There are a number of things that can suddenly happen when you’re driving that will be of immediate concern to you, and might even take you a little off-guard. Many of those things are to do with sounds, vibrations and other unexpected happenings that occur when you put on the brakes. We get so used to our car slowing smoothly and quietly, that even the slightest problem felt or heard when we’re braking immediately starts to worry us.

Now imagine that you’ve put on the brakes but your car starts jerking as you slow down. That can be a very harrowing experience, and you’ll doubtless wonder what the heck is going on down there.

Hopefully today’s blog will shed some light on this and give you some clarity so you don’t have to be so afraid of this in the future.

Why Does My Car Jerk When I’m Slowing Down?

Bad Transmission and/or Transmission Leak

When you are slowing down in your car, the transmission will start downshifting to compensate. If the transmission is also faulty, then the shifts won’t be smooth and it might start to generate these jerking motions as the gears bumble downward to where they need to get to.

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

Transmission leaks could be caused by ruptured seals or damage to the undercarriage on your car. 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.

Overly Worn Clutch

A clutch can last on a car for up to 150,000 miles depending on the quality and how it’s used. If your clutch has been on there unchanged for many tens of thousands of miles, it could just be getting to the time where you need a new one. A good way to know if the clutch is to blame is to see if you’re getting these jerking motions as you’re driving at lower speeds (and so in lower gear ratios) and if they go away when in slowing at higher gear ratios.

Damaged Throttle Body

The throttle body controls the air intake supply system. If and when it gets damaged, you’ll end up with an air flow system that can’t control the fuel/air mix and supply properly. It usually manifests the jerking movements when you are idling, if the throttle body is the main problem, and when trying to drive off at low speeds.

Damaged MAF Meter

Your mass airflow (MAF) meter measures air going into the engine. A damaged MAF meter can’t make those readings correctly and so will create a poor balance of air, either not enough or too much, which causes the car to have serious problems, especially at low speeds.

Other Possibilities

Besides the above common factors, other possible causes of that jerking when you slow down could be that:

• Your coil packs need changing
• The engine mounts are worn and thus not holding the engine stably enough
• The turbo is damaged (rare, but possible)

What Should I Do When My Car Jerks When Slowing Down?

The most important thing to remember to do is take your car to an auto shop and have it serviced. There are multiple components that could be going wrong, including all the ones we’ve mentioned above, but possibly even something else. The following are the most likely major servicing jobs you’ll need to have done.

Reflect on Your Gear Shifting (Manual Cars Only)

If you are driving a stick shift, you are in a small minority of drivers in the US — and even a dwindling majority of drivers in Europe — and you may be experiencing jerking motions because your shifting is uneven or poorly timed. Experienced manual car drivers will unlikely not experience jerking for this reason, but if you’ve found yourself driving a stick after a long time of not doing so, this could be one of the reasons.

You can save yourself some expensive auto shop bills by just having another experienced driver see your shifting and seeing if it’s wrong. You can also check yourself, are these jerking motions happening as your downshifting in particular?

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

Have the Brakes Inspected

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

You might also need new brake pads — do you also hear squealing as you’re slowing down? — but in the more serious cases you might have warped brake rotors where the rotor’s perfectly even surface has been damaged by overly worn brake pads.

Have the Transmission Serviced

If the problem is a faulty transmission, then it’s equally critical that you get that restored to health as quickly 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 your transmission fluid levels are too low, in which case replenishing it is a fast and inexpensive way to solve that issue.

Have the ABS Inspected

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

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

Most Importantly – Don’t Panic

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

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