Regenerative Breaking and Break fluid

I just bought my Leaf and had it inspected by the local Nissan dealership before sealing the deal.

Something that came up was that they recommended that I change my break fluid a little earlier than recommended because "regenerative breaking is a fluid heavy process." But isn't regen braking just reversing the polarity on the electric motors? Is there even ANY fluid involved in this process?

What I've found online confirms my suspicion that the service personnel were full of it, but I don't want to be wrong about it.

You are correct, and they are at best mistaken and at worst lying.

You're correct that regenerative braking is simply reversing the way the current flows. Nearly any electric motor can be turned into a generator by switching the electronics around so the mechanical energy is converted to electrical energy, rather than vice versa. The brake fluid has absolutely nothing to do with this and there is no heat generated at the wheel. etc.

Smells like the dealer trying to doop you.
At 80,000 miles my breaks are like new as far as wear.
Brake fluid is hydroscopic, which means it pulls in water like one of those "damp rid" dehumidifiers and needs to be changed every few years.

Thanks for the response!

Although regen is electrical, the car does need to "blend" the effect of both regenerative and friction braking. Thus the system is more complex than even a regular ABS equipped vehicle. Not that it wears out the fluid, but I've come around to the notion of 2-year flush intervals. Simply the expense of the braking components that could require replacement due to water/corrosion/contaminants dwarfs the expense of a fluid change by orders of magnitude.

Sure, you could get test equipment/strips, etc.. But really there is so little periodic maintenance that a 2-year flush seems the least bothersome and most certain method. And if you DIY it is very cheap insurance.

There is a downside to that 'cheap insurance.' The person doing the flush can screw up and get water into the system where there was none before. I don't get automatic transmission flushes every two years 'just in case,' and I don't advise that anyone driving a Leaf normally, in a normal climate, get the brake flush any sooner than three or four years. Getting your car serviced is also rolling the dice on getting it damaged.

LeftieBiker said:

There is a downside to that 'cheap insurance.' The person doing the flush can screw up and get water into the system where there was none before. I don't get automatic transmission flushes every two years 'just in case,' and I don't advise that anyone driving a Leaf normally, in a normal climate, get the brake slush any sooner than three or four years. Getting your car serviced is also rolling the dice on getting it damaged.

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I imagine you mean getting air into the system. You'd really have to go out of your way to get water in the system. And the point is to get water out; as mentioned the fluid is hygroscopic.

Nubo said:

LeftieBiker said:

There is a downside to that 'cheap insurance.' The person doing the flush can screw up and get water into the system where there was none before. I don't get automatic transmission flushes every two years 'just in case,' and I don't advise that anyone driving a Leaf normally, in a normal climate, get the brake flush any sooner than three or four years. Getting your car serviced is also rolling the dice on getting it damaged.

Click to expand...

I imagine you mean getting air into the system. You'd really have to go out of your way to get water in the system. And the point is to get water out; as mentioned the fluid is hygroscopic.

Click to expand...

Getting air in gets water in, in most climates.

LeftieBiker said:

Nubo said:

LeftieBiker said:

There is a downside to that 'cheap insurance.' The person doing the flush can screw up and get water into the system where there was none before. I don't get automatic transmission flushes every two years 'just in case,' and I don't advise that anyone driving a Leaf normally, in a normal climate, get the brake flush any sooner than three or four years. Getting your car serviced is also rolling the dice on getting it damaged.

Click to expand...

I imagine you mean getting air into the system. You'd really have to go out of your way to get water in the system. And the point is to get water out; as mentioned the fluid is hygroscopic.

Click to expand...

Getting air in gets water in, in most climates.

Click to expand...

The fluid is always in contact with outside air because a vent mechanism is needed to equalize pressure in the reservoir as the brakes are depressed and released. That's how water slowly accumulates. The short period of time when the cap is off for refilling during flushing and bleeding isn't a concern. I was referring to air in the brake lines, which will degrade braking since it is compressible and is removed by bleeding.

We aren't really disagreeing. Air in the lines will add more water than just the air at the top of the reservoir. Dealership mechanics make mistakes. For that reason, I avoid having a service done more often than it needs to be done. Every year or two for the Leaf, save maybe in a tropical climate, is more often than the flush needs to be done. This service interval was a sop to the dealers by Nissan, not dictated by the complexities of the braking system..

I chose to have brake fluid replacement done every other year along with the traction battery test on my previous LEAFs. I plan to do the same with the 2019 SL Plus. This meets the service requirements in the owner manual to keep the warranty intact. On both 2011 and 2015, there was significant improvement in brake pedal feel after each fluid replacement.