There are various reasons why your car is jerking every time it slows down. These include faulty brakes, transmission issues, mounts and bushings, and engine problems.
We will now discuss what might be the case in your situation and how you can remedy it.
9 Causes of Jerking When Slowing Down
Brakes are one of the most common reasons why your car is jerking. Car jerks caused by braking can be due to several reasons.
A warped or damaged brake rotor is caused by wear, heat, or rapid cooling. This causes vibration or a pulsing feeling every time you apply brakes. To know for sure, it’s a warped brake rotor, and there will be a grinding or rumbling noise every time you apply brakes in addition to the car jerks.
Worn brake pads can also be the reason, or sometimes a collection of debris like sand and rust can cause uneven brake pressure on the rotor, causing it to jerk the car every time you brake. To confirm this, check for a squealing or a high-pitched noise every time you apply brakes.
ABS (Anti-lock Breaking System) is responsible for applying maximum brake pressure without locking up your wheels. When slowing down, car jerks could be harmless and might activate your ABS under intense breaking. Checking this is very easy.
Every time ABS kicks in, you will see an ABS light flashing in your dash. If it’s coming on even under light braking or stays on for some time, it could be a faulty ABS sensor or an ABS actuator.
The brake booster works using a vacuum in the chamber. Air brake lines move the brake fluid in the brake reservoir to the calipers. The diaphragm in the brake booster and the air brake lines could leak and may cause car jerks and ineffective braking. To confirm this, press down the brake consecutively or pump it and check if the brake is getting too pressed down or feels spongy.
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A warped brake rotor would require lathe and alignment work, costing around $10-$30, and can only be done by a professional. But it is recommended that you change the rotor because the old repaired rotor will be more prone to warping again. This replacement will set you back around $300-$500 per axle with parts and labor. This may be pricey, but it is safer for you and the cars around.
Bad Engine Mounts
Two car components require proper mounts: the engine and the transmission. Every time you slow down your vehicle, weak or damaged mounts can cause natural vibration of each element to cause car jerks, as whenever a car is slowing down, there is a shift in weight which may induce rocking.
To confirm mount issues, every time the car slows down and you feel car jerks, just let go of the brakes and see if car jerks are still present. If they are, press the gas pedal slightly to check if the car jerks go away when accelerating. During engine braking, the engine and the transmission are under heavy load, and this causes strain on the mounts.
If the mounts are weak or damaged, they won’t be able to control the car jerks caused by engine vibrations under a heavy load.
Replacing the mount is the only option, and it is recommended to have it done by a car shop as it requires proper alignment and equipment. The car’s make and model will set you back $200-$500.
Bushings and Suspension
Your steering rack, axles, shock absorbers, springs, rods, joints, bearings, and wheels are all mounted and kept in place using bushings that use different kinds of rubbers and metals to allow required movement in designated directions, restrict any unnecessary movements and absorb any vibrations.
They are placed in proper alignments and balanced to ensure no disproportions between one side of the car and the opposite side. This provides smooth driving, handling, and maneuvering. To make sure the suspension is responsible for the, do the following to rule out different parts of the suspension.
To check for alignment, get the car up to high (permitted) speeds on a long stretch of road. Center the steering wheel to make sure the vehicle is going straight and let go of the wheel (while keeping your hands in place to catch it again) and observe if the car is swaying in one direction as soon as you let go.
Do this several times to ensure it is the alignment, not wind from a car passing by or the wind direction.
For balancing issues, you will observe the car jerks when slowing down from high speeds only, but you won’t feel a thing slowing down from low speeds.
If the steering rack or axle bushings are faulty, you will feel most of the car jerks and vibration in the steering wheel, not the car frame.
Alignment and balancing will require a trip to the workshop because that is done using a computer and a proper designated set of gadgets. It will cost around $90.
The axle, steering rack, and other bushing replacements will cost between $75-$300 depending on the car’s make and model and how many bushings need to be changed.
Manual car jerks more often than automatic transmission due to the engine breaking being more intense because the gears are manually controlled compared to an automatic car that constantly shifts gears every time there is a high load on the torque converter.
A manual car jerks more often could be a sign of low transmission oil, a choked transmission oil filter, or a worn-out clutch or clutch pack and clutch slipping. A slipping clutch causes constant pulsation or high-frequency rocking when you let off the gas to coast. Instead of the clutch staying engaged under load, it keeps slipping and frequently engages – disengages.
Low transmission fluid creates additional friction between the moving parts of the transmission. Under heavy loads like coasting or engine braking, the friction increases dramatically, causing severe vibrations, which are felt as vehicle jerks. To know if it’s a slipping clutch due to clutch wear, the clutch will press in and come out with a spongy feeling rather than a constant firmness.
You will also hear a grinding noise during a gear change. There will also be vibrations when you take off from a stop.
