In today’s high-speed world, our vehicles are crucial. So if they start to misbehave, we get worried. Few things bother me more than feeling a jerky motion in the brake pedal while stopping, slowing, or when we’re actually at a stop, unless you want a repeat experience!
Join us as we look at what could cause this annoying problem, whether you are braking or coasting to a stop, or when you are actually stopped, because we don’t want to do that again.
Causes of a Car That Jerks When Braking
While many drivers will experience that “jerking” response, it’s not all that common. That said, it is common enough to cause alarm and indicate there is a problem that needs solving.
Here are several of the most common reasons that a vehicle jerks when the brake pedal is pressed.
#1. Warped Rotors.
Warped brake rotors are the leading cause of a jerking feeling when a vehicle’s brakes are applied. Over time, a vehicle’s brake rotors can be warped due to overheating, wear, or sudden cooling.
This warp is felt as the vehicle’s brake pads are pressed against the affected brake rotors, producing an obvious pulsing.
#2. ABS Actuation.
The actuation of a vehicle’s anti-lock braking system (ABS) valve will produce an obvious jerk while stopping.
If you have ever attempted to stop suddenly (especially in the rain), this should be no cause for concern; however, if the vehicle’s ABS system begins actuating during every stop, investigation is warranted.
#3. Compromised Brake Booster
Another very possible reason for a vehicle to shake while braking is a faulty vacuum-assist brake booster.
A vehicle’s brake booster operates by manipulating a diaphragm under a vacuum created while the brake pedal is pushed. If this diaphragm is compromised, a shuttering may occur during brake pressure.
#4. Seized Brake Caliper.
A majorly seized brake caliper can also cause a vehicle to jerk as brakes are engaged, making sudden jerks and jumps as a result of the binding that takes place from the vehicle’s brake pads being pressed on the rotors. This condition may also result in an audible chattering sound.
#5. Worn Steering/Suspension Bushings.
Your regular car uses many different bushings (control arm bushings, shock absorber bushings, steering rack bushings, etc.) to help with the absorption of vibrations in the vehicle’s front end.
These bushings tend to wear, allowing otherwise unnoticeable vibrations to be felt. The condition is expressed most frequently during braking.
Causes of a Car That Jerks When Slowing Down
A vehicle will jerk while slowing down, even when no defined brake application is present. The cause of this odd vibration should be duly isolated and fixed at the first opportunity. Here are a few of the most common reasons that a vehicle jerks when slowing to a stop.
#6. Transmission Problems.
A “jerking” feeling while slowing down to stop often indicates a transmission-related issue such as a bad valve body or TCM.
This tends to be true of both manuals and automatics, as both attempt to control their gearing and speed relative to the situation. Further diagnostics will be required to fully find the extent of this problem.
#7. Bad MAF Sensor.
It’s also rather common for a faulty Mass Airflow Sensor (MAF) to be the cause of the jerk as a car slows down. The Mass Airflow Sensor is how car relays feedback to an engine’s ECM/PCM of how much air is flowing into the intake tract.
This feedback helps to calculate the fuel trims of an engine. Erroneous feedback can lead to combustion irregularities.
#8. Ignition Coils.
While your ignition coils deliver precise sparks to each cylinder, as these coils begin to fail, it can lead to pretty much the same erratic “misses” at low speeds, or as we’ve come to know them, the bucking or jumping-type of behavior.
This can affect a car as well while cruising at high speed, but if often far more pronounced during mild acceleration, as the relative load on the engine is more pronounced in this circumstance.
#9. Sticky Throttle Body.
In some cases, a degree of “jerking” can be present if an engine’s throttle body is sticking. The throttle body meters all of the incoming air for the purpose of combustion introduced to an engine’s intake manifold, and if it “sticks”, or otherwise fails to actuate to where it is needed to meet the demand of the engine, a sort of hesitation is there.
#10. Vacuum Leaks.
Another common cause of a vehicle jerking down when reduced speed is also from serious vacuum leaks.
Not surprisingly, an older vehicle relied on engine vacuum to facilitate some critical functions, such as EGR operation, for example.
A leak within a vehicle’s vacuum system can cause bad, but erratic, misfire-type symptoms. Not where you feel it until you slow down to an eventual stop.
Causes of a Car That Jerks When Stopped
Although this is not the most common scenario, a vehicle can certainly jerk while sitting at a stop. This is a very alarming scenario to many, and can create a certain amount of anxiety before being resolved.
The following are several of the most common reasons that a vehicle jerks while sitting at a complete stop.
#11. Ignition System Issues.
A case of jerkiness or shaking when stopped at a light and idling could fall into the category of ignition problems. Worn spark plugs, aging spark plug wires, and/or faulty coil packs are common culprits here.
In older vehicles, an old/damaged distributor cap or rotor button was often the culprit in cases of a similar nature to those mentioned above.
#12. Fuel Delivery Problems.
When a miss is detected at idle, the reason often lies within the vehicle’s fuel system. A vehicle may suffer from a clogged fuel filter, defective fuel pressure regulator, or malfunctioning injectors.
The bulk of these issues seems easiest to detect when idling in a parking lot, or having stopped at a light.
#13. Inefficient Air Delivery.
An internal combustion engine must have a ready supply of clean air for intake at all times. If an engine is starved for air, combustion is not nearly as efficient, resulting in an extreme misfire.
This can be felt very easily while idling or at low load. The cause of problems of this sort is often traceable to defects in the throttle body, or the long-term usage of a clogged air filter.
#14. Vacuum Leaks.
Vacuum leaks are among the top complaints of erratic idle, as they let unmetered air into the engine’s intake tract, causing the ECM/PCM not to account for the operation of the sensor.
The engine consequently runs so lean, combustion efficiency suffers badly, and performance drops like a rocket.