braking in reverse

Sure hope 48/50 doesn't want to return the car for this. I don't think that is reasonable at all. Again I would hope all the benefits outweigh this small as I believe non issue. Doesn't matter what vehicle for that matter all have some glitches and bugs and this is no different...

 

Finally! If not answers, at least we have someone with some reasonable questions instead of another poster telling me I don't know how to use the brake pedal. Thank you! To answer some of the questions:

1. IV w/Solar & NAV
2. I do sometimes park by just turning the car off and letting it move to park as part of the shutdown process. I do that a lot though, and cannot correlate it specifically to the one time this problem occurred.
3. I do not always wait 15 seconds either before or after putting the car in gear. In fact, I very rarely do. So again, I cannot correlate that action to the problem.

All very good questions, even though I don't have any useful answers. Lets continue to explore these types of helpful lines of reasoning - it doesn't seem to happen to all owners, but it is certainly not an isolated case.

 

For me:
1. IV w/solar and NAV
2. I always push Park before turning off the car, no exceptions
3. I do usually wait at least a few seconds, though not 15. Today when the grabbing happened I was in quite a hurry, so probably didn't wait at all.

 

Raechelseven,

I agree, there has to be some sort of commonality to the issue. Again there is some steps or processes that may be different. Some of those you listed like not waiting 15 seconds (that was just a mean number I picked as I would think all component go through a quick check process), and using the Park Button each time when stopping at your destination versus using the POWER button only.

I know nobody has provided any solid evidence to date of what this issue is, and speculation is quite the norm. I may suggest to that you should try those 2 steps mentioned, (faithfully) for a period of time, I know it may be difficult since it's procedural and your not used to performing it daily, but if you do this I wonder if you won't exhibit the behavior? Since I have not noticed it yet, I follow that regimen daily and on all trips so maybe it has something to do with pressures, computer routines, something for sure...of course there is a possible software upgrade or something, but try those steps to see if you DON'T experience it. I have a Model V and from looking back in the posts I do see it across IV's and a V and also III. So the Model theory may be dead, but I also have no precluded it to be a specific option group either. More to come, but thought this may be a good place to try and "Self Evaluate".

Thanks again!
Bob

 

RechealSeven,

Based upon PUGSY's comment:
"Today when the grabbing happened I was in quite a hurry, so probably didn't wait at all. "

I just think it interesting...nothing against you Pugsy just trying to get more info to make some rationalization to the issue...But that was helpful and honesty is good!

 

The more info the better, I say. I'll have to note how long I waited if it happens to me again.

 

The hurry theory certainly has some intuitive appeal... reasonable theory. The problem is, I pretty much always do the same rushed exit and it's only done it the one time. It's not that I'm actually in a hurry, but there just doesn't seem to be any point in waiting, so I just go. So in my case, the absence of the behavior wouldn't prove anything... would only disprove the theory if it did happen again. Some other posters seem to be having the issue more frequently though, so perhaps someone who has it weekly or more could try out the suggestion and see. At least we're working on the problem with some good old fashioned collaboration - thank you Bobsprius!

 

I've onky experienced grabbing brakes once in 2500 miles. I almost always put it in gear and go as soon as the "ready" symbol appears. After all, isn't that what ready means?

 

I have only had this happen once. We stopped at a store, the wife went in to shop and I left the car "on". We sat about 12-15 min. Backed out of our spot (level parking lot) and it happened. We previously traveled about 30+ miles before getting to the store (the car was warm and certainly no RUST on the rotors ).

At this point I am not worried about it but it sure would be nice if it was diagnosed.

 

Without reading all 11 pages, I'd have to say it happens on most cars, but is more noticeable on the Prius. For one, it's extremely light, and now has 4 wheel disc brakes. The regular brake wear-in is in the forward direction, and when you go in reverse and tap the brakes, it is creating friction with the pads contracting on the rotor which is going in a reverse direction. Being a lighter car, it doesn't have the same momentum to overcome and overwhelm the slight braking. That's just my theory.

 

quote=brad_rules_man;961718]Without reading all 11 pages, I'd have to say it happens on most cars, but is more noticeable on the Prius. For one, it's extremely light, and now has 4 wheel disc brakes. The regular brake wear-in is in the forward direction, and when you go in reverse and tap the brakes, it is creating friction with the pads contracting on the rotor which is going in a reverse direction. Being a lighter car, it doesn't have the same momentum to overcome and overwhelm the slight braking. That's just my theory.[/quote]

Yes, but why does it happen intermittently??

 

Theories formed without at least a review of the available data are highly unlikely to be of much use. But that's just my theory.

 

My car is approaching 7000km and recently this problem has happened to me twice.
Something to think about:
The emergency braking system that automatically puts the brake on if it calculates the car is going to hit an object while driving forward, may have something to do with it. If somehow this feature were to switch on and sense an object in front of the car it would produce the symptoms that posters have described.
For the brake grabbing to happen while in reverse would require a software fault in a computer.
Does anyone know if one or more computers would need to be involved?
1. The computer system would need to sense the car is incorrectly in forward motion.
2. The computer system would need to sense the radar has sensed an object close to the front of the vehicle (quite likely).
3. The computer system would need to only respond when the brakes are being applied.
If more than one computer would need to be involved the less likely it is being caused by a computer problem.

 

Well, ... I was responding to the original post, in which all or most of the original data was in. The only problem was I didn't have time to read all the other responses... and I think that the first post pretty much reveals the problem, I was just theorizing on why the Prius is more vulnerable to the obvious problem. Sorry if that somehow bothered you.

In reply to the preceding post, It happens intermittently based on external conditions. I.E. rain, high humidity, driving conditions, car wash, wtv.

 

Does anyone have this issue think it might be the Gas motor kicking in, because I have had this problem and that's what it feels like, i'm backing up and it's clearly in EV mode (meaning I can't hear the engine) and I get all this rattle and back grabbing about the same time the motor kicks in.

 

If that is the cause then there is a design fault. The motor coming on should not affect the brakes.

 

I'd like to add an observation that I don't think has been mentioned. First, just to settle the questions that seem to keep coming up, this problem has occurred for me either 3 or 4 times (can't remember for sure), I have 4000 miles on my car, that the most recent occurrence was a few weeks ago. Each time it was on a basically level surface, either my driveway or a parking lot.

Here's the part I don't think has been mentioned before, and it's kind of hard to describe. The first time I touched the brake, I could feel resistance (a firmness) in the brake after a very short push. After that, the resistance seemed to rise at each touch of the brake, until at about the 3rd or 4th touch, the resistance started immediately. If I had to come up with an analogy, it was like something was coming up to meet my foot as it pushed.

What I'm trying to convey is that the behavior of the brake pedal is very different from what I normally experience. After the first time, when it came as a total surprise, I was able to recognize the other occurrences at the first touch of the brake.

 

You know, I honestly didn't take note of the pedal behavior - I suppose I was too surprised by it all. But that is a great observation and if it ever happens to me again, I will definitely remember to take note of the pedal.

 

I don't think I have the above described system on my trim level II, so that wouldn't be the problem in my case.

 

I would agree with this as when it happen to me, a fly could have touched the pedal and the wheels would have locked up. With that said, perhaps an over-active brake assist glitch? Nah, not entirely because one thing I also noticed is that the way the car braked... it seemed like one or the other set of brakes where applied not both (front and rear). It felt entirely different than normal braking.

Peter