There is a dipstick to check the transmission oil and its level. The condition of the oil will let you know if a filter is choked up or not. Slipping clutch has a pulsating jerk, and a low transmission oil will have a grinding constant car jerk which will arise a few seconds after you let off the gas.
Once you have diagnosed the issue, have the car professionally inspected because driving for too long will cause failure in one of the parts. Clutch pack change will cost $300-$2000.
Transmission Oil and oil filter replacement will cost $70-$250.
Automatic transmission jerks can be due to a few reasons: problems in the torque converter, low or leaking transmission fluid, and faulty transmission sensors.
The torque converter is filled with transmission fluid with a specific viscosity and pressure acting as a clutch.
An ECP (Electronic Pressure Control) solenoid maintains the transmission fluid pressure in the valve body. The valve body has a maze-like structure that navigates the fluid to build pressure or move around to change gears depending on requirements.
An error in the solenoid or valve body causes the liquid not to have enough or varying pressure and causes a vehicle to jerk. Automatic transmission jerks caused by torque converters feel like a slipping clutch with pulsating jerks.
To know for sure, there will be pulsation a few seconds after you let off the gas, harsh or delayed gear changes, problems staying in one gear, car shakes under load, and check engine lights.
Low or leaking transmission fluid causes pressure loss in the torque converter and gear slippage under load, causing vehicle jerks. Check the transmission fluid dipstick and the fluid pan for signs of leakage.
A professional can only make repairs in this situation. The torque converter repair will cost anywhere between $350-$900. Transmission fluid replacement will cost $80-$250.
The throttle body has a set of sensors and parts that maintain the air-fuel ratio during the combustion while controlling the air and informing the ECU so that it can have the suitable fuel amount ready to be injected.
IACV (Idle Air Control Valve) controls the valve on the throttle body that regulates the air volume flow rate depending on the idling and the requirements of the engine RPM and load. If that becomes faulty, it can cause different volumes of air to come through, causing irregular power at idling RPM under load, causing vehicle jerks.
MAP (Manifold Absolute Pressure) sensor senses the vacuum in the intake manifold and determines its incoming load and air volume flow rate. The fault would have the same result as a malfunctioning IACV.
MAF (Mass AirFlow Sensor) measures the mass of the air coming in to determine the air volume flow rate to have the rational amount of fuel injected for combustion. Fault in the MAF sensor causes rich or lean combustion causing knock and jerks under high load.
TPS (Throttle Position Sensor) positions or opens the intake valve depending on the required air volume flow rate and how much the gas pedal is pressed.
A diagnostic tool can check these sensors’ errors by inserting them into the ECU’s OBD port. It gives out specific error codes for each sensor. Replacement of each sensor costs between $20-$100.
Bad Ignition System
Spark Plugs can have carbon buildup over time and cause sparks to have less intensity which may be most noticeable in situations like engine braking when the engine is overworking.
You can check for it by physically inspecting the spark plug and checking for black-brown discoloration.
The distributor Cap has a set of ignition coil plug wires that carry the charge from the ignition coil pack to the spark plugs. If there are leaks, damage to the insulation, or moisture in the distributor cap causes an arc jump; the electric charge is less intense.
This causes misfire and premature ignition causing knocks and vehicle jerks. You can check this by observing jerky acceleration and deceleration. Have it physically inspected by a car electrician to narrow it.
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Ignition coil pack costs between $75-$400. Ignition coil plug wires cost around $20-$100. Spark plugs may set you back $50-$100 each. Labour can easily be between $20-$100.
The fueling system consists of the fuel pump, fuel injectors, fuel filters, fuel strainer, and vacuum hose. Mechanical faults like dirt, clogging, or leaks result in fuel pressure loss, making the car run lean. This causes jerks when you decelerate or accelerate due to insufficient fuel.
The OBD diagnostic tool will show errors as a loss of fuel pressure.
It is better to have it repaired by a professional because different fuel system parts are challenging to locate and diagnose. Depending on the problem, the repairs cost between $50-$200.
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Turbo increases air pressure and air volume flow rate, so more fuel is burned to create more power. If there is a fault in the boost system or damage to the turbo, it may cause a loss in boost or a leak of vacuum in the intake manifold. An irregular supply of air causes jerky engine braking.
Turbo repairs can be pricey or cheap, depending on what’s damaged. Depending on the problem, repairs cost anywhere between $20-$800.
When slowing down, car jerks can be easily avoided if you ensure maintenance is on time. Sometimes a simple issue like a clogged air filter can cause car shakes.
Air filter vacuuming can even clear up the problem. Very few instances can result in expensive repairs, which can be avoided with proper maintenance. In some situations, car jerks are typical such as engine braking.
Manual car jerks are more common than you think, but when slowing down, excessive jerks should always be investigated. In comparison, automatic transmission jerks are not usual, so anything out of the ordinary is a concern.