Car continues to roll back after putting it in park

[lisamaza]

I'm having a problem with the parking on my car. This started happening recently. I'm not on an incline, but when i put the car in park, it continues to roll back anywhere from 6 to 12 inches. Sometimes it happens. Sometimes it doesn't.

Last night I had to use the emergency brake to stop it from rolling. Is this expensive to fix? I know nothing about cars and have an appt with the toyota dealership on monday and want to know how expensive it will be, or whether it requires fixing at all.

Thanks to anyone who can help.

This thread is over 3 years old. Just because a noob necro-ed it doesn't mean we all need to reply again.

Zenmervolt - AnandTech Moderator

 

[punjabiplaya]

is it an auto? selector cable might be loose

 

[HeXen]

sounds like the parking gear may be missing some teeth. a bar slides into these teeth of a gear attached to the shaft inside transmission. Likely your missing 1 or 2 and is why it only hapens every so often. so i bet if you put it back into drive and move up a foot or so and put it back in park, it'll be normal.

next time, try rocking the car back and forth, make sure it wont go past the 6-12 inches. I would probably just get used to using the parking brake, but i'd guess it would be a couple hundred bucks to fix?

 

[Demo24]

Parking brake is there for this reason. Technically Park isn't designed to be the sole stopping force, but I guess these days they build them strong enough to make it work well enough.

 

[Harvey]

As System_Mechanic suggests, your parking gear may be missing some teeth or otherwise failing.

That's why you should always use your parking brake, as well, instead of just relying on park gear, alone. Park gear is intended to be a means of locking the drive shaft, and it can fail, especially on an incline.

 

[lisamaza]

thanks for responding. Do you think this is a problem that needs to get fixed? Is it safe to leave it as is?

 

[Throckmorton]

The parking pawl is probably damaged. That's why you should put it in neutral, pull the hand brake, then put it in P. It sounds like you don't use the parking brake at all, so it's no wonder.

If the pawl does grab at some point I guess it can still function as a backup to the park brake, but I'm not sure.

 

[LTC8K6]

thanks for responding. Do you think this is a problem that needs to get fixed? Is it safe to leave it as is?

Yes it needs to get fixed because it is probably going to fail completely soon. Soon it will roll back and break the last bits.

Then only the parking brake will be holding the car in place, and apparently you don't know what that is for...

 

[ShawnD1]

Parking brake is there for this reason. Technically Park isn't designed to be the sole stopping force, but I guess these days they build them strong enough to make it work well enough.

Wait, you guys are just talking about the park gear on an automatic transmission? You're not supposed to rely on that gear. It doesn't actually lock the wheels. What the parking gear does is lock the output from the transmission.

The output of the transmission connects to the differential. The differential has a total of 3 connections on it: left wheel, right wheel, transmission. Most cars have open differentials which means the left and right wheels have nothing to really tie them together and match their speed. While the output of the transmission is locked, the left and right wheels are still capable of spinning. You can see this effect if you have a Niko brand radio control car. While holding the car in the air, you'll notice that spinning the right tire in the forward direction causes the left tire to spin in the reverse direction. Your car's differential is exactly the same as this. If one tire is capable of slipping (ice) and the other has full traction, the tire with traction will try to rotate down the hill and the tire on ice will try to rotate up the hill.

This is why you NEVER use only the parking gear. It doesn't lock the wheels!


edit. It's always fun reading people complain about this issue. This kind of thing is why you should buy your son a remote controlled car. He'll learn a lot from it
http://www.dodgetalk.com/forums/showthread.php?t=321008

I had something weird happen tonight when I got home and parked on my icy driveway which has a very slight uphill incline. I put the truck in park and the truck started ti creep backward. I thought it might be the ice, but the right rear tire was rolling backwards (truck was going backwards) but the left rear tire was rolling forward on the ice while the truck was sliding backwards.

I was able to back up, drive back in, and repeat this multiple times. If I put on the parking brake then the truck would stay still, but without the parking brake the wheels would roll in opposite directions in Park.

Very strange...

 

[HeXen]

i know people who wont use the Pbrake with a Manual. they just put in gear and expect it to be there when they get back. lol

 

[LTC8K6]

Wait, you guys are just talking about the park gear on an automatic transmission? You're not supposed to rely on that gear. It doesn't actually lock the wheels. What the parking gear does is lock the output from the transmission.

