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TomT
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Re: Grabby Brakes?

Annual brake fluid change is dealer profit and nothing else but... There is no way that it has anything to do with brake grab... The only reason to change it is to prevent a lowering of the boiling point (reversible) and a possible increase in corrosion (non-reversible) due to brake fluid's hygroscopic propensity to absorb moisture. Neither of these would cause the grabby brake problem nor would simply replacing the fluid solve it.
ericsf wrote:Considering that I didn't notice the grabby brakes for the first 6 months I owned the car and the fact that Nissan is recommending brake fluid replacement on the LEAF 4 times more frequently than on other cars (15K vs 60K) I tend to think it's the later. What do you guys think?
Last edited by TomT on Wed Feb 22, 2012 4:15 pm, edited 1 time in total.
Leaf SL 2011 to 2016, Volt Premier 2016 to 2019, and now:
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ericsf
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Re: Grabby Brakes?

IBELEAF wrote:Still grabby for me post update...
Did you skip the fluid replacement?
SL w/ QC (3/5/2011) - 11bars on 1/23/2014 @ 54k miles - 10 on 12/23/2014 @ 73k - 9 on 10/5/2015 @ 85k - 8 on 7/3/2016 @ 96k
phxsmiley
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Re: Grabby Brakes?

And I don't think the issue would be related to brake fluid, since turning off the stability control definitely affects it. This is definitely some kind of controller problem.
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turbo2ltr
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Re: Grabby Brakes?

I've been noticing this more and more lately.

It gets into this "grabby" mode, especially coming to a stop, where it's damn near impossible to creep up a little without giving everyone whiplash.
I noticed if you completely let off and get back on, it resets this behavior and they are much more 'normal'.

I've also noticed some weird regen stuff. It's hard to know what's regen and what's brakes. I noticed something just today, if you apply the brakes very quickly, but not necessarily hard, they grab a lot more. i.e. releasing, then applying again more slowly, but to the same pressure, does not slow the car down as quickly.

I've been driving a bit more aggressively lately, so this may have something to do with why I'm noticing it more.. I think the grabbyness has to do with the speed at which the brakes are applied, and they stay grabby until you let up. But that's just a theory at this point..
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shtimseht
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Re: Grabby Brakes?

I too have noticed the grabby brake problem. Most noticeable at parking lot speeds. I press the brake peddle just a little to slow the momentum of the car down. Instead the brakes grab and stop the car to complete stop. It does it quickly enough that you and anyone ridding in the car jerks forward.

Annoying. Seems like NISSAN should look into this given the number of posts. I've had no issues of this while at roadway or highway speeds (>10-15 mph).
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Rokeby
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Location: Ballamer, Merlin

Re: Grabby Brakes?

Don't have a LEAF yet, but I am interested in all aspects of its operation.

Do have a Gen II Prius though, At times it has grabby brake issues.

Although I suspect that the LEAF condition is a software glitch, my Prius experience
might be applicable in some cases.

It has to do with damp brake rotors leading to a thin layer of rust on the rotors.
It usually happens after the car spends a night out with high humidity and cooling
temps leading to heavy dew --> rusty rotors in the morning. Applying brakes gets
a god-awful gritty, grinding sound, and serious grabbiness, especially at low speeds.

The fix on the Prius is to get up to a good speed, ~50+ MPH, on a stretch of road with
no other cars behind. Shift to neutral (no regen possible), depress brakes hard.
Repeat 2 or 3 times… all better.

I have never had the issue after driving home in the rain and then leaving the car sitting
overnight. I guess in this case the rotors have been swept clear by those last two brake
applications at less than 8 MPH -- 100% friction braking -- as I pull into the driveway,
then come to a stop.

FWIW
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gbarry42
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Re: Grabby Brakes?

I have done nothing to my LEAF, and I haven't noticed the grabbing lately :D But, really, a lot of you seem to be victims of accidental correlations as this problem comes and goes. BTW, Rokeby, I get this in the middle of my trip after I've driven all the surface streets to the freeway. There's a downhill approach to the on ramp with a traffic light. Plenty of opportunity for it to happen there. So it doesn't act like moisture or rust on the rotors, as it can happen at any time.
And there goes the first capacity bar! At 24,000 mi on 9/9/2013.
Second bar at 30,500 mi on 2/7/2015.
IBELEAF
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Location: Seattle, WA

Re: Grabby Brakes?

Grabby brakes symptom only appears while driving in very low speeds so it's not something I notice every day, but when it does happen I always wonder how it appears to the driver behind me who might think I am braking for him. :lol:

Also, I was never asked to replace brake fluid by the service tech and they never suggested I needed one besides I have my doubts that it would resolve the issue anyway.
Currently: '12 Volt (12k) since 7/2012
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SierraQ
Posts: 185
Joined: Mon Oct 18, 2010 8:44 am
Delivery Date: 02 Sep 2011
Location: Dallas, TX

Re: Grabby Brakes?

My theory is that this has something to do with a software bug that only occurs when the "brake on" signal is present for an extended period, like when you ride the brake in stop-and-go traffic. There is software somewhere that is taking brake pedal pressure with other inputs and determines a mix of regen and physical braking apply which includes the intensity. It is the physical intensity level that is getting out of bounds rising to such a steep curve vs brake pedal pressure that it loses all semblence of smoothness. There may be some variable that keeps growing due to the bug. Then when the brake is released the software likely clears all variables hence correcting itself.

This is the only thing that makes sense to me but i can't prove it without the CAN monitors that other people seem to have.

If I did have a monitor I would run a very controlled experiment where i tried braking in various ways to establish a baseline profile and then replicate the grabby state. I suspect we would see one of those CAN numbers shooting into the sky. If we could show this to Nissan maybe they could fix it. Of course why they are not investigating this in light of the potential safety issues is odd.
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TEG
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Re: Grabby Brakes?

I have written about this a few times over the past year, in other topics, but here is some more...

I think it is related to the "Brake Assist" feature in the LEAF.
I think it may be activating "Brake Assist" in some situations where we don't expect it.

Before ABS, they use to teach people to "pump the brakes" to avoid a skid with hard braking.
Even though ABS does that for you now automatically, some people are trained to pump the pedal when they do a panic stop.
I think the LEAF is trying to say "Oh, I see what you are trying to do... I am smarter than that - you want full braking now, and I have ABS so I will turn your pumping / pulsing action into an ABS assisted hard braking event."

What I have observed is that short quick "stabs" at the brake pedal, even if they only push it part way down can cause it to go into some sort of automatic braking mode.

Something like what they show in these videos:
"Even if you step on the brake lightly, you get maximum assistance..."


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