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Views: 27 Author: Site Editor Publish Time: 2025-10-28 Origin: Site
Brake system judder is a common problem encountered by drivers. At the very least, it can affect driving comfort, while at the worst, it can indicate a decline in braking performance and even threaten driving safety. Many drivers experience regular vibrations in the steering wheel, pedals, or body of the vehicle when braking, but are unsure of the cause. This article will examine the core components of the brake system and provide a detailed analysis of the root causes of judder, helping drivers accurately diagnose the problem and address potential issues promptly.
As the core friction component of the braking system, the condition of the brake disc directly affects the braking stability. More than 90% of brake judder is related to brake disc abnormality, which is specifically manifested in the following three types of problems:
(1) Cause: When the vehicle frequently brakes suddenly (such as in congested urban roads) or continuously brakes on long downhill slopes (such as mountain roads), the brake disc temperature can instantly rise to more than 500℃. The metal expands unevenly due to heat, and it is easy to produce "thermal stress residue" after cooling, resulting in slight warping of the disc surface (flatness error exceeding 0.05mm will cause judder).
(2) Phenomenon: When the vehicle speed exceeds 60km/h and the brake is applied, the steering wheel or pedal will experience "periodic vibration". The higher the speed and the greater the braking force, the more obvious the judder; the judder disappears immediately after the brake is released.
(3) Verification method: After removing the wheel, use a dial indicator to check the flatness of the brake disc. If the pointer swings more than 0.05mm when rotating, thermal deformation can be confirmed.
(1) Causes:
Uneven hardness of the brake pad (low-quality brake pads contain too large metal particles), long-term friction causes grooves of varying depths (depth exceeding 0.5mm) on the surface of the brake disc;
Poor return of the brake caliper (such as rusting or jamming of the guide pin), causing the brake pad to contact one side of the brake disc for a long time, forming "step-shaped" eccentric wear (the difference in wear on both sides exceeds 1mm).
(2) Phenomenon: The vibration is slight when the brake is lightly pressed, and the vibration is aggravated when the brake is pressed hard, and may be accompanied by a "scratching" friction noise; in severe cases, obvious scratches can be seen on the surface of the brake disc.
(1) Material defects: Low-priced and low-quality brake discs are made of recycled cast iron, which have pores and impurities inside. After long-term use, they are prone to local cracking or "partial wear points", resulting in uneven friction force.
(2) Improper installation: The brake disc fixing screws are not tightened according to the specified torque (too loose or too tight), or the disc surface is knocked during disassembly and assembly, causing deformation. When braking, the disc surface shakes and causes vibration.
As a component that directly contacts the brake disc, the abnormal state of the brake pad can also cause brake vibration, which is mainly manifested in the following aspects:
(1) Uneven wear: The thickness difference of the brake pad on both sides exceeds 2mm (caused by uneven caliper pressure and unequal return spring elasticity). When braking, the friction on both sides is unbalanced, causing the brake disc to vibrate irregularly.
(2) High temperature hardening: Frequent braking causes the brake pad temperature to be too high (over 600°C), carbonizing the surface of the friction material to form a "hard shell", causing the friction coefficient to drop sharply and be unevenly distributed, resulting in alternating "slip-friction" vibrations during braking.
(1) Installation defects: The gap between the brake pad and the caliper is too large, or sand or metal debris is mixed in during assembly, which will produce "impact-type friction" during braking and cause high-frequency vibrations.
(2) Unqualified materials: The friction material of inferior brake pads (such as those containing asbestos or excessive impurities) is unevenly distributed, resulting in large fluctuations in the friction coefficient during braking, causing unstable force on the disc surface.
The brake calipers and hydraulic systems are responsible for converting pedal force into brake pad clamping force. Abnormalities in these systems can lead to uneven distribution of braking force, indirectly causing vibration:
(1) Caliper jamming: The caliper guide pins are lacking oil and rusting, and the piston seals are aging, which causes the brake pads to not fit evenly on the brake disc, resulting in "unilateral friction". During braking, the force offset causes vibration (often accompanied by vehicle deviation).
(2) Caliper fixation is loose: The caliper bracket screws are loose, and the caliper itself shakes during braking, causing the contact angle between the brake pads and the brake disc to continuously change, forming periodic vibration.
(1) Brake fluid problem: The brake fluid has too high a water content (over 3%) or is mixed with air, which can cause delayed and unstable brake pressure transmission, and the brake pad clamping force fluctuates, causing vibration.
(2) Master cylinder/slave cylinder failure: internal wear of the master cylinder and oil leakage of the slave cylinder will lead to insufficient braking force on one side of the wheel. When braking, the brake discs on both sides are unevenly stressed, resulting in vibration (often accompanied by soft braking).
In addition to the core brake components, abnormalities in the following related components may also cause brake vibration and need to be checked one by one:
(1) Wheel deformation: The wheel deforms slightly after being hit (such as when driving too fast on a bumpy road), causing the brake disc to rotate eccentrically with the wheel, and the friction track to shift during braking, causing vibration.
(2) Tire dynamic imbalance: The tire dynamic balance block falls off, and the wheel rotates eccentrically when driving at high speed. This imbalance will be amplified during braking, manifesting as vibration of the vehicle body or steering wheel (the vibration may still exist after releasing the brake).
Loose ball joints of suspension components such as the lower arm and steering rod will cause unstable force transmission to the vehicle body during braking, which will amplify the slight vibration of the brake disc into obvious vehicle body shaking, which is often mistaken for a "brake system problem".
(1) Shake only when braking: Focus on checking the brake disc, brake pads, and calipers (90% probability).
(2) Shake both when braking and not braking: Prioritize checking tire dynamic balance, wheel hub deformation, and suspension looseness.
(3) Accompanied by deviation: Mostly caused by caliper jamming, wheel cylinder failure, or brake pad wear.
Remove the wheel and visually inspect the brake disc surface for grooves, cracks, or wear;
Touch the brake pad with your hand to feel whether the thickness is uniform and whether the surface is hardened or peeling;
Shake the caliper to check for looseness; press the guide pin to determine whether it is stuck (normally it should be able to move flexibly).
Use a brake disc flatness tester to measure the flatness (errors exceeding 0.05mm require repair or replacement);
Use a brake pressure tester to detect the difference in braking force between the wheels on both sides (exceeding 15% is abnormal).
Although the root causes of brake system tremor are complex, the core is mostly concentrated in the three major components of the brake disc, brake pad, and caliper. In daily driving, you should avoid frequent sudden braking and continuous braking on long downhill slopes (to reduce thermal deformation of the brake disc), regularly check the thickness of the brake pad and the condition of the brake disc (it is recommended to check once every 20,000 kilometers), and replace the brake fluid according to the cycle (every 2 years or 40,000 kilometers).When you replace brake parts, it is also very important to choose high-performance and safe brake parts. Only by solving the problem from the root can we ensure braking safety and make every brake smooth and reliable.If you want to purchase durable and high-quality brake pads or other brake parts,you can visit our website:https://www.evfriction.com.If you want to order,you can call us by +86-13363216781 or email us by jessicabrakes12@gmail.com.
