Leaf Brake Problem, pedal going to the floor

2014 Leaf, 66k miles, no brake issues until now.

Went to brake and noticed a slight more pedal movement without braking. More movement on the brake pedal and the car stopped. Then noticed that with additional force, the brake pedal went to the pedal stop. Turned off the master switch and on again and it seemed better but this could have been from cycling the pedal up and down. Drove round and the car did stop correctly, but after pressing on the brake pedal to stop the car additional pressure would make the pedal go completely to the hard stop on the pedal.

I am not sure if this is normal or not because I don't remember every pushing the pedal that hard before, only enough to stop the car. There are no warning lights and no codes on LeafSpy. I am an aircraft, auto, and everything else mechanic so my experience tells me that there is air in the fluid system. The brake fluid is at the top full mark and there are no leaks we can find.

Could someone try to press their Leaf brake past firm and see if it goes to the hard pedal stop and report back? A force measurement shows 40 pound of force to go to the hard stop. Do difference on mine but try with the car off and on. Looking on this post, https://www.mynissanleaf.com/viewtopic.php?t=30566&start=50
page six about half way down, there is a cross section of the master cylinder with the electric motor boost and a description of the operation. In looking at the scross section, it looks like with no power, the brake pedal should still "firm up" upon compressing the fluid in the master cylinder.

Thanks!

Bled the brakes and changed fluid. No air in the lines. Same issue, pedal seems normal until pushed harder than 40 pounds and then it goes to the floor. I'm now thinking it is the master cylinder. It feels the same with car powered on or off. The brake master cylinder looks as if it can be replaced and not the whole boost unit. Does anyone know if this is so?

It's hard to say if your car's braking is normal without actually examining it, but it's always been the case for me that I can push the pedal past the initial resistance, all the way to the mechanical stop.

40 lbs sounds accurate. It's a very complicated system that blends friction braking and regenerative braking -- a fly-by-wire system. The Brake System section of the service manual is over 500 pages. That doesn't include the "Brake Control System", which is another 160 pages.

Hi, Thanks for replying. So you can press the pedal past initial resistance and then it takes about 40 sounds to press it all the way to the floor? Maybe nothing is wrong with my brakes.

DungenessLeaf said:

Hi, Thanks for replying. So you can press the pedal past initial resistance and then it takes about 40 sounds to press it all the way to the floor? Maybe nothing is wrong with my brakes.

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Yes, it's quite a long throw after the brakes are engaged, to the mechanical stop near the floorboard. The resistance doesn't change; it's not like a conventional master cylinder where pedal movement is limited by the incompressibility of the fluid. The brake unit uses a stroke sensor to determine how much braking you are calling for. Of course if your brakes seem to be behaving markedly different than they used to, more investigation would be warranted.

That is interesting and I would like another comparison. Can someone else check and see if they can push the brake pedal all the way to the floor? Takes about 40 pounds after it firms up.

This morning I just remembered that there was someone the works a mile away with a leaf and I drove over there and asked her if I could feel her pedal. It does exactly like you said and exactly like mine. Press on it with car on or off and it firms up and then with about 40 pounds will travel all the way to the stop on the floor. Sorry for questioning you but it now appears that this is normal feel for the brakes on a Leaf.

And you may have also invented a somewhat impertinent pickup line, as well.

LeftieBiker said:

And you may have also invented a somewhat impertinent pickup line, as well.

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Seems like more than a bit of a stretch too, doesn't? 40 lbs, really? Exaggerate much??

Yea, she got a giggle out of that too. No exaggeration. I measured it with a force gauge. A press of 40 pounds pushed the pedal to the floor, 30 pounds does not.

DungenessLeaf said:

This morning I just remembered that there was someone the works a mile away with a leaf and I drove over there and asked her if I could feel her pedal. It does exactly like you said and exactly like mine. Press on it with car on or off and it firms up and then with about 40 pounds will travel all the way to the stop on the floor. Sorry for questioning you but it now appears that this is normal feel for the brakes on a Leaf.

Click to expand...

I get it. It was alarming for me too the first time I noticed it.

If you feel the pedal travel carefully, I think you will find that the hard (mechanical) stop you feel is actually the resistance of the fluid not being compressible after the pads are in firm contact with the rotors--the same as conventional brakes when power assist is not working. The pedal feels like it is hitting a mechanical stop (or the floor), but it really is not. I had an intermittent CAN Bus communication issue with the intelligent brake controller (master cylinder with hydraulic servo assist) of the 2015, but the hydraulic brakes would always stop the vehicle without power assist from the controller if the pedal was pressed hard enough after going through the normal travel of the master cylinder. It felt like the pedal was going to the floor even though it was at least 1/2-inch above the floor with the brakes fully applied.