Turned car off whie coasting in neutral and brakes locked. Why?

[Sparkatuz]

I own a 2004 Honda Civic EX, 4cyl, 127HP manual transmission--just in case it matters.

I recently read on the "201 Tips To Save Gas" that you can switch to neutral, turn your car off (not all the way, but to the point where the engine is off and the dash lights remain), and that it will save gas while coasting for long periods of time.

I tried it while using my brakes sparingly and they worked fine. Although bout 3 miles down the road I started to lose brake pressure, the pedal became near impossible to push down, and then I lost my brakes all-together. I quickly started the car and they came back. Why did this happen? Did I do something wrong?

[mini-e]

Originally Posted by Sparkatuz

I own a 2004 Honda Civic EX, 4cyl, 127HP manual transmission--just in case it matters.

I recently read on the "201 Tips To Save Gas" that you can switch to neutral, turn your car off (not all the way, but to the point where the engine is off and the dash lights remain), and that it will save gas while coasting for long periods of time.

I tried it while using my brakes sparingly and they worked fine. Although bout 3 miles down the road I started to lose brake pressure, the pedal became near impossible to push down, and then I lost my brakes all-together. I quickly started the car and they came back. Why did this happen? Did I do something wrong?

great troll- very sly! but i think there is a valid point here. do not sacrifice safety for gas ($) savings. I do find myself cringing at posts that advocate removing wipers and mirrors for millage gains. And turning your motor off can be a problem with vacuum assisted brakes. I personally will not do it.

[mikehallbackhoe]

you have power brakes. my 95 nissan pickup also has power brakes, and after a few pushes, I lose the vacuum but still have brakes, I just have to press harder. a little unnerving the first time, but now I don't think anything of it.

[GasSavers_JoeBob]

What the guy above me said. Your power brake booster will save enough vacuum for one or two stops before it is used up. Then the brake pedal will become very hard to push. Unless there is a problem, however, you should still be able to stop. No matter what kind of car you have. I had an '85 Lincoln Continental with anti-lock brakes (the first car to come with ABS standard, IIRC). The pump, a >$2000 part (I only paid $1000 for the whole car!) failed. This pump also acted as the power brake pump. I still drove the car, it just required me to pretend I was He-Man to push the pedal. Eventually I got a junkyard pump for $20 and fixed it.

If you don't feel safe using the brakes w/o power assist, go ahead and let the engine idle while you are coasting. Safety takes priority above all else, even gasoline savings!

[beb]

Does your car have ABS? (What car made this century doesn't?) If not, ignore this post. Even if you do have ABS, this post could still be nonsense.

Assuming that 'brakes locked' means 'brakes failed' (instead of unturning tires smoking and screching the car to a hard stop), annother possibility is that the ABS accumulator ran out of pressure. Unlike the absense of vacuum assit, when the accumulator has no pressure, the brakes barely function, if at all, no matter how hard you press; about the only way to reliably engage the brakes in this condition is with the emergency brake.

If the ignition had been left in 'run', this probably wouldn't have happened because the accumulator pump motor would have maintined pressure, but in 'aux' it will just bleed down after enough brake use.

A test of this would be to sit in a (unsloped) parking spot with the ignition in 'run' but with the engine not running (unstarted), and pump the brake pedal several dozen times. Every few pumps, you should hear the accumulator pump motor run (it's usually near the master cylinder, but I've seen it on the firewall near the transmission on a 96 Del Sol), and you should never lose brake functionality (even long after any vacuum has been consumed). If you can ID the sound of the accumulator pump motor occassionally running and the failure is replicated during this ignition in 'run' test, maybe it is vacuum assist causing it instead.

Then turn the ignition to 'aux' (or where ever you had it when the failure occured) and pump the brake pedal several dozen times - this time you shouldn't ever hear the accumulator pump and at some point the brakes should fail in the same way.

[theholycow]

As others have said, you run out of vacuum and will need to press the brake harder. As a 220 pound ex-bicyclist in a 3000 pound compact hatchback, I have enough leg power to do a decent job of operating a power braking system that has run out of power, but even then I avoid it. While I feel that the risk is small for me, it's still not acceptable compared to the savings.

Important: If you need to do that much braking, leave your engine ON! EOC (Engine-Off Coasting) is only for situations where you can coast a long time without needing to brake. Either you have not practiced coasting with the engine on, or you are trying to apply the strategy in an unsafe situation.

If you have a long downhill coast without other traffic and just need to keep slowing your car, you could practice pushing hard, or you could occasionally restart it to recharge the brakes. Another option might be to leave it in gear and running; google for "DFCO". Briefly, DFCO (Deceleration Fuel Cut Off) means that the computer shuts off all fuel to the engine while you are engine-braking.

Originally Posted by beb

Unlike the absense of vacuum assit, when the accumulator has no pressure, the brakes barely function, if at all, no matter how hard you press; about the only way to reliably engage the brakes in this condition is with the emergency brake.

This runs counter to my experience, common sense, common automotive engineering practices, and probably law. Even if the engine fails, it should always be possible to brake with the daily service brakes on 4 wheels instead of a possibly rusty disused parking brake which applies to two wheels (or on some models, apparently, just one).

[dutchdivco]

Regarding loosing the vacuum on power assist brakes; an easy answer is to tap into the vacuum line with a "tee", plumb in a 1-way valve, and a vaccuum resevoir. I have an old, (1965) industrial truck, (14,000 G.V.W.)where this was done at the factory. Reasoning was, if the engine dies, while going down a long downgrade while loaded, wouldn't have a run-away truck.The tank is about 10" in diameter, by 20" long. It held enough vavuum for 3-4 stops, and this was with 2 slave cylinders per wheel, front and rear, and drum brakes x 4.
I am unfamiliar with ABS brakes, but the previous posters post makes it sound like the accumulator pump runs on electricity, as he says you can hear it go on and off, with the engine off in a parking lot. Should be able to hook up a swith, so you can turn it on, while coastng. If it shouldn't run full time, could wire in a flasher unit, so it goes on and off? As I said, not familiar with ABS, so don't do this on my say so. However, regarding the vacuum resevoir, I KNOW they work! Jim

[palemelanesian]

I've seen this same post at CleanMPG and at ecomodder. Looks like a troll to me.