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Summary
  • If your vehicle moves just a little bit after shifting to park, it could be because the parking pawl landed on top of one of the notches on the output shaft and not in between them. When this happens, the output shaft will need to move before that pawl can land in between one of the notches.
  • If your vehicle lurches forward or backward and it moves more than a few inches, then there’s likely an issue with the parking pawl.
  • To prevent excessive wear on the parking pawl, engage your parking brake first before slightly lifting your foot off the brake pedal when parking.

Switching your shift lever to park when you’re parking ensures that your vehicle doesn’t move while parked. However, there could be some instances where your vehicle rolls or lurches after shifting to park. When this happens, there could be issues with your vehicle’s transmission. In this article, we’ll discuss what park setting does and why your car is rolling backward while in park.

What the Park Setting Does

Before we discuss possible reasons why setting the transmission to park fails to hold your vehicle in place, we have to know how it works. When the transmission is set to park, a parking pawl locks onto a notch on the output shaft to lock it into place and keep it from moving. Since the output shaft is connected to your vehicle’s drive wheels, it essentially acts like a brake and keeps your vehicle from moving.

diagram of an engaged parking pawl
Diagram showing basic design of the parking pawl engaged | Image Source: Richard McCuistian

Parking pawl and gear designs vary in many ways, but they all consist of a strong, thick “dog” like the one in the illustration that settles into an equally strong park pawl gear with wide, square teeth, and the gear is thick. 

The park pawl gear is affixed to the output shaft. The park pawl lever/dog pivots on a steel pin affixed to a very strong boss cast into the transmission case.

The park pawl is spring loaded so that when the transmission is not park, the pawl automatically raises its dog out of the way to allow the park pawl gear to allow the output shaft to spin freely so the vehicle can move.

The park pawl is spring loaded so that when the transmission is not park, the pawl automatically raises its “dog” out of the way to allow the park pawl gear to allow the output shaft to spin freely so the vehicle can move.

Richard McCuistian, ASE Certified Master Automobile Technician

What Causes A Car to Roll In Park?

There are two main reasons why a car rolls while in park when it is on an incline when there’s nothing wrong with the transmission.

Parking Pawl Settling Into Gears

As previously mentioned, a parking pawl acts as a brake of some sort when it locks onto the output shaft. However, the pawl can sometimes land on top of one of the notches on the output shaft and not in between them. When this happens, the output shaft will need to move before that pawl can land in between one of the notches. If your vehicle moves slightly even after you moved it into park, it could just be because the output shaft gear is settling onto the parking pawl. After this initial movement, the parking pawl should stop your vehicle from moving.

Worn-Out Universal Joint

Another possible reason for a small amount of movement is a worn-out universal joint, which is found on each end of the driveshafts of rear-wheel drive vehicles.

, Possible Reasons Why Your Car Rolls In Park

Pro Tips are nuggets of information direct from ASE-certified automobile technicians working with CarParts.com, which may include unique, personal insights based on their years of experience working in the automotive industry. These can help you make more informed decisions about your car.

Pro Tip: Usually, though, a u-joint won’t have enough slack to notice the vehicle moving when it’s in park. It will have made a lot of squeaking noises long before being worn to the point that the needles are gone, so this isn’t usually even a factor. A person who ignored the vibrations, clicking and clacking, and all the other things a u-joint does as it wears completely out won’t even notice a slight bit of movement after the vehicle is placed in park.

Damaged Parking Pawl

If your vehicle lurches forward or backward and it moves more than a few inches, then there’s likely an issue. A possible cause could be a damaged or worn-out parking pawl, which can cause it to slip or not engage properly. This can be extremely dangerous since your vehicle can roll downhill and damage property or harm people. This is why it’s important to always engage your vehicle’s parking brake, especially when you’re parking on an incline.

, Possible Reasons Why Your Car Rolls In Park

Pro Tips are nuggets of information direct from ASE-certified automobile technicians working with CarParts.com, which may include unique, personal insights based on their years of experience working in the automotive industry. These can help you make more informed decisions about your car.

Pro Tip: Usually the park pawl can handle just about anything. But if somebody has put the transmission in park a lot while the vehicle is moving, it can damage the park pawl or its pin and mounting boss.

If you’ve observed that your vehicle has this issue, you should have a mechanic check it immediately. Ignoring this issue can further damage your transmission and make repairs more expensive.

Misadjusted Shift Linkage

sample image of a shift cable and linkage
If the shift cable and/or the shift linkage is out of adjustment (see photo), you may put the gear selector in park but the transmission may not fully engage the park pawl. If you ever catch your vehicle doing this, lock the park brake every time you park until you can get the damaged or misadjusted linkage corrected. People get fatally injured by vehicles that roll away because of this, so don’t take it lightly if your vehicle develops this problem. Some newer vehicles have electronic park systems and this is an entirely different world when it comes to putting the vehicle in park. | Image Source: Richard McCuistian

How to Prevent Excessive Wear on Parking Pawl

When parked, you shouldn’t solely rely on the transmission being in park to keep the vehicle from moving because it puts a lot of stress on the pawl and drivetrain components. This is why you should engage your vehicle’s parking brake or hand brake before shifting your vehicle to park.

If the shift lever is switched to park and the vehicle’s brakes are released when the parking brake isn’t pulled yet, then the vehicle’s weight will rest on the parking pawl rather than the brakes. When the parking pawl is used like this, it’ll wear and weaken, which can lead to premature failure.

How to Properly Park on an Incline

Once you’ve driven to your intended parking spot, engage your parking or parking brake first before slightly lifting your foot off the brake pedal. This transfers some of the vehicle’s weight to the parking brake. Your vehicle’s parking pawl won’t bear load as long as you engage your vehicle’s parking brake first before releasing the brake pedal. This method ensures that most of the vehicle’s weight is on the parking brake, not the parking pawl.

About The Authors
Written By Automotive and Tech Writers

The CarParts.com Research Team is composed of experienced automotive and tech writers working with (ASE)-certified automobile technicians and automotive journalists to bring up-to-date, helpful information to car owners in the US. Guided by CarParts.com's thorough editorial process, our team strives to produce guides and resources DIYers and casual car owners can trust.

Reviewed By Technical Reviewer at CarParts.com

Richard McCuistian has worked for nearly 50 years in the automotive field as a professional technician, an instructor, and a freelance automotive writer for Motor Age, ACtion magazine, Power Stroke Registry, and others. Richard is ASE certified for more than 30 years in 10 categories, including L1 Advanced Engine Performance and Light Vehicle Diesel.

Any information provided on this Website is for informational purposes only and is not intended to replace consultation with a professional mechanic. The accuracy and timeliness of the information may change from the time of publication.

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