If you feel your vehicle shaking, knocking, or making weird clunking noises while decelerating, you must address the issue and fix it as soon as possible. But first, you should know why the car jerks when slowing down and which component of the car is responsible.
For automatic transmissions, the reason can be faulty Mass Air Flow Meter (MAF) sensors, failing transmission, worn out clutch, moisture buildup, clogged fluid path and injectors, bad throttle position sensor, damaged coil packs, etc.
As for manual transmissions, bad clutch, worn gear, or insufficient transmission fluid.
Let’s get into the core of each problem and find out why your car jerks while braking at low speed or slowing down.
Car Jerks When Braking at Low Speed: 9 Possible Causes
As the jerking at low speeds issue is mainly related to the transmission, the reasons are mostly different for automatic and manual transmission. Here are the possible causes why your automatic or manual car might jerk while braking:
Automatic Transmission Issues
Unfortunately, cars with automatic transmissions are more likely to face this problem while driving at low speeds. The inner components of the transmission or weather conditions are the main culprits here.
Let’s find out what causes things to go wrong.
MAF Meter Damage
A crucial component of the fuel injection system, the MAF or Mass Air Flow meter, decides how much air will go into the engine to be mixed with the fuel. It sends necessary feedback to the engine PCM for the proper mix.
If something goes wrong with the MAF sensor, it won’t be able to calculate the right amount of air, causing irregular combustion in the engine. Hence, your vehicle starts jerking when you slow it down.
An automatic transmission is a complex part of your car with several moving components. The transmission ensures that you can smoothly shift gears while driving at any speed.
Components inside the transmission often wear out or get damaged. As a result, your vehicle makes a knocking noise when braking. Typically, the torque converter is the key component responsible for jerking and shaking while decelerating.
This mechanical device separates your car’s transmission from its engine to disconnect the drive wheels. Hence, the driver can switch gears without any resistance.
Usually, most car manufacturers recommend changing the clutch every 150,000 miles. Once you’ve passed this standard distance, the clutch will wear out, making the shaky car while slowing down.
If the car jerks only when driving at a low gear ratio and goes away as the gear ratio increases, it’s a sign that your clutch has worn out and needs replacement.
During a foggy or rainy night, moisture often forms inside your car’s distributor cap. As a result, electric signal arcs inside the component, causing the engine to misfire.
Hence, the engine will produce uneven power, and your car will jerk whenever you hit 25mph or any lower speed level. You can easily avoid this problem by parking your car indoors if there’s rain or dense fog at night.
Clogged Fluid Filters and Injectors
As you might know, the fluid filters on your vehicle separate dirt from the transmission fluid. Over time, the filters get clogged and require replacement. If you change the filters timely, it will prevent your vehicle from rattling when you shift gears and press the brake.
Also, you’ll hear a clunking noise when braking when the filters get blocked. Similarly, the fuel injectors on your vehicle often get clogged due to constant combustion inside the engine. Hence, there will be a fuel imbalance inside the engine, and it will surge and jerk.
If the fuel injectors are clogged, you’ll experience rough engine idles, difficulty starting, bad gas mileage, and trouble during acceleration.
Bad Throttle Body
Simply put, the throttle body controls the airflow system of your car. It ensures only the necessary air is mixed with the fuel.
So, a bad or faulty throttle body won’t be able to control the air supply causing idling and jerking at lower speeds. Apart from that, damage to the throttle position sensor will also lead to the same consequences as it monitors the throttle position and air intake of the engine.
Damaged Coil Packs
In more recent vehicles, the distributor is replaced by a set of ignition coil packs to create sparks for the engine cylinders. If the coil packs get damaged, there won’t be enough spark for combustion.
As a result, the engine will misfire, and the car will shake during deceleration. Changing the coil packs will help you easily get rid of this problem.
Manual Transmission Issues
In the case of a manual transmission, the issues are directly related to the gear system and the transmission. Luckily, these issues are easier to detect and solve. Here’s what causes a manual vehicle to bounce at low speeds:
Insufficient Transmission Fluid
You already know that most car bouncing issues are related to the transmission components, which initiate downshifting when you slow the vehicle. The transmission fluid ensures that all the components are lubricated and working optimally.
For this, you must maintain a standard transmission fluid level. A leak in the transmission system can cause insufficient transmission fluid levels and hamper the system. Besides, bad or old transmission fluid won’t be able to prevent friction between the moving parts.
Hence, the transmission might fail and make your car bounce when you reduce speed. You can check the undercarriage of the vehicle for leaks. A leak must be fixed if there’s any pinkish or red fluid on the floor.
Your car gears are responsible for speed and power control. The gearbox multiplies torque and transmits power to your drive wheels.
Naturally, the vehicle won’t remain stable at lower speeds if the gearbox is worn out.
So, there you have all the reasons why car jerks when slowing down. As you can see, the reasons are many and often varies in automatic and manual transmissions.
In some rare cases, a blown turbo, worn-out engine mounts, damaged brake booster, vacuum pipe leaks, warped rotors, etc., can also be why your car bounces during deceleration.
We recommend going to an expert to find out the damaged component and repair or replace it without any delay.