Prius Rolls Back When Parked On Incline!

I must be missing something - what's the "e-brake"?

 

<div class='quotetop'>QUOTE(jfh3\";p=\"97594)</div>

It's an electronic braking system that works across the internet (kinda' like "e-mail"). :mrgreen:

sorry, couldn't resist!

 

<div class='quotetop'>QUOTE(Tideland Prius\";p=\"97598)</div>

Thanks. Didn't even think that "e-brake" was Emergency Brake. Thought the little "e" was for electronic, like "e-mail" and had no clue. Duh.

 

has anyone actually broken a "parking pin" on a vehicle before? People always say how fragile it is, but i dont recell ever hearing a story about anyone breaking one...

i dont live in san francisco or anything, so maybe thats why

 

Well, we didn't break one, but we bent the heck out of it. Brand new Caravan in 89-- and we immediately took a trip to San Diego. Just south of Yuma, Arizona, we decided to go into a market in Mexico, and we wound up parking on a rather steep embankment. When we got back to the van, we couldn't get it out of park. I was pretty sick about my brand new car. We finally did manage to rock the car enough for it to release, but we had to get that pin adjusted several times during the life of that car. Incidentally, I gave it to my daughter eight years later with 114,000 miles on it, and she drove it a long time. The only major problems with it were with the A/C.

Beth

 

The Prius has an incline sensor that adjusts the amount of torque provided by the electrical motor when no peddle applied to just less than enough to hold it on a hill. This is designed to mimic the action of an automatic transmission. I believe that this info is in the NCF guide.

 

Always use the parking brake. Then you don't spend any time considering whether to use it, no time discovering whether it's set or not, and have no danger of not setting it when you should have done.

 

I don't think any car manufacturer is going to put something in their cars that isn't necessary ($$$$). Anyway, I hate that feeling when I park on an incline and it rolls downhill a bit before the tranny stops it. I'm sure the parking pawl is strong enough to handle it, but just thinking about a couple thousand pounds of rolling weight resting on a little metal bar. I prefer to use the e-brake.

It definitely is a necessity for standard transmissions. I remember watching the local news not too long ago, a toddler was killed in his driveway when his parent's pickup truck popped out of gear and quietly rolled down the driveway... no e-brake.

 

<div class='quotetop'>QUOTE(DavidY\";p=\"97803)</div>

Way back in high school, a friend of mine almost got himself killed because he didn't use the parking brake.

His Dad helped him restore a 1967 Chevy half ton pickup. It had the typical 350 Chevy V8 and a four speed stick instead of an auto. They spent a lot of time and effort on the motor, it was tuned just right so it always started instantly.

He had it parked in front of the garage and opened the passenger door to climb in. His knee brushed against the ignition switch and he managed to jar it to Start. Of course, the 350 fired instantly, and the truck hummed towards the garage, through the door, and into his Dad's brand-new Chrysler Fifth Avenue before he shut off the motor.

The way he explained it, it happened so fast by the time he switched off the ignition, the truck had already hit the Chrysler.

There wasn't too much damage to the Chrysler. Cars were pretty stout 27 years ago, just a small ding on the rear bumper. The Chevy had been parked in bull-low so it going fairly slow when it hit the garage. The garage door was wrecked, knocked right off the track.

He had to work off the damage for 6 months, and became obsessive about parking brakes. He still is too.

 

The only reason to not use the parking brake 'everytime' you park is that your just to damn lazy. They couldn't make any easier unless it was attached to your butt and activated when you got out of the seat.

Use of the brake One: builds a good habit for when you might really need it and forget to use it because you were'nt in the habit, two, use keeps the mechanism working properly, three, they diddn't go through all that trouble to put in a piece of interesting artwork near the floorboards, four all you have to do is step on it it for christ's sake once for on and a second time for off. I don't even think about it anymore, its like when I get in and out of the car my foot just hits the thing on the way in or out.

 

<div class='quotetop'>QUOTE(KTPhil\";p=\"97044)</div>

Yeah, I hear all the time about how the parking pawl breaks off and cars go careening out of control without a driver. If you have ever had an automatic transmission apart, you would realize how absurd that comment is. The case would probably break before the parking pawl. If it were that "fragile", don't you think the NTSB would be all over Toyota.

Ron

 

The Butt Brake! What a great invention!

 

Ron:

My folks had either a '74 or '75 Ford LTD. My Dad thinks it was either a C5 or C6 auto, he can't remember now. There was a lot of trouble with the pawl "tripping" and the car rolling away.

It happened at least once that my Dad recalls, though no damage done as the car rolled onto the lawn and stopped. He became picky about parking brakes after that.

Ford's solution? A sticker they mailed to you, that you stuck on the dash "Apply parking brake before leaving car"

I have taken apart THM 350 and THM 400 auto transmissions, also Ford C6 and Chrysler 727. The parking pawl, at least in those transmissions, is very stout indeed.

However, I've always noticed nicks or gouges on the face of the pawl, and also on the splines where it catches. That tells me folks either slammed it into Park while the car was still rolling, or they parked on an incline without using the parking brake.

Jay

 

Ever notice that when you're parked sitting in your car, reading or listening to the radio with the AC on (which gives the reason for being in READY), the car moves a bit when it starts ICE to charge?

Well, that same process could be used to unload the pawl. Unlike other transmissions, the car does not actually go into neutral. It always has a connection to the wheels, though the power delivered determines the load of MG1.

 

<div class='quotetop'>QUOTE(Mystery Squid\";p=\"97124)</div>

How do you PARK in D? My prius came equipped with a nice large button with a P on it and when I come to a stop on an incline I just press P and it will not roll.[/b][/quote]

No, see, I was already parked on an incline with the e-brake on and everything. So, I get into the Prius, put my foot on the brake, push the Power button, got the "Ready" indicator, released the e-brake (while my other foot is on the brake), then "shifted" it into "D". So, just for kicks, I took my foot off the brake, without touching the accelerator, and she started rolling back... [/b][/quote]

I must be missing something here. This is different from any other vehicle how? Any vehicle will roll backwards when in "D" given enough incline. The amount of roll back is a function of gear ratio, engine rpm, frictional losses, and torque converter multiplication factor. Once you have shifted into "D", gravity will take effect unless countered by enough powertrain torque. Again, this happens with any automatic.

 

<div class='quotetop'>QUOTE(DanMan32\";p=\"98310)</div>

The engine is transverse mounted. So any torque related to starting/stopping will be a fore/aft motion.

In a conventional front engine RWD car/pickup, the torque is translated left or right. As an example back when I used to powerbrake my 1984 Ford F-150 (Stock it was too gutless to do that) the entire truck would hunker left and the right wheel would light up.

 

<div class='quotetop'>QUOTE(DanMan32\";p=\"98310)</div>

I thought the same as you on this one, but the more I thought about it, the less I think that it moves the car, I think what happens is the inertia to start MG1 rotating rocks the whole power unit on it's mounts and that makes the car feel like it's moving. Yes it is but it's reacting to the power unit rocking. From looking at MG1 I'd hazzard a guess that the rotor wieighs in the neighbourhood of 20-25 lbs. A lot of mass to move from 0 rpm to 3600 rpm in a half second or so.

 

I doubt it. Remember, the gears are all engaged, only the parking pawl is preventing the car from moving, and it has some play.
Try pushing the car while in park. You can rock it quite a bit.

So, the ICE/MG1 can move the car as far as the pawl play will allow. I doubt you would feel any motion if the parking brake (or hydraulic brake for that matter) were engaged.