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Re: Grabby Brakes?

Posted: Mon Mar 16, 2020 2:04 am
by kicker
The brake recalibration had no effect but replacing the 12V battery improved it immensely, the modulation on regen can be a little jerky on occasion but there is no more awkwardly lurching to a halt when moving slowly in traffic, very happy with how it is now :D

Re: Grabby Brakes?

Posted: Mon Mar 16, 2020 3:16 am
by LeftieBiker
kicker wrote:
Mon Mar 16, 2020 2:04 am
The brake recalibration had no effect but replacing the 12V battery improved it immensely, the modulation on regen can be a little jerky on occasion but there is no more awkwardly lurching to a halt when moving slowly in traffic, very happy with how it is now :D
Interesting observation. I wonder if the 12 volt battery, if weak, acts as an intermittent resistor in the braking system, throwing off the responses of the brake booster by lowering the system voltage under some conditions. Given the large number of older Leafs with 12 volt battery issues, this bears further investigation...

Re: Grabby Brakes?

Posted: Tue Mar 17, 2020 4:08 am
by kicker
My 12V battery was the original Japanese item fitted back in 2013, the voltage was fine and the indicator shows as healthy but I bet it wouldn't perform well if load tested, have seen it a lot on ICE vehicles except it's more noticeable as the vehicle won't start :D

I see there is a servo that controls the hydraulic pressure according to an algorithm and acts as a booster (instead of engine vacuum), it's as though this pressure suddenly spikes causing the grabby feeling.

I still get a little bit of the grabby feeling occasionally but it's no longer at the crawling speed which would cause the vehicle to jerk to a halt which was very annoying for me and any passengers.

Re: Grabby Brakes?

Posted: Sat Mar 21, 2020 8:27 am
by nlspace
There are so many stories such as yours here on the forum of strange problems and issues that are caused by an weak, old or worn out 12V aux battery.

i suspect that the grabby brakes on the second press of the pedal occurs with a weak aux. When the pedal is first pressed it causes spooling of the actuator motor forward to increase the hydraulic pressure, but then when the pedal is released there is not enough voltage left in the system (aux + big black capacitor) to drive the motor back to the home position. When the pedal is pressed the second time the hydraulic system is already highly pressurized such that even the smallest pedal travel causes a massive lock on the calipers.

One test of this might be to remove the fuse for the capacitor and test drive the braking action.

Replacing the aux battery is the same as for an ICE car, remove negative terminal first, then positive. Install positive first, then negative.