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Android Users - Coming Soon! - Migrating from aCar 4.8 to 5.0

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Old 07-02-2008, 04:30 PM   #11
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Quote:
Originally Posted by grey View Post
oh well, highly scientific research is hard to dispute...
ask a person who knows, such as a reputable transmission mechanic.
What causes the failure? How does it fail?
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Old 07-02-2008, 09:44 PM   #12
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Originally Posted by theholycow View Post
What causes the failure? How does it fail?
as with most transmission failures, HEAT

To be fair I did a search to see why this bit of information is not widely known. This took 14 seconds to find:

action.publicbroadcasting.net/cartalk/posts/list/669010.page
In short, don't do it.

The tranny hydraulic pump is driven by the input shaft from the torque convertor. Therefore if the output shaft is spinning at 50mph and the engine is idling it won't be delivering the required pressure to the tranny. It's the same as running your engine at 3000rpm with an oil pump delivering 1000rpm of oil pressure. The result is increased wear, burnt tranny fluid and a premature visit to the tranny shop.

Plus it's dangerous, vehicle dynamics are balanced around an on load system, when you unload that system - coasting in neutral, the vehicle is inherently unstable. Try a sharp turn in neutral sometime and you'll get the idea.
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Advice to readers of this board:
If you have an Automatic Transmission, then do not coast in Neutral.
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Old 07-03-2008, 05:44 AM   #13
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i will say this. when i coasted in D for example getting up to 60mph and then coasting until 50-55mph i got 37.5 mpg. thinking that coasting in N since i could go futher, doing the same speed my mpg went down to 36 down more to 33. but with a scangauge or the like to see whats going on. i'm going to have to stay with coasting in D since i know that works. you all can see my gaslog and see it go down
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Old 07-03-2008, 07:49 AM   #14
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Quote:
Originally Posted by grey View Post
To be fair I did a search to see why this bit of information is not widely known. This took 14 seconds to find:

action.publicbroadcasting.net/cartalk/posts/list/669010.page
So? It's just another forum. I can find loads of forum replies saying it's okay in the same 14 seconds, probably using exactly the same search terms.

Quote:
The tranny hydraulic pump is driven by the input shaft from the torque convertor. Therefore if the output shaft is spinning at 50mph and the engine is idling it won't be delivering the required pressure to the tranny.
My automatic has an idiot light that's known to come on in stages as the transmission gets warm. It comes on long before temperatures cause long-term damage, let alone immediate damage. It has never come on during neutral coasting, even at highway speeds on long down slopes.

Anyway, in D with the torque converter unlocked and your foot off the gas, the engine speed goes WAY down. Depending on your road speed, engine may get very close to idle.

Some people with automatics report that their engine does not go completely down to idle when in N. Perhaps their computer is keeping the speed up to keep the tranny cool, that was one proposed explanation (another being fluid resistance in the tranny transmitting small amounts of power).

Can someone with a tranny temp gauge or ScanGauge give us the straight dope on this? Does your tranny temp go up while neutral coasting, and if so, how much? My ELM327 ought to show up soon, so I'll be able to log some data too.

Quote:
Plus it's dangerous, vehicle dynamics are balanced around an on load system, when you unload that system - coasting in neutral, the vehicle is inherently unstable. Try a sharp turn in neutral sometime and you'll get the idea.
Blah blah blah, same old FUD there. I do dozens of sharp turns in neutral every day with my tires complaining so I don't have to waste any energy by braking before a turn. Handling is the same as being off the gas pedal in an automatic (don't forget that at the speeds we're talking about, the torque converter lets the engine down to ALMOST idle). If you're going so fast around the turn that not having the drive wheels* drag slightly is going to upset stability, you are going WAY too fast.

*: BTW, is your idea for front or rear wheel drive? Having the front wheels drag slightly from engine braking will upset the car differently from having the rear wheels do so...and then there's weight distribution, pavement changes, general differences in the car and the driver...

If you're not confident in your safety while coasting in neutral, then you definitely should not do it. Most people who do neutral coasting are fine, we manage to survive without being able to accelerate away from a deer crossing the road or whatever, and do not have handling problems.
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Old 07-03-2008, 08:37 AM   #15
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Quote:
Originally Posted by theholycow View Post
So? It's just another forum. I can find loads of forum replies saying it's okay in the same 14 seconds, probably using exactly the same search terms.



