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Old 11-21-2008, 04:07 PM   #1 (permalink)
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Manual Cars and Popping the Clutch (to re-start engine)

Over the summer I recently got a new car, the current one I driver, and it was manual rather than automatic. I found that you can turn the car off and coast saving mass amounts of gas, not an entirely novel concept I know. But I am not totally aware as to what the possible negative effects of constantly turning off a car can be. I know the the starter can go bad eventually, not a cost I want to incur, so I found out about the idea of popping the clutch, which I have found can be done in any gear. Generally I turn the car off at around 50, coast to a desired speed, then pop the clutch in the conditionally required gear. I know little to nothing about the interworkings of a car, so might someone shed some light onto what problems this could cause if any?

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Old 11-21-2008, 04:48 PM   #2 (permalink)
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It'll increase clutch wear a little (depending on how smooth you are). Thats really about it. If you do it wrong you can damage your engine of course (bump start in 1st = boom).

See: http://ecomodder.com/forum/showthrea...gine-1141.html
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Old 11-21-2008, 06:01 PM   #3 (permalink)
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I don't remember who here said it first (not me, can't claim credit), but a good rule of thumb when bump-starting is use the gear that's two higher than what you'd normally use for that speed. E.g., in my bucket, if I need to bump-start at 25mph, that's normally 3rd gear, so bump the car in 5th, depress the clutch, and select 3rd to continue driving.

Another consideration: The faster you're going, the less aggressive you can be with engaging the clutch to spin the engine. If I'm trying to bump the engine at 20 mph, I'll put it in 4th and let the clutch out pretty briskly and pretty far, to make sure it engages firmly to spin the motor. But at 50 mph in 5th, I can just "feather" the clutch out a few inches into its travel, very quickly, and the engine catches.
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Old 11-21-2008, 06:39 PM   #4 (permalink)
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I agree with Joe. Using the method he describes is the way I perform "The Bump". As far as increased wear, it is negligible, as you are only *just* touching the plate to the flywheel to give it a turn. In fact, one could argue that you are saving wear on the plate and flywheel, depending on whether you would have shifted during the coast or not, as with "normal" driving.
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Old 11-21-2008, 06:54 PM   #5 (permalink)
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Quote:
Originally Posted by Daox View Post
[...]1st = boom).
Just like that...

I always bump start in 5th around 20 mph, that makes it really easy and completely transparent to passengers.
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Old 11-21-2008, 07:11 PM   #6 (permalink)
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If your the guy that is going to be doing the clutch replacement, then I don't think you could ever argue that there is not going to be clutch wear from popping the clutch. You save $0.01 but incur the cost of replacing the clutch sooner? Any time sooner is to soon.
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Old 11-21-2008, 11:50 PM   #7 (permalink)
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Quote:
Originally Posted by Whoops View Post
If your the guy that is going to be doing the clutch replacement, then I don't think you could ever argue that there is not going to be clutch wear from popping the clutch. You save $0.01 but incur the cost of replacing the clutch sooner? Any time sooner is to soon.
The thing we forget here is that the mean time between failure on manual transmissions vs automatics is so far in favor of the manual that it is not even funny. I replaced my clutch in my current ride at 96,000 miles, and did the replacement myself with the help of a friend and $400. It wore out that soon because I learned how to drive stick on that car, and so did my then girlfriend, now fiance. The clutch, no matter how many bump starts I perform on it, will never incur the abuse that it did when two people learned how to drive on it. Enough said.
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Old 11-22-2008, 09:05 AM   #8 (permalink)
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I think it's important to say that "popping" the clutch isn't what people are doing. It's much more subtle than that.

Maybe you're only using the common expression and not the technique itself, but "Popping" the clutch will impart more shock to the engine/drivetrain components and is probably uncomfortable for the passengers.

Even "bump" starting is a misnomer. As Tasdrouille pointed out, done well, restarting the engine with the clutch should ideally be imperceptible to anyone riding with you.

See http://ecomodder.com/forum/showthrea...gine-1141.html

PS - Tas - amazing video. The grip of those front tires must be phenomenal!
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Old 11-22-2008, 09:47 AM   #9 (permalink)
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Quote:
Originally Posted by Whoops View Post
If your the guy that is going to be doing the clutch replacement, then I don't think you could ever argue that there is not going to be clutch wear from popping the clutch. You save $0.01 but incur the cost of replacing the clutch sooner? Any time sooner is to soon.
Your clutch gets worn by driving it, far more so in accelerating the whole car than in bringing an engine up to idle speed. much more mass and slippage there.

And your $0.01 is more like thousands of gallons. You are comparing the lifespan of a clutch to the gas saved on a single short coast maybe?

The clutch cost me ~$50 and a day, like once every 10 years. Compared to thousands of gallons saved over the same timeframe, it's a no brainer for me.
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Old 11-22-2008, 06:50 PM   #10 (permalink)
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Quote:
Originally Posted by MetroMPG View Post
The grip of those front tires must be phenomenal!
static friction, Fs = Fn * us (weight of car * coefficient of static friction) Dry, warm tires on asphalt basically all have a coefficient of static friction of .95 to 1.0. When the car rocks forward due to the slowing of the car, the weight all sits on the front tires, so the frictional force becomes essentially equal to the weight of the car, which is a lot!
One of my friends did this in an old beretta; he'd shift to R from like 3 mph forward and hit the gas to do a reverse wheelie. luckily it didn't break the ol' car.
Pretty sweet video - would be scary as the driver! I've seen similar videos where a RWD car breaks its driveshaft and it catches the ground, sending the rear end flying.

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