braking in reverse

This happened to me 3xs this week. All events happened while either sitting in the car and restarting. Once when I got out and back in quickly. I had passengers in the car on one occassion. They thought I was joking. Felt like a complete idiot.

 

If you can find a startup sequence that reasonably-often "causes" this backup problem, please let us (at least me) know.
Thanks

 

I wonder if this could really be two effects?

First, I've noticed that the brakes are very sensitive when in reverse. Nothing really wrong in my opinion, just as long as you're used to it.

I've experienced the second effect a couple of times, where there seems to be too much torque when the car is first put into reverse. It reminds me of a regular automatic transmission when put into gear if the engine is idling too fast. The system will "thunk" into gear and lurch if the brakes aren't on. In the Prius, when the driver feels this lurch he/she over-applies the brakes and since they're sensitive in the first place, the car bangs to a stop.

Now, why would it lurch at intermittent times? Could it have something to do with the ICE startup? MG1 supplies the torque to spin the ICE, but some of this torque will also be sent to MG2 via the PSD as well. Since MG2 is directly geared to the drive axles, if back torque isn't applied via MG2 there could be a lurch sent to the wheels. If this is the case, the lurch is due to the inertial load of the ICE being spun up to starting RPM, so this should only be a lurch rather than a continuous "runaway" situation. I'm not sure why this isn't seen when going forward, maybe the "lurch" is always in the reverse direction? So when going forward, the lurch would act "against" the forward torque being supplied by MG2. When in reverse, the lurch would be "added" to the MG2 torque, giving a much more apparent jump?

So, this is just a hypothesis, but I'll be watching now for the lurch to see if it fits. If true, it should only occur when the ICE is started automatically right around the time when the driver shifts to "R". Before the shift to "R", the lurch would act against the parking pawl and not be noticed. If the ICE is started while the car is actually moving in reverse, the effect may not be as noticeable.

 

Since I have still NEVER experienced this, and over 3K miles now, I suspect it's as you stated as well, some sequence of events.

The event could be as simple as putting in Reverse "very quickly" after start....

We just have not pinpointed the right combination.

I always start my car and wait for the ICE to start and then shift into Reverse.

It may be as simple as some combination which is causing this..if we could pinpoint it now?

 

OK, i confirmed that backing while the ICE starts doesn't trigger the surge, at least on my vehicle. I started backing up a slight incline and waited for the ICE start. It was nice and smooth with no lurching. So maybe the problem occurs if you go into "R" at exactly the same time the ICE starts? That will be harder to test.

 

I noticed this today while backing up on flat ground. I touched the brakes lightly and the car slammed to a stop. It happened over and over until I stopped and pumped the brakes.
When I pumped the brakes, the pedal fluctuated between very stiff and very soft.

This is not normal. There is a lot of talk and "me too" posts about this for 5 months 17 pages. What exactly does it take for Toyota to notice there is a problem and fix it?

 

Join the club! In order for Toyota to do something about it, they have to know about it. I suspect by now they do but if you have not reported to the dealer or Toyota directly, do so. I did it through the survey they sent out.

 

I have only had this happen once, that I recall, and that was a forward motion. It was right after I picked the car up, (new), and I was stopped in a convienience store. When I pulled out, (forward), I noticed a car coming in my proliferal vision, I was only moving 1 or 2 miles per hour, and at the time just thought I reacted too suddenly, but later thought, no the brakes just like grabbed. The stop was so sudden my wife and I were both glad we had our seat belts on! I have not noticed the simptum in reverse, but will watch for it now. I just figured it was new, the brakes were not broke in------. And that may be the reason, but will watch for repeats.

 

Here is what I experience. When I start the car (foot on brake, push start button), put the car in gear (forward or reverse), then start to move slowly with my foot still on the brake (as you would if you were in a slow-moving line going forward, or slowly backing out of a parking spot) then the brakes are grabby.

However, if I start the car (foot on brake, push start button) then take my foot off the brake, then re-engage the brake to put the car in gear, the brakes behave normally. This happens every time. As long as I remember to take my foot off the brake, then back on to put the car in gear, the braking is fine.

I first noticed this when I was stopped, with the engine off, in a ferry lineup. The lineup is on a hill, so the car was pointing downhill towards the ferry. As the cars started to board the ferry, I would start the car and put it in gear, with my foot still on the brake. The line moved slowly, so I kept my foot on the brake as we inched forward and downhill, never fully releasing it. Once the brake was fully released then re-engaged, there was no problem.

This behavior is the same whether you are on a hill or not. But in this case, because I was on a hill, I did not have to fully release the brake to step on the gas pedal, because the car was rolling downhill on its own.

And again, fully releasing the brake pedal and then re-engaging it before putting the car in gear always resolves the problem for me.

 

Even if that works, it is a workaround to avoid triggering the problem. It doesn't resolve it. It shouldn't happen anyway.
Resolving it will require Toyota to fix the issue so you don't get the grabby brakes no matter what sequence of pedal pushes are done.

 

That's true, but in the meantime you can avoid the problem by releasing the brakes and re-engaging them before putting the car in gear, forward or reverse. And to make it clear, it only happens when the car is first started, so you only have to take your foot off the brake once, after you start the car, not every time you brake.

This was not an issue with my Gen 2 Prius.

 

FYI. Mine does not do that, and that's my normal practice.

 

Add my car to the list of cars with "grabby brakes" when in reverse. I had 3 people in the car, also Prius owers, when backing out of the driveway it slammed everyone into the back of their seats (repeatedly). I don't remember if the ICE was on or not but the engine was already warm, so probably not. I just stopped the car, put it in park, turned it off, then started it up again. After that, everything worked fine. I'm going to bring the car in for service in a few miles, so I'll ask the Service Manager to check if there are any error codes in the system. My car was built in April 2009.

 

Had it happen again a few days ago. The first time I had 1400 miles now I have 4700 miles on the car. Backing slowly out of the garage on a very slight incline. No mater how lightly I touched the pedal it would very abruptly stop. I am not saying pressed the pedal, I mean touch, and the brakes seem to lock up. Put it in park, pressed the pedal firmly and when put in reverse the problem is gone.
I have talked to two dealers and they say they have never heard of the problem. They want me to bring it in when it is doing it. I don't seem to be able to get the car to duplicate the problem. The dealers see so many people issues they are difficult to convince there is a problem unless they see it. Even if they do notice it if it is intermittent they don't look very hard for the problem. Probably get flat rate pay.

Barn

 

Because of that, we need to contact Toyota directly about the problem instead of through the dealer. I marked it down on my survey card they sent out.

 

Went to dealer today, they said they spent several days trying to find the problem on one of their cars. Found it to be normal even on the slightest slant. They think it is normal,that the brakes lock up, well why dosn't happen every day then?

Barn

 

Today, I put the car in reverse and hit the brakes. The brakes really grabbed and felt weird. I did not like that at all.

 

Strange...I don't know what to tell you guys. I have 25,600 miles on my 2007, and have never had any problems whatsoever with my brakes, forward or backward. Perhaps this problem is unique to the 2010 model?

 

That could certainly be the case...

 

My 2010 is smoth in reverse but I noticed there's no regen, OTOH, I probably wasn't going fast enough..