The transmission system, as you may probably know, is a crucial component of an automatic car. After all, it’s what enables the car to slow down or accelerate as needed by adjusting the gear ratio between the engine and the drive wheels.
If there’s a problem with your transmission system, be sure to experience unexpected transmission jerks.
What causes these automatic transmission jerks when slowing down?
The short answer is; a few things, including gears that don’t properly fit together, worn-out transmission bands, and contaminated or low levels of transmission fluid.
Causes and the Possible Solutions Of A Jerky Automatic Transmission When Slowing Down
1. When Gears Don’t Properly Fit Together
The automatic transmission comes with four different gears that fit together into a single system; D(Drive), N(Neutral), P(Park), and R(Reverse).
Each gear performs the same function as the name implies. For example, the Drive Gear gets the car in motion, the Neutral Gear puts the car out of motion, the Reverse Gear allows for a reverse motion, and the Park Gear performs the same function as the emergency parking brake/handbrake in a manual car.
With time, automatic transmission gears will sustain wear and tear, and significant wear and tear will cause them to stop fitting together properly as they should.
This can lead to transmission jerks when slowing down and other problems. These include lots of grinding and clunking for the engine, a jerky shifting experience, and harsh gear engagement.
Apart from that, the car may have trouble engaging a gear and keep on slipping out of gear.
Solution: Replacing your worn-out gear(s) may help fix the automatic transmission jerks when slowing down if the gear(s) are to blame for that.
2. Worn Out Transmission Bands
Transmission bands are the steel rings that run around some sections of the gear train and connect to its housing. Linked to the gears in an automatic transmission, TBs hold a clutch drum during shifting. The transmission typically has two transmission bands and four clutches.
Just like gears, they will wear out over time and stop fitting together properly. Besides normal wear and tear, they may also degrade due to inadequate transmission fluid and being overtightened around the gear train.
This can cause a myriad of problems including a jerk motion when decelerating or slowing down as the bands encounter trouble engaging and releasing the clutch drum in a certain order.
The rest include weak, slow, or delayed acceleration, engine chugs or revs, and strange noises like whining or grinding. You may also experience hard shifting or trouble shifting gears, notice strange smells like that of something burning, or be unable to engage the reverse gear,
Solution: Replacing your damaged transmission band(s) may help fix the automatic transmission jerks when slowing down if it’s being caused by the band(s).
3. Contaminated Transmission Fluid
As you may already know, the work of transmission fluid in an automatic or manual car is to generate the hydraulic pressure necessary to engage gears.
Over time, the metallic parts in your transmission system may wear away/“erode” into the fluid, making it very unhealthy for your transmission system in general.
Eventually, it will be unable to perform its duty as expected, paving the way for many issues including experiencing jerky motions when the car is slowing down.
How do you know that contaminated transmission fluid is the reason behind your automatic transmission jerks when slowing down?
It’s simple, look at the color of your fluid, using the transmission dipstick that is normally on the driver’s side or the passenger side of the engine bay, depending on the car–i.e. front-wheel-drive car or rear-wheel-drive one.
Is it reddish-pink as a healthy transmission fluid should be? If it’s any other color apart from that e.g brown, black, or gray, that’s a sign that you have a dirty and contaminated fluid.
Solution: Replace your transmission fluid.
4. Low Transmission Fluid Levels
Low transmission fluid levels can also cause your car to slow down in a jerky manner. Remember that the work of the fluid is to generate hydraulic pressure to engage the gears.
When the fluid is lower than necessary, it won’t be able to generate the sufficient HP required to engage the gears. That can result in many other problems besides jerky decelerations, including gear slippage and the car reaching high RPMs while moving slowly.
To be sure that a low transmission fluid level is what’s causing the jerky motions when slowing down, use the dipstick to check the fluid level.
The stick is often marked “Full”, “Low”, and “Fill”. Check the fluid level against these markings. If it says “Full” or “Fill”, that tells you that you should top up the fluid.
Solution: Top your transmission fluid.
How Much Does It Cost To Fix a Jerky Automatic Transmission
The answer depends on what’s causing the problem. For example, if it’s improperly fitting gears, replacing the affected gear(s) costs between $1,800 to $3,400, plus labor; $500 to $1200, which comes to about $2300 and $4600 in total.
As for worn-out transmission bands, it doesn’t cost much to replace those as there are replacement bands available for as little as under $50 on Amazon.
When it comes to low or contaminated transmission fluid as being the cause of your car’s jerky automatic transmission, replacement automatic transmission fluid typically costs 8-$20 per quart, and many automatic cars require between 5-15 quarts, that’s $40-$300 minus labor. The cost of labor should be between $80 and $110.
If you notice that your automatic car is jerking when decelerating, that could be a sign of many things. For instance, it may signify your gears are worn out and thus not fitting together properly or your transmission bands are worn out and not engaging and releasing the clutch drum accordingly.
If not, it may be an indication that your transmission fluid is contaminated or it’s low and thus not generating enough hydraulic pressure needed for the entire system to work properly. Trust me, ignoring this issue can lead to bigger problems quicker than you may anticipate.