Power Brakes

I haven't noticed the grabby/numb thing yet. I can feel the transition from regen
to hydraulic, but it's smooth enough for me and not a bother. I do approach stops
gradually, though, and that might make a difference.

I did notice something a day or two ago. I was approaching a stale green light that
turned yellow shortly before I got to the stop line. I judged it safe to nail the brakes
and glanced over at the motor power gauge expecting to see massive regen. I saw
almost nothing. Apparently the hydraulics took over in that hard-stop situation.
There was nothing odd about restarting after, but I don't think I did any creeping.

Looking at the Service Manual, bleeding the LEAF is routine, there is nothing extra to
do for the ABS in the LEAF.

With ABS, it is best to use a power bleeder to insure that all the fluid in the ABS system is exchanged. This is pretty much standard procedure these days for a brake fluid change.

highcountryrider said:

Looking at the Service Manual, bleeding the LEAF is routine, there is nothing extra to
do for the ABS in the LEAF.

Click to expand...

highcountryrider said:

I did notice something a day or two ago. I was approaching a stale green light that
turned yellow shortly before I got to the stop line. I judged it safe to nail the brakes
and glanced over at the motor power gauge expecting to see massive regen. I saw
almost nothing. Apparently the hydraulics took over in that hard-stop situation.
There was nothing odd about restarting after, but I don't think I did any creeping.

Click to expand...

Just watch the regen gauge as you slow brake towards any stop.
It seems to cut out as you get down to very slow speeds.
There must be a reason they want to switch you over to friction brakes just before you stop.

The Leaf has conventional hydraulic brakes: master cylinder, four calipers and the booster/antilock/traction/stability control unit. This adds push depending on the regeneration, the pressure on the pedal. Rather than a vacuum assist reservoir the Leaf has a capacitor bank to provide emergency power assist.
Because of the lack of “engine braking” comparable to ICEengines with downshiftable transmissions, the Leaf depends more heavily on the integrity of the hydraulic brake system. For this reason the fluid change interval is 2 years (1 year in harsh conditions) rather than 3-5 years for conventional ICE cars. Further, the master cylinder and booster pump are very expensive to replace, so we don't want its life shortened by water contaminated fluid.

^^^
Seems like BS to me. My gen 2 Prius which I had for 13 years was just like this w/regen and a capacitor bank in the trunk area.

I don't recall crazy brake fluid change intervals or any at all. If I'd ever had the brake fluid changed, it was probably only once during the time I had the car. Will need to check w/the maintenance guide for my mom's 07 Altima Hybrid (based on Toyota hybrid synergy drive).

I do have a device to measure brake fluid moisture level and test strips to measure copper content. Both were fine on my '13 Leaf when I last checked a few weeks ago.

I suspect the silly brake fluid change intervals + the annual "required" battery check were bones that Nissan corporate threw to dealers to make up for other lost maintenance revenue (oil, spark plug, belt, etc. changes, throttle body and EGR cleaning, etc.)

I agree on the above about Nissan throwing their dealers some business. As for no engine braking increasing the stress on the brakes, that is more or less true only if you use Normal driving more. If you drive in Eco and/or in B or ePedal mode, you get plenty of regen braking.

AlGrsn said:

The Leaf has conventional hydraulic brakes: master cylinder, four calipers and the booster/antilock/traction/stability control unit. This adds push depending on the regeneration, the pressure on the pedal. Rather than a vacuum assist reservoir the Leaf has a capacitor bank to provide emergency power assist.
Because of the lack of “engine braking” comparable to ICEengines with downshiftable transmissions, the Leaf depends more heavily on the integrity of the hydraulic brake system. For this reason the fluid change interval is 2 years (1 year in harsh conditions) rather than 3-5 years for conventional ICE cars. Further, the master cylinder and booster pump are very expensive to replace, so we don't want its life shortened by water contaminated fluid.

Click to expand...

Isn't regen braking the OPPOSITE of the highlighted phrase??? I thought one of the strongest benefits of regen braking was to reduce the load/stress on the hydraulic system. 2 year fluid change? Maybe, if I lived in high humidity year round. I've settled on 3-4 years for all of my cars (hybrids/elec) precisely because the stress on the fluid is so low, and the humidity in the DFW is higher than I would like, most of the time.

As for pads/rotors, another "HAHA!" My 2014 Avalon pads are at 8mm all around, after 111k miles.

cwerdna: I'm curious about how you test brake fluid with test strips. Do you open the bleed valve and capture fluid at the end of the hydraulic line, or simply dip the test strip in the fluid reservoir? It's my understanding that brake fluid doesn't really circulate (return to the reservoir), so is dipping into the reservoir accurate?

Because the fluid in the reservoir is exposed to more air, and thus more water than the fluid in the lines, testing the reservoir is fine, because it's testing the "worst" of the fluid.

LeftieBiker said:

Because the fluid in the reservoir is exposed to more air, and thus more water than the fluid in the lines, testing the reservoir is fine, because it's testing the "worst" of the fluid.

Click to expand...

I'm not sure I'd agree. I'd think the fluid closest to the heat of the brakes (thermally challenged) would be pretty nasty, as well. I think of the reservoir as simply a holding tank for the system. I'm going to read up on this, because...I'm...OCD!!!

Go for it! Me too on the OCD. I'm just too tired these days to be good at it.

Look at it this way: sustained extreme heat likely does degrade brake fluid, but an EV like the Leaf sees little of that, relatively speaking. The damp air of a typical Fall or Spring coming into contact with the open reservoir adds water, while heat in the calipers generally doesn't. So it seems to me that the most deteriorated brake fluid would be in the reservoir, not in the lines or calipers.

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.

gncndad said:

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.

Click to expand...

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

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.

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).

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.

gncndad said:

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.

Click to expand...

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.

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.