The output of the transmission connects to the differential. The differential has a total of 3 connections on it: left wheel, right wheel, transmission. Most cars have open differentials which means the left and right wheels have nothing to really tie them together and match their speed. While the output of the transmission is locked, the left and right wheels are still capable of spinning. You can see this effect if you have a Niko brand radio control car. While holding the car in the air, you'll notice that spinning the right tire in the forward direction causes the left tire to spin in the reverse direction. Your car's differential is exactly the same as this. If one tire is capable of slipping (ice) and the other has full traction, the tire with traction will try to rotate down the hill and the tire on ice will try to rotate up the hill.

This is why you NEVER use only the parking gear. It doesn't lock the wheels!

Are you sure you're allowed to drive?

 

[ShawnD1]

Are you sure you're allowed to drive?

Keep on trollin. Don't let reality stop you :wub:


What's interesting is that anandtech is one of the top results if you try googling for more information about the parking gear.
http://forums.anandtech.com/showthread.php?t=2086175&page=2

(which wheels are affected by "park") doesn't even matter with an open diff anyway; the axles and spider gears are free to pivot even with the output shaft all the way through the carrier locked by the pawl. They can't turn together in uniform direction in park, as the carrier will bind, but lift one drive wheel off the ground so that's it's free to reverse, and the other wheel will easily roll in park.

I'd wager that 3000+ lbs on a single drive wheel on an incline would be enough to overcome the clutches in a LSD and still roll also. Wheel chocks are your best bet if you're paranoid and feel you need to jack one side of the car 10 feet into the air for half an hour to change a tire.

Many other people, including the person who wrote wikipedia, say the exact same thing. It's almost like physics predicts things and they're assumed to be true because the same result happens every time it is tested.

 

[LTC8K6]

Keep on trollin. Don't let reality stop you :wub:


What's interesting is that anandtech is one of the top results if you try googling for more information about the parking gear.
http://forums.anandtech.com/showthread.php?t=2086175&page=2



Many other people, including the person who wrote wikipedia, say the exact same thing. It's almost like physics predicts things and they're assumed to be true because the same result happens every time it is tested.

Well, most cars these days are FWD with the parking brake on a rear wheel...

 

[HeXen]

in reality, very few people with auto transmissions use the Pbrake when parked on a flat surface. Most people don't even turn their tires towards the curb either when they park or even park facing the right way much less use a turn signal...so its not to judge the OP that he didn't use the Pbrake before this started occurring but does need to now.

 

[Throckmorton]

Are you sure you're allowed to drive?

He's right. That can happen if you rely on the parking pawl instead of using the brake.

I think the source of the problem is people calling it an "emergency brake". It's not an emergency brake, it can't stop the car in an emergency. It's for parking.

 

[LTC8K6]

He's right. That can happen if you rely on the parking pawl instead of using the brake.

I think the source of the problem is people calling it an "emergency brake". It's not an emergency brake, it can't stop the car in an emergency. It's for parking.

Not really, he left out most of the vehicles in the USA.

 

[Apex]

i know people who wont use the Pbrake with a Manual. they just put in gear and expect it to be there when they get back. lol

I do that at the track.

 

[Throckmorton]

Not really, he left out most of the vehicles in the USA.

No he didn't. A FWD car has a differential too.

 

[LTC8K6]

No he didn't. A FWD car has a differential too.

So what? I have full time four wheel drive.

And I always use my pbrake.

 

[Howard]

in reality, very few people with auto transmissions use the Pbrake when parked on a flat surface.

Is this a statistic of some sort?

 

[coxmaster]

Is this a statistic of some sort?

Well, everybody that rides with me (ever) asks why I use the parking brake even though it is an automatic.

In general most people with an automatic simply don't use the parking brake (i do use it)

 

[Howard]

Well, everybody that rides with me (ever) asks why I use the parking brake even though it is an automatic.

In general most people with an automatic simply don't use the parking brake (i do use it)

Lame. I wonder what they think the parking brake is for, then. God forbid they use it only to initiate oversteer.

 

[Harvey]

in reality, very few people with auto transmissions use the Pbrake when parked on a flat surface. Most people don't even turn their tires towards the curb either when they park or even park facing the right way much less use a turn signal...so its not to judge the OP that he didn't use the Pbrake before this started occurring but does need to now.

So many volunteers for Darwin awards!

 

[LTC8K6]

I just use a rock that I keep in the trunk...

 

[Zenmervolt]

He's right. That can happen if you rely on the parking pawl instead of using the brake.

"Can" happen and "has even a remote possibility of happening in the real world" are very different things.

While it's definitely possible if one drivewheel is on glare ice and the other has grip and the incline is steep, the chances of those factors coming together are incredibly slim. Better than 99% of the time (hell, probably better than 99.9999% of the time) just putting the automatic in "Park" is perfectly fine.

And this is coming from someone who always uses his parking brake.

ZV