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Old 07-20-2007, 12:39 PM   #1
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Q&A on Power Brakes

I'm driving a '99 Toyota Camry LE 4 cylinder automatic. I recently started engine off coasting (EOC) and have noticed a couple of times that my brakes suddenly get very hard.

Most times braking during EOC is pretty normal. When it happens, it seems like the brakes are quitting on me. I've started the engine back up, braked normally, and continued on.

Not being mechanically inclined, I figure it's probably still got brakes, just unassisted. I intend on proving this to myself at a more convenient and safe time.

Could anyone please give me some reasoning behind the event for my own reference. Thanks in advance.
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Old 07-20-2007, 12:57 PM   #2
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The brakes are assisted by vacuum from the engine. Usually there is a vacuum reservoir that will allow a couple of assisted stops with the engine off. Then, once the vacuum is gone ("used up"), it gets REEEEAAAALLLLY hard to stop. At least when I have tried it...
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Old 07-20-2007, 01:10 PM   #3
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Hard is right. Feels like a big ol' rock!

So far, EOC with an auto tranny seems to be okay. Nothing funky going on that I can detect. I'm going to read my manual to see what it says. If there was an issue, what would the indications be like?
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Old 07-20-2007, 01:11 PM   #4
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The power assist for brakes comes from a turning engine creating vacuum. When you have the engine shut off and in neutral, there is no vacuum produced. 2-3 brake applications and the vacuum stored is used up.

Starting the engine immediately replenishes the vacuum for the brakes.

You are only losing power assist, not your brakes. It just requires hard pressure on the pedal. An auxillary vacuum tank and/or an electric vacuum pump would help alleviate this.
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Old 07-20-2007, 01:17 PM   #5
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I'm definitely outclassed! That's why I like this site.

So, when I feel that rock again and conditions are within reason, push hard and see what happens. It's been a very long time since I've driven anything without power brakes.
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Old 07-20-2007, 01:39 PM   #6
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I experience that at one location on a vending route that has a good "potential energy" parking spot. I park nose-downhill and when leaving, I roll out of the parking lot and maybe ten additional feet to a stop sign without starting the engine.

The 15 minutes to a half hour I spend at the location is enough time for vacuum to bleed off. I have no problems stopping but I'm moving at a relatively slow rate, there may still be a little vacuum helping me, and I have to push hard on that brake pedal! I would definitely suggest that you get a solid feel for this before relying on unassisted braking in "real world" conditions... but yes, you should be able to stop.

I'd also suggest you not EOC an automatic until you've research what damage you might be doing to your vehicle. Automatic transmissions are not cheap. Check your manual to see what it says about towing as a first step. Then see what you can find out about throwing your transmission in and out of neutral while rolling along at a good clip. All of it may be perfectly okay for your car, but the peace of mind of knowing that what you're doing is safe is worth a lot.

A third thing to consider is legality in your area; be sure you're well-informed as to what the laws are so you can make an informed decision.

Good luck with your efforts. Keep us posted!

Rick
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Old 07-20-2007, 01:46 PM   #7
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I just pulled out the manual. It says not to tow automatic transmissions with the front wheels on the ground. That would mean the front wheels would be rolling in reverse. For a manual transmission, it says to switch the ignition key to ACC after placing in Neutral.

Sometimes good advice is hard to listen to. I kind of like EOC, but I also need to exercise caution and patience. Knowledge is a valuable thing.
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Old 07-20-2007, 02:00 PM   #8
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Quote:
Originally Posted by BearDog1957 View Post
I just pulled out the manual. It says not to tow automatic transmissions with the front wheels on the ground. That would mean the front wheels would be rolling in reverse. For a manual transmission, it says to switch the ignition key to ACC after placing in Neutral.

Sometimes good advice is hard to listen to. I kind of like EOC, but I also need to exercise caution and patience. Knowledge is a valuable thing.
Ask omgwtfbyobbq http://www.gassavers.org/member.php?u=415

He has a Camry and you can believe what he tells you.
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Old 07-23-2007, 07:34 AM   #9
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Quote:
Originally Posted by BearDog1957 View Post

So far, EOC with an auto tranny seems to be okay. Nothing funky going on that I can detect. I'm going to read my manual to see what it says. If there was an issue, what would the indications be like?

In my experience, an auto tranny failing can show all sorts of symptoms. The classics are things like hard shifting between gears, hard shifts into drive/reverse, grinding/howling (more obvious at slower speeds....at this point, you may not be able to get to the high speeds).....burned/dark tranny fluid, slipping while in gear (seems like it goes into neutral when you haven't touched the shifter), missing gears while driving, etc....

Folks have told me that EOC with an auto tranny is just fine. Personally, I know the transmission in my Jeep is roughly a $1200-1800 job, for repair/replacement. I know I won't save that much in gas, so I'm not taking the risks.

P.S. By the time you get to most of the symptoms I've listed above, you may already be in trouble. Check your fluid, make sure that it's not dark in color, or smelling burned. If it is, change it. I wouldn't recommend power-flushing the transmission unless you know the history of the car (specifically, how often the transmission was serviced). Sometimes they don't like that. If you're getting hard shifts and the like already, try using something like a Lucas Auto Tranny Fix (http://www.lucasoil.com/products/dis...tid=2&loc=show)
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Old 07-23-2007, 04:29 PM   #10
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On the brakes, just like everybody says, it's the leftover vacuum used to assist the braking running out. I'm pretty used to manual brakes by now, I learned stick in a '66 Mustang with unassisted, manual brakes (also had manual steering, which was an adventure in and of itself, and a clutch that Arnold Schwarzeneggar would be proud of). It was an adventure at first, but I hardly notice it now when brake/steering assist runs out...
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