Car 'slips' when braking.

This is what others have reported and presumably what the update is suppose to fix. See if you can reproduce it and take the tech for a ride.

 

All cars I've ever had and driven fitted with ebd (from cheap city cars to out and out supercars) all do this to some extent.

The bumpy surface causes the rears to lock for a fraction of a second. This is very bad as it can make the car very unstable under braking. This is what the ebd is trying to sort out by cutting braking force to the rears using a valve. This changes the way the pedal feels and can often feel like the brakes have failed or a big clunk like you describe.

 

A software update can't fix physics. Bumps will cause a loss of braking action. The new 'fix' improves the sensation, but bumps can still interfere with braking.

Tom

 

Yep - nothing really to do with the hybrid. If you had a car without abs you'd feel the car lurch a bit (or even start to spin if there was any steering input or camber).

Even with abs on it's own a spin caused by locked rear tyres can happen too quickly for the abs system to react. This is where ebd cuts in to prempt the rears locking by cutting the rear brake force.

A good test is to find a suitable bumpy bit of road where this happens and when it's safe and quite brake enough to trigger the ebd then as soon as you feel it press the brakes hard. Guarantee you'll stop fine and fast without further drama.

 

Skipping is normal, but not because it is a hybrid. It happens because of the bumps. Without ABS you lurch and lock the brakes, with ABS you get a brake 'drop-out' sensation.

Tom

 

Common sense should tell you that what the current Prius does when braking over uneven pavement is different than other cars with ABS. ABS has been common for 20 or more years and the type complaints generated in significant numbers by the Prius have not occurred at nearly the same level with other cars.

Experience also tells me the Prius reacts differently under those conditions. Having driven numerous ABS equipped cars and also having taught behind the wheel high school driver education for 7 years, I can state without question that the release of the brakes that occurs with the Prius is more pronounced than any other car I have driven. Is it dangerous? Probably not. But it is disconcerting and does not give one a secure feeling about the Prius braking system and is the reason for the consumer complaints.

 

Our Prius was manufactured after the fix was implemented on the line, so I have never experienced the braking issue that many people have...
However, when I am lightly braking while going over bumps, the brakes will suddenly increase in force, usually jolting the car to a stop when I don`t really want to fully stop and have not applied more brake pressure.
I figured that this was the "fix" in action - better to increase in force than decrease, I suppose.

I am wondering if there is some difference in behavior between the fix on the line and the fix afterward.

 

What do you want, conventional braking system or the regen system? Get used to it

 

I was worried the fix would cause an over compensation like it seems you have felt. But like you said, probably better to have more braking than less. I still have not had my update done because I like the way my brakes work now. I will eventually though.

 

I wonder if having smaller tires makes it more noticable on the prius? I would think the smaller the area touching the ground the easer it is to loose traction. Maybe thats why it is more of a problem in the prius. I had a impala and the tires on that car have about twice as much rubber in them than the little ones on the pri.

 

yea they should've just put 17's for all the prius's and make it standard. I think the brakes are pretty bad for a light car. I'd rather not have regen as long as the brakes work better. I have to press brakes harder than i do on my 2 ton range rover

 

It is more pronounced because of the transition from regenerative braking to friction braking. The cause and effect, however, are identical to that of any ABS equipped vehicle, except for a minor change in braking effort as the car transitions from one system to another.

Tom

 

IMO this is exactly waht the recall was about.
I felt it before I brought my car in but not since.

 

Prior to the software update/fix, I experienced (once) the same sensation you described. So far, after the software update, I have not had any similar incidents - that was about 3 weeks ago. Did the software fix this sensation? Probably too early to say for sure, and I'd be willing to bet that unders some circumstances, I'll feel it again. But it really doesn't bother me, now that I know what to expect...

 

I think you used the wrong word there. If it was a change in effort the driver could compensate for it. The change is in effect.

 

The driver *can* compensate for it, simply by pressing harder. That's all there is to it.

Tom

 

If we are talking about that second or so when the system is moving from regenerative to normal braking on a rough surface I disagree because I've tried it. It doesn't change the amount of "slippage". If you do increase braking pressure during that time it does throw you forward against the seat belt when the transition is complete. Not the same thing at all.

 

If ABS braking is activated you will feel slippage. This is because of a loss of traction. If it is just a transition to friction braking, the difference in braking effort can be modulated by the driver.

Tom