If Your Car Rolls in Park it Could Mean Your Transmission is About to Fail
If you have an automatic transmission, you expect your car to stay in place when you put it in park. If your car rolls when in park, or your transmission is slipping or you’re experiencing other issues, bring your car to AAMCO for a complete Vehicle Courtesy Check. This will help identify any issues that need to be looked into and possibly repaired. See our current specials and coupons.
Automatic transmissions are the most complex mechanical systems in a car. There are over 800 moving parts in a transmission, so when something goes wrong it’s a good idea to have it checked out – especially something like your car rolling when it’s supposed to be parked. This can be a safety hazard and result in damage and injury – or even worse, as proven by the tragic story of the actor, Anton Yelchin. In that case, the design of the shifter was a major safety issue, and cars with that feature are now under recall. But whether due to design or mechanical failure, if your car rolls when it is in park, you should to take it to a mechanic right away.
When we put our cars in park, we expect them to stay where they are. But there are certain parts of the transmission that are key to keeping the car from rolling, especially if the car is on an incline. We’ll call these parts the parking mechanism, and these parts make it possible to:
- Disengage the parking mechanism when the car is on an incline
- Engage the parking mechanism even when the lever doesn’t line up with the gear
- Prevent the lever from disengaging and permitting the car to roll
When the transmission is shifted into park, a lever called the parking pawl engages the teeth on the transmission output – the piece of the transmission that connects to the driveshaft. If this piece or the transmission can’t spin, the car can’t move.
The parking mechanism is able to disengage from the transmission because it is tapered on both sides, which also helps the parking brake disengage when parked on a hill. When a car is parked on an incline, a lot of stress is placed on the parking mechanism, which means it is more difficult for the mechanism to engage and disengage – be put into and out of park.
A Little Roll is OK
If the parking mechanism lines up so it goes into one of the notches between the teeth on the output gear section, the tapered bushing will push the mechanism down. If the mechanism lines up on one of the high spots on the output, the spring pushes on the tapered bushing and the lever will not lock into place until the car rolls a little so the teeth can line up with the pawl. This is why your car rolls a little bit after you put it in park and let off the brake. It has to roll a little for the teeth on the output to line up so the parking mechanism can click into place and stop the transmission from spinning.
Your car’s transmission will wear over the years. Believe it or not, even just parking can wear on the transmission. The parking mechanism can experience greater than normal wear if you consistently park on inclines. One thing to remember if you do have to park on inclines a lot – and it’s just good parking practice – is to set the parking brake before you put the car in park. This way any pressure from an incline will be absorbed by the brake and it won’t be up to the parking mechanism all by itself to hold all that weight and keep your car in place.
A Lot of Roll is Dangerous
If your car rolls significantly – more than an inch or two – when first put in park, bring it to your local Colorado AAMCO as soon as you can for inspection. This is a dangerous condition that could cause injury to people, damage to property, or worse if not addressed quickly by a transmission expert. Whether your car rolls forwards or backwards, it is an indicator of either the parking mechanism being worn out, or something else such as the engagement of the pawl just not working. If you think there is an issue with your transmission, you should have it checked immediately.