My automatic has an idiot light that's known to come on in stages as the transmission gets warm. It comes on long before temperatures cause long-term damage, let alone immediate damage. It has never come on during neutral coasting, even at highway speeds on long down slopes.

Anyway, in D with the torque converter unlocked and your foot off the gas, the engine speed goes WAY down. Depending on your road speed, engine may get very close to idle.

Some people with automatics report that their engine does not go completely down to idle when in N. Perhaps their computer is keeping the speed up to keep the tranny cool, that was one proposed explanation (another being fluid resistance in the tranny transmitting small amounts of power).

Can someone with a tranny temp gauge or ScanGauge give us the straight dope on this? Does your tranny temp go up while neutral coasting, and if so, how much? My ELM327 ought to show up soon, so I'll be able to log some data too.



Blah blah blah, same old FUD there. I do dozens of sharp turns in neutral every day with my tires complaining so I don't have to waste any energy by braking before a turn. Handling is the same as being off the gas pedal in an automatic (don't forget that at the speeds we're talking about, the torque converter lets the engine down to ALMOST idle). If you're going so fast around the turn that not having the drive wheels* drag slightly is going to upset stability, you are going WAY too fast.

*: BTW, is your idea for front or rear wheel drive? Having the front wheels drag slightly from engine braking will upset the car differently from having the rear wheels do so...and then there's weight distribution, pavement changes, general differences in the car and the driver...

If you're not confident in your safety while coasting in neutral, then you definitely should not do it. Most people who do neutral coasting are fine, we manage to survive without being able to accelerate away from a deer crossing the road or whatever, and do not have handling problems.
On the Beast it takes about half a second total for me to extend my right hand from the wheel, shift to D, and wait for the tranny to engauge before hitting the accelerator. If you don't have this 1/2 second you're probably going to hit the deer anyway.
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Old 07-03-2008, 08:49 AM   #16
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Quote:
Originally Posted by grey View Post
as with most transmission failures, HEAT

To be fair I did a search to see why this bit of information is not widely known. This took 14 seconds to find:

action.publicbroadcasting.net/cartalk/posts/list/669010.page
In short, don't do it.

The tranny hydraulic pump is driven by the input shaft from the torque convertor. Therefore if the output shaft is spinning at 50mph and the engine is idling it won't be delivering the required pressure to the tranny. It's the same as running your engine at 3000rpm with an oil pump delivering 1000rpm of oil pressure. The result is increased wear, burnt tranny fluid and a premature visit to the tranny shop.
Ummmm my transmission pump is driven by the OUTPUT shaft.
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Old 07-03-2008, 09:37 AM   #17
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Originally Posted by RoadWarrior View Post
Ummmm my transmission pump is driven by the OUTPUT shaft.
AFAIK, that's not a common design, most automatics are pumped by the input shaft. That makes EOC bad for them but engine-on neutral coasting seems to be fine.
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Old 07-03-2008, 09:52 AM   #18
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Quote:
Originally Posted by grey View Post
The tranny hydraulic pump is driven by the input shaft from the torque convertor. Therefore if the output shaft is spinning at 50mph and the engine is idling it won't be delivering the required pressure to the tranny.
But there is no load on the transmission, so what difference does it make?


Quote:
Plus it's dangerous, vehicle dynamics are balanced around an on load system, when you unload that system - coasting in neutral, the vehicle is inherently unstable. Try a sharp turn in neutral sometime and you'll get the idea.
Hahahaha. OK. So did you ever go around a turn driving a stick? You drive around turns by mashing the gas pedal? I doubt it.

The 'vehicle is inherently unstable?' Really? I wonder how I didn't notice that while P&Ging and driving around turns in "N." I mean, of the car is 'inherently unstable' it would take an awful lot of work to keep it on the road, right? You don't think I'd notice that? I'm surprised I didn't fling my Camry right off the road with all that unstable-ness.
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Old 07-03-2008, 11:13 AM   #19
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Every auto I have seen the primary pump is driven by flanges off the torque converter, it works whenever the engine is running.

Without the primary pump you are in trouble.

I know it would wreck the early Z trannies to tow them.

regards
gary
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Old 07-03-2008, 01:44 PM   #20
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Quote:
Originally Posted by theholycow View Post
AFAIK, that's not a common design, most automatics are pumped by the input shaft. That makes EOC bad for them but engine-on neutral coasting seems to be fine.
How do you find out about that? I looked in my manual and it says that I can tow my car with the front wheels so does that mean I'm safe to EOC?
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