Power Brakes

[gncndad]

Agreed. I'm just leery about leaving brake fluid in for 4+ years, as some here have stated. I'd wager a lot of money that the chemical composition of the fluid at the caliper is, in a word, dangerous, while at the reservoir, it might very well look fine. Not sure if the test strips pick up the nastiness so far from the calipers.

[LeftieBiker]

Agreed. I'm just leery about leaving brake fluid in for 4+ years, as some here have stated. I'd wager a lot of money that the chemical composition of the fluid at the caliper is, in a word, dangerous, while at the reservoir, it might very well look fine. Not sure if the test strips pick up the nastiness so far from the calipers.

I think 3 year fluid flushes are reasonable. I had one done on my 2013, in the 5 years I leased it.

[Oilpan4]

If you don't bleed the brakes for a few years and then you go to do it, guaranteed you will get black brake fluid out for the first few pumps.

[GerryAZ]

One reason for more frequent brake fluid changes on the LEAF is regeneration only works when the battery is partially discharged. On a long downhill run, regeneration may become insufficient to help slow the car so the friction brakes must be capable of keeping speed down. If the brake fluid has moisture in it, the moisture will boil as the brakes get hot. This will cause brake fading or worse. Since oil floats on water, moisture in the brake fluid will tend to collect at the lowest points in the system (which are the calipers). This makes it more likely to boil that moisture on long downhill runs. By recommending annual (or every 2 years) brake fluid replacement, Nissan minimizes their liability for loss of braking due to moisture in the fluid.

I generally have the brake fluid replaced every two years when doing the annual battery check because my dealer offers me a discount. The price my dealer offers is low enough that I would rather let them do it than go to the trouble of doing it myself. Even in my dry climate, I notice a difference of pedal feel after brake fluid replacement (pedal is firmer with new fluid).

[gncndad]

GerryAZ: I know we're flogging a dead horse with this, since those of us posting seem to agree that 2-3 years brake fluid change is safest.

I'm wondering about your comment about Nissan and liability. I know VAG products recommend a 3 year brake fluid change, which I've always respected. Is the Nissan Leaf braking system design different than other vehicles, and is the moisture you discuss greater than in any conventional hydraulic system? I should think 2 years is still overkill, based on...ahem...44 years of auto maintenance.

[GerryAZ]

GerryAZ: I know we're flogging a dead horse with this, since those of us posting seem to agree that 2-3 years brake fluid change is safest.

I'm wondering about your comment about Nissan and liability. I know VAG products recommend a 3 year brake fluid change, which I've always respected. Is the Nissan Leaf braking system design different than other vehicles, and is the moisture you discuss greater than in any conventional hydraulic system? I should think 2 years is still overkill, based on...ahem...44 years of auto maintenance.

I think the brake fluid in the LEAF, like many modern cars, is slightly more prone to moisture absorption because the reservoir has a vent. Older cars had a flexible rubber membrane that allowed for expansion/contraction of fluid with temperature change and pad wear without letting outside air reach the fluid. Two years is probably more frequent than needed, but other vehicles I have owned also called for service at 2-year intervals. I don't think the electro/hydraulic power unit and ABS system in the LEAF are any more prone to moisture damage than conventional vacuum booster master cylinder systems, but think about what happens with a LEAF on a long downhill run with a full battery charge. A gas or diesel car can be slowed down by downshifting if brakes start to fade (may cause damage to engine or transmission, but still possible in emergency). If the battery charge level/temperature/condition does not allow regeneration, there is no way to slow down an electric car without using the friction brakes so brake fade is more serious.

[Oilpan4]

Wah?
About 99.8% of Brake fluid isn't "oil". It's ether or polypropylene glycol and is very hygroscopic.
It gets wet because water diffuses past or through the brake caliper seal and mixes with the brake fluid. Water plus glycol makes a homogeneous mixture that still has a pretty high boiling point and that's what you want.
If you use hydrophobic brake fluid like a silicone based brake fluid and water does get past the seal it will separate out in the caliper you get little pockets of water trying to boil at much lower temperature. The water will also freeze at normal temperatures.