My car shudders when slowing down – why?

There are a number of things that can suddenly happen when you are driving that will be of immediate concern to you and may even catch you a little off guard. A lot of these things have to do with sounds, vibrations, and other unexpected happenings that occur when you step on the brakes. We have become so used to the smooth, silent deceleration of our car that even the slightest problem felt or heard when braking immediately begins to worry us.

Now imagine that you hit the brakes, but your car starts to jerk when you slow down. This can be a very harrowing experience, and you’ll no doubt wonder what the heck is going on down there.

I hope today’s blog sheds some light on this and gives you some clarity so you don’t have to be so scared about it in the future.

Why does my car shake when I’m slowing down?

Bad Transmission and/or Transmission Leakage

When you are slowing down in your car, the transmission will start to downshift to compensate. If the transmission is also faulty, the shifts won’t be smooth and can start to generate these jerky movements as the gears slow down to where they need to go.

Likewise, it could be a faulty torque converter, which is the component that regulates the rate at which the engine and transmission work together. If the jerk is happening in particular when you hit low speeds, the torque converter is the most likely candidate.

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transmission leaks it could be caused by broken seals or damage to your car’s chassis. You can inspect the underside of your vehicle to see if you can see any signs of pink/red transmission fluid dripping or pooling on the floor.

excessively worn clutch

A clutch can last up to 150,000 miles on a car depending on the quality and how it is used. If your clutch has been unchanged for many tens of thousands of miles, the time may be coming when you need a new one. A good way to tell if the clutch is at fault is to see if you are getting these jerky movements when driving at lower speeds (and so in lower gear ratios) and whether they disappear when decelerating in higher gear ratios.

Damaged throttle body

The throttle body controls the air intake feed system. If and when it gets damaged, you will end up with an airflow system that cannot control the fuel/air mixture and deliver properly. It usually manifests the jerks when you are idling, if the throttle body is the main problem and when trying to pull away at low speeds.

Damaged MAF meter

Its mass airflow (MAF) measures the air entering the engine. A damaged MAF gauge is unable to take these readings correctly and therefore creates an under, under or over air balance which causes serious problems for the car, particularly at low speeds.

Other Possibilities

In addition to the above common factors, other possible causes of this jerk when you slow down could be:

  • Your coil packs need to be replaced.
  • Engine mounts are worn and therefore do not hold the engine stably enough
  • The turbo is damaged (rare but possible)
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What should I do when my car jerks when decelerating?

The most important thing to remember to do is to take your car to a mechanic and have it serviced. There are a number of components that could be going wrong, including all the ones we mentioned above, but possibly even something else. The following are the most likely major maintenance jobs you will need to perform.

Consider shifting gears (manual cars only)

If you’re driving a stick shift, you’re one of a small minority of drivers in the US – and even a dwindling majority of drivers in Europe – and may be experiencing jerky shifts because your shift is erratic or poorly timed. Experienced manual car drivers probably won’t experience jerks for this reason, but if you’ve found yourself driving with a stick after a long time without doing so, this could be one of the reasons.

You can save yourself some expensive mechanic shop bills just by having another experienced driver look at your change and see if it’s wrong. You can also check yourself, are these sudden movements happening like your particular downshift?

At least rule these factors out first if you drive a manual car.

erratic car transmission

Have the brakes inspected

With the obvious already ruled out, it’s time to resort to other likely explanations, the first of which is that your brakes need an inspection and/or maintenance. Minor issues that can cause this issue include air in the brake lines which can be bled quite easily.

You may also need new brake pads – do you also hear squeaks as you slow down? – but in the most serious cases, you can have warped brake rotors, where the perfectly even surface of the rotor has been damaged by excessively worn brake pads.

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Maintain the transmission

If the problem is a faulty transmission, it is equally important that you get it back to health as soon as possible. Transmission repairs, like replacing a torque converter, can be an expensive task because the transmission is one of the most intricate and complex systems in your vehicle. However, these are also repairs that your car cannot do without.

Hopefully an inspection will reveal something simple like the transmission fluid levels are too low; in that case, refueling it is a quick and inexpensive way to resolve this issue.

Have the ABS inspected

The anti-lock brake system (ABS) is also a key component in slowing down your car and therefore could also be the culprit. Have you noticed the ABS warning light appearing on the dashboard display?

This could indicate that the ABS has a faulty sensor, bad wiring, debris buildup, or some other issue that is affecting its normal operation.

Most importantly – don’t panic

It’s critical to remember that no matter how bad the sudden movement is or the noises he’s making, don’t panic. Keep calm and carefully drive the car at a slow, steady pace to the safety of a parking lot, at least, or to an auto repair shop if you can. If what is happening is clearly affecting the safe operation of the car, you should pull over to a safe location and call roadside assistance to tow the vehicle for you. No amount of brake or other damage to the car is worth risking your life.

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