads
Shim fall off or disable due to incorrect assembly
3. Brake judder
Influence factor of a brake judder
Run-out error between the supporting and the braking surfaces
Cause 1: Hub and/or Disc Runout
Poor machine accuracy of brake disc
Poor installation of brake discs and wheel hub
The above two situation can induce the un-parallel of brake disc and wheel hub/caliper. And when the runout is larger than allowed value (generally, 0.03-0.07mm), it can result in the brake judder.
Error in the parallelism of the braking surfaces
Cause 2: Disc Thickness Variation (DTV)
DTV is the variation in thickness around the disc surface. For effective braking, the disc should have the same thickness throughout. But DTV indicates unevenness on the friction surface of the disc.
When the DTV is larger than the allowed value (generally, 0.025mm), the brake pad loses and regains contact with the disc(s) as it turns. And that’s what causes
4. Abnormal wear of brake pads and discs
Brake problems are related to the steering system, driving system and braking system of vehicle and the mechanism is complex. Some problems are not simply caused by brake pad / disc, but the result of mutual coupling and excitation between vehicle components.
Brake problem should be considered from the point of systemic view and comprehensive, and the related parts and its working state should be carefully checked.