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Old 11-28-2006, 12:52 PM   #21
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cfg83 : I am assuming the car is a manual. Double-declutching is just a way of reducing the stress on the synchromesh when changing gear.

Normally, if you are coasting, then input shaft will be spinning the speed of the engine (700RPM), whereas the output shaft will be spinning at a different speed.

When you go to put the car in gear (with the clutch down), the two shafts must be spinning at exactly the right speed, or the gear cogs will crunch badly. Synchromesh makes the input shaft spin at the correct speed as the output shaft, so that they can engage properly. If the synchro is worn, then the gears crunch (even with the clutch pressed down).

When changing from 1st-2nd, 2nd-3rd, 3rd-4th, 4th-5th, you can quickly change gear (synchro will help you, gearstick will have some resistance to
going in gear), or gently do it (gently resistance, when speeds match, gear will go in).

If changing down from 4th - 3rd... Or, from neutral - 5th, the synchromesh has to do a lot of work. Double-declutching can reduce the amount of work it has to do.

examples of double-declutching

(1) Car is in neutral, coasting along at 40mph
(2) If 5th gear would be 1500RPM, then rev engine to 1700RPM, *then*
press clutch in, change gear, and it will change a lot more easily.

(1) Car is in 5th, and you want to change to 4th
(2) Press clutch down, put it in Neutral
(3) Rev engine to a little bit above the RPM you would want to be in 4th
(4) Press clutch down, and change gear.

Double-declutching can also be useful for cars with worn synchromesh, particularly on 1st gear (like mine)

SVOBoy : I do engine-on coasting, but, the motorways here tend to
have lots of rolling hills, and the lorries are speed limited to 56MPH by
law - gives lots of opportunity for getting good fuel economy!
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Old 11-28-2006, 01:19 PM   #22
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Quote:
Originally Posted by psyshack
Metro

I do this alot! I look at it as load and bleed. It is a basic standard tool for me. I use the lay of the land to make it happen. There always has to be I very slight up hill for the load or say pulse if you will. and then a slight bleed on the ever so slightly downhill. I never see so called flat ground to work with,,, Thank GOD!!!
Well put. Pulse and glide no. Pluse and bleed yes. I also do this quite a bit using the terrain as your friend. No conclusive data except that the 90 day MPG figure kept going up once I got it down.
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Old 11-28-2006, 06:43 PM   #23
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lol, what kind of car makes the EEEEEEoooo noise?

Also, isn't pulse and bleed exactly what we are tryign to avoid when we use cruise control? I thought that it's more efficient since we're not constantly speeding up and slowing down?
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Old 11-28-2006, 07:10 PM   #24
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hahaaha i thought you were talking about bleeding the brake lines. or maybe the clutch line.
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Old 11-28-2006, 09:49 PM   #25
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I've tried 'pulse and bleed' with the piece of **** Suzuki I drive. Didn't work well in my case. Better kept at a constant speed.

Quote:
There's the Harley riders who feel so inadequate and starved for attention they do everything in their power to maximize their noise output, all in a juvenile effort to get noticed: "PLATPLATPLATPLATPLATPLATPLATPLATPLATPLATPLATPLATP LAT."
While of no intention of my own, that is pretty much what the Triumph sounded like. Only louder and even more obnoxious. Then when you step on the gas...
"R-I-I-I-I-I-I-I-I-I-NNNNNNNN". Like a Harley getting *** raped by a Formula race car... Had no problem setting off alarms on parked cars.
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Old 11-28-2006, 09:58 PM   #26
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omgz, i hated that my beater diesel sounded like rice. but a glasspack was $20 while a new exhaust would've been at least $100, and running around with an unmuffled diesel is just crazy. sounded like a tug boat or something, i could idle through a parking garage and set off alarms.
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Old 11-28-2006, 11:47 PM   #27
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landspeed -

Quote:
Originally Posted by landspeed
cfg83 : I am assuming the car is a manual.
Yes, a manual.

Quote:
Double-declutching is just a way of reducing the stress on the synchromesh when changing gear.

Normally, if you are coasting, then input shaft will be spinning the speed of the engine (700RPM), whereas the output shaft will be spinning at a different speed.

When you go to put the car in gear (with the clutch down), the two shafts must be spinning at exactly the right speed, or the gear cogs will crunch badly. Synchromesh makes the input shaft spin at the correct speed as the output shaft, so that they can engage properly. If the synchro is worn, then the gears crunch (even with the clutch pressed down).

When changing from 1st-2nd, 2nd-3rd, 3rd-4th, 4th-5th, you can quickly change gear (synchro will help you, gearstick will have some resistance to
going in gear), or gently do it (gently resistance, when speeds match, gear will go in).

If changing down from 4th - 3rd... Or, from neutral - 5th, the synchromesh has to do a lot of work. Double-declutching can reduce the amount of work it has to do.

examples of double-declutching

(1) Car is in neutral, coasting along at 40mph
(2) If 5th gear would be 1500RPM, then rev engine to 1700RPM, *then*
press clutch in, change gear, and it will change a lot more easily.
....
Ok, I *almost* do something like this already, because I hit the accelerator right before I press the clutch to go from Neutral to 5th, but I am not consciously trying to match RPMS, it's just a smoother way to engage the gear. I am lucky in the sense that with my car, in 5th gear, the MPH and RPM needles "line up" at the same angle, so it is easy to "match the needles" to engage 5th.

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Old 12-01-2006, 01:20 PM   #28
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Quote:
Originally Posted by The Toecutter
I've tried 'pulse and bleed' with the piece of **** Suzuki I drive. Didn't work well in my case. Better kept at a constant speed.



While of no intention of my own, that is pretty much what the Triumph sounded like. Only louder and even more obnoxious. Then when you step on the gas...
"R-I-I-I-I-I-I-I-I-I-NNNNNNNN". Like a Harley getting *** raped by a Formula race car... Had no problem setting off alarms on parked cars.
I never thought reading a series of posts would be so loud! My eyes are ringing!!! ROFLMAO !!!
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Old 12-01-2006, 04:00 PM   #29
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And lets not forget the rice burners honnnNNNNNNNNnnddaaaa yaaaAAAAAAAAMMMMMMMMAAAAAAhhhhaaaaaaaaaaa and KaaaaaAAAAAAWAsssssaaaaakkkkkkkkkiiiiiiii
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