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Re: Power Brakes

Posted: Wed Dec 01, 2010 2:28 pm
by garygid
Perhaps this brake dragging and the resulting heating is the reason that "frequent" brake-fluid flushings are specified in the LEAF maintenance manual?

Re: Power Brakes

Posted: Wed Dec 01, 2010 4:33 pm
by wgs1912
garygid wrote:Perhaps this brake dragging and the resulting heating is the reason that "frequent" brake-fluid flushings are specified in the LEAF maintenance manual?
It is not going to drag the brakes through regen switches from 100% mech. to 100% regn back to 100% mech. With a variety of % inbetween each. The longer the time slowing I assume the longer it will stay in regen.

As far as brake fluid services it is for moisture and copper in the fluid not just heat. This site has some good info on brake fluid.

www.aa1car.com/library/bfluid.htm

Re: Power Brakes

Posted: Thu Dec 02, 2010 2:32 pm
by Norway
For what it is worth, the VW Golf Citystromers have a vacuum pump providing vacuum (can you provide vacuum ??? ) to a completely standard brake servo.

Diesels also don't have a natural vacuum in the inlet manifold, and have to have a vacuum pump. Normally this is mechanical, but on some diesels (e.g. some Volvos) they use an electric pump.

Re: Power Brakes

Posted: Thu Apr 14, 2011 9:21 pm
by Stoaty
Now that the Leaf is out, can anyone tell me how much regen is applied with slow braking (not using ECO mode), and whether this is a reasonable alternative to ECO mode? Do you see as much regen using the brakes as you would using ECO mode starting at same speed and using same rate of deceleration?

Re: Power Brakes

Posted: Wed Sep 28, 2011 11:24 am
by TEG
The topic of peculiar "brake assist" behavior was discussed elsewhere, but I can't seem to find the thread.

Anyways, I continue to notice a slightly odd inconsistency in the brake pedal action at very low speeds.

A typically scenario is like this:

I am pulling up to a stop light, using the brakes to slow down gradually and get ready to come to a stop behind the car in front of me. As I am doing this, the cars in front bunch together a little more closely so I ease back off the pedal a bit to "roll" forward a bit more, then ease back on... But now it seems to "grab" and slows me down suddenly (but just from like 5mph to 1mph), so I back off the pedal again since I wasn't quite ready to stop... Now this time the brake pedal seems numb, and I have to push it a lot harder than before to finally come to a stop.

When starting out slowly from a stop and "feathering" the brake pedal it seems OK. It is more when I have just slowed down a bunch (from say 40mph) and then try to modulate the pedal carefully to get into position that I find that pedal can sometimes seem overly grabby or overly numb.

I guess I attribute this to the "brake assist" function turning off or on.

http://en.wikipedia.org/wiki/Brake_Assist" onclick="window.open(this.href);return false;

It seems like it is turning on in some cases which are no where near a "panic stop" situation.

Re: Power Brakes

Posted: Wed Sep 28, 2011 11:34 am
by EVDRIVER
wgs1912 wrote:
garygid wrote:Perhaps this brake dragging and the resulting heating is the reason that "frequent" brake-fluid flushings are specified in the LEAF maintenance manual?
It is not going to drag the brakes through regen switches from 100% mech. to 100% regn back to 100% mech. With a variety of % inbetween each. The longer the time slowing I assume the longer it will stay in regen.

As far as brake fluid services it is for moisture and copper in the fluid not just heat. This site has some good info on brake fluid.

http://www.aa1car.com/library/bfluid.htm" onclick="window.open(this.href);return false;

That is not the reason for more frequent changes over other cars, it is because of the design of the LEAF electronic brake system and the added stress to the fluid. THe system is not like a traditional system and that is why it requires more frequent changes. All systems are subject to the same environmental issues.

Re: Power Brakes

Posted: Wed Sep 28, 2011 12:08 pm
by TomT
I don't believe this to be true. The actual braking system is a completely standard hydraulic and ABS system, and should see no more stress than any other such system, EV or not. The only real reason for brake fluid changes in street vehicles is because brake fluid is hygroscopic and absorbs moisture. Assuming that the system has not been abused and the fluid boiled, we change the fluid every two years or so because of this to prevent the moisture from lowering the boiling point of the fluid and, more importantly, causing corrosion of the brake components.

There is nothing in the design of the brake system in the Leaf that requires a yearly change. I simply see it as a profit mechanism...
EVDRIVER wrote:That is not the reason for more frequent changes over other cars, it is because of the design of the LEAF electronic brake system and the added stress to the fluid. THe system is not like a traditional system and that is why it requires more frequent changes. All systems are subject to the same environmental issues.

Re: Power Brakes

Posted: Wed Sep 28, 2011 12:19 pm
by davewill
TEG wrote:...I am pulling up to a stop light, using the brakes to slow down gradually and get ready to come to a stop behind the car in front of me. As I am doing this, the cars in front bunch together a little more closely so I ease back off the pedal a bit to "roll" forward a bit more, then ease back on... But now it seems to "grab" and slows me down suddenly (but just from like 5mph to 1mph), so I back off the pedal again since I wasn't quite ready to stop... Now this time the brake pedal seems numb, and I have to push it a lot harder than before to finally come to a stop. ...
Yep, I get that quite often. I've learned NOT to creep ahead in those situations, but just sit still. Only completely releasing the brake seems to clear it, and since I'm stopped at a light, I can't do that.

Re: Power Brakes

Posted: Wed Sep 28, 2011 12:40 pm
by Volusiano
When it comes time for brake service (fluid change, pad change, rotor turned, etc), I wonder if you can take the Leaf to any normal brake shop, or whether you should stick with Nissan dealerships for brake service.

Re: Power Brakes

Posted: Wed Sep 28, 2011 12:42 pm
by TomT
Anyone who is used to bleeding ABS brake systems can do the fluid change. The rest is standard old disk brakes that anyone who does brakes can also do.
Volusiano wrote:When it comes time for brake service (fluid change, pad change, rotor turned, etc), I wonder if you can take the Leaf to any normal brake shop, or whether you should stick with Nissan dealerships for brake service.