Our vehicles are vital in today’s fast-paced world. So when they act up, it’s concerning. Few things alarm more than unexpected jerking when braking, slowing, or stopped.
Let’s explore the potential reasons behind this unnerving issue, broken down by whether you’re applying the brakes, coasting to a stop, or when you’re actually sitting at a stop because nobody wants to experience that again.
Causes of a Car That Jerks When Braking
It is not uncommon for motorists to feel a “jerking” sensation when braking. While such issues are far from rare, they do require ample attention, in order to remedy the situation at hand.
The following are several of the most common reasons that a vehicle jerks when its brake pedal is depressed.
#1 – Warped Rotors
Warped brake rotors are the number one cause of a jerking sensation when applying a vehicle’s brakes. With time, a vehicle’s brake rotors can become distorted due to overheating, excessive wear, or rapid cooling.
This distortion is felt as a vehicle’s brake pads press against the affected brake rotors, causing a noticeable pulsation.
See Also: Replace vs Resurface Rotors
#2 – ABS Actuation
The actuation of a vehicle’s ABS (Anti-Lock Braking System) valve will cause a substantial jerking sensation when coming to a stop.
If you have attempted to stop abruptly, especially in wet conditions, this effect is nothing to be alarmed by. However, if your vehicle’s ABS system begins actuating at random stops, further diagnosis will be required.
#3 – Compromised Brake Booster
A faulty vacuum-assist brake booster is another likely cause of vehicle vibration when braking.
A vehicle’s brake booster operates by manipulating a diaphragm under vacuum when a vehicle’s brake pedal is applied. If this diaphragm is compromised in any manner, a shuttering may present itself during brake applications.
#4 – Seized Brake Caliper
A severely seized brake caliper can also cause a vehicle to jerk when applying the brakes. These jolts and jumps result from the binding that takes place, as a vehicle’s brake pads are wedged against its corresponding rotors.
In a number of cases, this condition is also accompanied by an audible chattering noise.
#5 – Worn Steering/Suspension Bushings
The typical vehicle utilizes many different bushings (ie: control arm bushings, shock absorber bushings, steering rack bushings, etc.) to dampen vibration within a vehicle’s front end.
However, these bushings do tend to wear with time, causing a noticeable increase in otherwise muted vibrations. This condition tends to express itself most prevalently during braking.
Causes of a Car That Jerks When Slowing Down
A vehicle can also jerk when slowing down, even in the absence of a defined brake application. The cause of this unusual vibration should be isolated and repaired, as soon as it is practical to do so.
The following are several of the most common reasons that a vehicle jerks when slowing to a stop.
#6 – Transmission Issues
This tends to be true of both automatic and manual transmissions, as they attempt to regulate their gearing and speed to the situation at hand. Further diagnostics will be required to uncover the full extent of such issues.
#7 – Faulty MAF Sensor
It is not uncommon for a faulty Mass Airflow Sensor (MAF) to cause an engine to jerk as a vehicle slows. A Mass Airflow Sensor provides an engine’s ECM/PCM with feedback pertaining to the amount of air flowing through the intake tract.
This feedback is used to calculate an engine’s fuel trims in real time. However, the presentation of inaccurate data can cause combustion irregularities.
#8 – Compromised Ignition Coils
An engine’s ignition coils provide a well-timed spark to each particular cylinder. However, as an ignition coil begins to fail, it often leads to the misfires at low speeds, which are often felt as bucking or jumping.
While such issues can also arise while cruising at high speeds, the jerking is far more prevalent during acceleration, as relative engine load is significantly reduced.
#9 – Sticking Throttle Body
In certain instances, a certain degree of jerking can occur when an engine’s throttle body begins to stick. The throttle body serves as the metering device for all incoming air introduced into an engine’s intake manifold for combustion.
If a throttle body sticks, or otherwise fails to actuate to the desired position to meet engine demand, a hesitation of sorts often comes as the result.
#10 – Vacuum Leaks
Yet another common cause of vehicle jerking during slow down is pronounced vacuum leaks.
An older vehicle often relied upon engine vacuum to facilitate a number of critical functions, including EGR operation. Worse yet, a leak within a vehicle’s vacuum system can lead to severe, yet erratic, misfires, which are often only felt when slowing to an eventual stop.
Causes of a Car That Jerks When Stopped
Though less common than the conditions described above, a vehicle can also jerk noticeably when sitting at a stop. For many, this is a cause for alarm and can cause a certain amount of anxiety until remedied.
The following are several of the most common reasons that a vehicle jerks while sitting at a complete stop.
#11 – Ignition System Issues
A jerking or shaking felt at idle, when stopped at a light, can often be attributed to one or more ignition system issues. Some of the most common of these issues include worn spark plugs, aging spark plug wires, and faulty coil packs.
In older vehicles, a worn or damaged distributor cap or rotor button were often to blame for issues of this general type.
#12 – Fuel Delivery Problems
A miss detected while idling is often caused by an issue within an engine’s fuel system. A vehicle can experience a host of fuel system-related issues, including a clogged fuel filter, defective fuel pressure regulator, or malfunctioning injectors.
The bulk of these issues seem to be most easily noticed when sitting idle in a parking lot, or at a stop light.
#13 – Inefficient Air Delivery
An internal combustion engine requires a steady supply of clean intake air at all times, to facilitate proper operation. If an engine is starved for air at any point, combustion efficiency and overall performance plummet, typically causing a severe misfire.
This misfire can be easily detected at idle, or during periods of low engine load. Problems of this nature can be attributed to throttle body defects or the prolonged use of a dirty or clogged air filter.
#14 – Vacuum Leaks
Vacuum leaks are among the most common causes of erratic idle, due to their allowance of unmetered air into an engine’s intake tract. This air is not accounted for by an engine’s ECM/PCM, therefore leading to a notably lean condition.
As a result, combustion efficiency is significantly stifled, and engine performance takes a nosedive of unmatched proportions.
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