Bad News for Lynnay: Her Mother Is Right

Dear Car Talk

Dear Car Talk | Sep 12, 2012

Dear Tom and Ray:

On a recent visit to my home, my "wonderful" mother expanded her range of "helpful" advice-giving to the manner in which I park my car on my steeply sloped driveway. She was deeply concerned about the order in which I engage park and the emergency brake. She advised me that by placing the car in park first and then engaging the emergency brake, I am sure to ruin the transmission. Her motherly recommendation is, of course, to reverse the order, thereby saving the world. I've been unable to find either a confirmation or a denial regarding the proper order for my parking procedures. Would the brothers be willing to provide a final word on this matter? Thanks.

-- Lynnay

TOM: Lynnay, we're going to use the worst four words an adult daughter can hear: Your mother is right.

RAY: Well, her instructions are right. She's wrong about the severity of the consequences, but she is correct that the preferred parking method on a hill is to deploy the parking brake first, to hold the car in place, and then put the transmission in park, to back up the parking brake.

TOM: Here's why. Park works by using a ratcheting mechanism called the parking pawl to lock the output shaft of the transmission. Because of the way the differential works, locking the output shaft allows the driven wheels to turn only if they move in opposite directions. So unless the car is being dragged or it slides (which ain't easy if you're a car), once it's in park, it's not going anywhere.

RAY: But because of the way that ratchet system is designed, if you put the car in park and then it rolls up or down a hill a few feet, the weight of the car ends up resting on the parking pawl, pushing it in tighter than it needs to go.

TOM: Will that ruin your transmission? No. But it can make it hard for you to get the car OUT of park when you go to drive away. Maybe you've even noticed this.

RAY: This is especially true of older cars, where these parts have started to wear out and create "slop," or in cars that have been parked incorrectly on hills for many years -- like yours! Of course, it matters only on steeper hills.

TOM: By applying the parking brake first, you allow the brakes to do the job of holding the wheels in place, so the car doesn't roll and push the park mechanism to the point where it's difficult to remove.

RAY: Then, when you drive away, you do the opposite: You take the car out of park first, and then release the parking brake.

TOM: I know this is a tough blow to absorb, Lynnay. But just remember, this could be a completely isolated case of Mom being right, and have no bearing on whether she also was right about your first three husbands.

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