Vehicle parked outside starts moving

A few days ago I parked my truck in my driveway which slopes upward. After about 10 minutes or so the wife asks why I went back out to the truck because the motion camera picked it up moving. When I went back after this incident the truck was indeed in park. Something strange is the wheels appeared to turn into the snow, which would indicate that it didn't stay in park. Any thoughts? Besides the peanut gallery and ghosts....
https://ring.com/share/6782074220238729111

 

WOW.... sure glad it stopped and didnt roll into the street

 

The front wheels are free to move unless in 4WD. Transmission and parking brakes only apply to rear wheels. Guessing back wheels slipped on ice for a bit.

 

That is very strange, and potentially hazardous. Take your ring video and the truck in. Is it possible that you didn’t fully get the selector into the PARK detent?

 

My understanding is your front wheels are free (neutral) while in park unless you are in 4WD. Only your rear wheels are locked while in park in 2WD. My guess is the top layer of ice you parked on began to melt and you lost traction??

 

Beat me to it.

 

That makes sense. I hadn’t even considered the front wheels might be free.

 

What trooper said.

 

Another reason to use 4x4 at the boat ramp even if you don't need it!

 

first good freeze of the year and I totally forgot about physics. Stop at the mailbox, put it in park, open the door to get out just as the truck starts to go backwards.....FAST! pull leg back in, slam the door closed as I take it out of park so I can dodge the tree behind me. I put it in 4WD to park at the mailbox now.

 

crazy ! could have ended a lot worst.

 

In 2wd and in park, only one rear wheel needs to slip for it to move like that. Apply the parking brake, it becomes both rear wheels. Park it in 4wd with the parking brake applied, 3 must slip to move.

But if it’s wet, sloppy or slushy the parking brake has a chance of freezing on if the temps drop when parked. Parking in 4wd without the parking brake might be a better option in that case.

 

Looks like the transmission Park did not engage when it was initially put in Park. When the truck started rolling backwards, the transmission Park mechanism finally hooked up and stopped the truck abruptly. You can see the truck suddenly stopped and rocked back and forth a bit. You can replicate that but may not be good for transmission. When you park again, you can put the transmission on Park, let go of the brakes, you will feel the truck move a little bit then it will stop moving. Now you know the transmission Park is engaged. Apply Parking Brake.

 

That rocking is when the rear tire(s) grabbed traction when it hit a dry patch of driveway.

 

I want to agree with you but I cannot dismiss @art64 's theory completely. If park not engaged would think OP would have noticed when getting out. Just my .02

 

Looks like you have an issue and I’d take that in. Separately I got in the habit of always using the parking brake in park, even on flat surfaces.

 

I do this every time I am on any incline/decline. I hate hearing the parking pawl slam coming out of park! Wife releases the parking brake before taking it out of park half the time and always looks for my rage when it slams.

 

I agree I’d take it to Toyota to see if there is something else. But definitely use the parking brake. If it was on ice it wouldn’t have helped but there might be another issue. That could’ve been a lot worse if someone was behind it.

 

You don't have to lose traction on both rear wheels for the truck to slide. In 2WD, one rear wheel can slide allowing the other wheel to turn backwards relative to the direction the truck is facing. As the truck slides, the wheel that's turning backwards will turn the sliding wheel forward. This will continue until both wheels get traction. If you want to test this, put the truck in park and jack up one rear wheel with a wheeled jack that it can't roll off of. You can fairly easily push the truck around. As you push, the wheels will turn in opposite directions. As others have said, use the parking brake and/or 4WD.

 

Agreed! 100%. I cringe when I am in someone else’s vehicle and they slam it into park and let off the foot brake without first engaging the parking brake.

 

I have nearly 50 years of driving under my belt and I can probably use my fingers to count the number of times I've used the parking brake. If "Park" doesn't mean it, why is it there?

 

My dad and one uncles who is a mechanic says the same thing you say. My other uncle and buddy who has been a mechanic his whole life agrees with me. It’s an age old debate I guess.

 

Agreed. When Park Brake is used like that,why bother? Letting the vehicle's weight rest on the Transmission Park-Pawl before applying the park brake defeats much of the park brake's purpose. I see/hear the same thing happening at boat launches!

 

I was under the impression that if you do that, the entire weight of the vehicle is being held by the pin that holds the transmission, rather than the brakes. Thus, if it wants to roll, that pin will likely break and you'll be out the cost of a new transmission. I always set the brake, shift into neutral to let the parking brake grab then shift into park.

 

This thinking begs the question why something called a "parking" brake exists.

 

It's probably a leftover from the days when automatic transmissions didn't have a Park position, and from the days of manual transmissions when engine compression was low and the weight of the car could turn the engine allowing the car to move.

 

Were your tires hot when you parked the truck?
Heat caused melting snow, re-freezing as ice under the tires, then weigh & gravity take over.

Parking brakes & Seat belts, use them.

 

The only thing I've used my warranty for is having the parking brake adjusted tighter. From the factory it would not hold the weight of the truck in neutral on very minimal slopes.

 

parking brake never works eh..........

 

Damn manual covers everything. This is in the winter driving tips section. The normal parking instructions say to apply parking brake before shifting to park.