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Corolla 07 Coasting on Neutral?

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Old 07-18-2008, 12:20 PM
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MaxxMPG MaxxMPG is offline
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Re: Corolla 07 Coasting on Neutral?

Quote:
Originally Posted by DocOc View Post
just to add my 2 cents. i shift from D to N to D alot on downhills or when the road is empty enough to coast. i drive an auto tranny that is not flat towable. there is absolutely no 'bump' going from N to D at speed (80km/h and under), however there is a significant bump going from idle N to idle D (when starting the car at a red light for instance).
if anyone can enlighten me as to why this happens, i would greatly appreciate it
DocOc, see the posts above that describe the function of the overrunning (one way) clutches in the transmission. When shifting from N to D at speed, the output side is running faster than the input side, so the sprag freewheels. When stopped and shifting to D, the input is running much faster than the stopped output side, so the sprag transmits torque. You will feel that "bump" any time you shift from N to D where the input speed is greater than the output speed inside the transaxle. A poorly executed "rev match", for example, involving a shift to D with the engine speed at 2000rpm will cause quite a bump. If you rev to 7000 and shift to drive (as mentioned in an earlier post), the input sprag is often a common failure point. Once it shatters, the car doesn't move in either direction.

Below is an exploded view of the 4T45E Hydramatic transaxle. Each design is different, but the theory remains the same. I outlined the input sprag and direct and forward clutches. When shifting this transaxle to N, the direct and forward clutches release. If in top gear when shifted to N, the intermediate band also releases. The input sprag is closer to the engine than these clutches and bands. When shifting back to D, the forward clutch and direct clutch apply and transmit torque from the drive wheels, spinning the intermediate shaft up to a speed higher than the input shaft behind the torque converter. The input sprag (one way clutch, like a ratchet-wrench) allows this speed differential without any wear or shudder.

Hope this helps!

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Old 07-18-2008, 12:25 PM
AirGibson AirGibson is offline
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Re: Corolla 07 Coasting on Neutral?

Maxx, that is some excellent info. If it holds that N-> D transitions cause no extra stress on the tranny (even without rev-matching), then I will have to consider P&G (without FAS) in my automatic.

Admittedly, any common technician I've asked about this tells me otherwise. They probably don't know much about this specific situation or transmissions in general, but it is a very common perception that going from N-> D while at speed is "bad" in an automatic, especially if not rev-matched. Are there any technical references I could refer them to that confirm much of what you've discussed?

IMO, that is a very significant misconception that we'd want to get cleared up. I would think a stickied article on the subject would be worthwhile: "Why shifting in and out of Neutral in an automatic will NOT cause extra transmission wear in most modern vehicles"



Edit: Ahhh, just read the above. So the engine "input" running slower than the axel is okay thanks to the sprag, but the reverse is not true. That is making sense.

Last edited by AirGibson : 07-18-2008 at 12:30 PM.
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Old 07-18-2008, 01:31 PM
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Re: Corolla 07 Coasting on Neutral?

Quote:
Originally Posted by AirGibson View Post
Admittedly, any common technician I've asked about this tells me otherwise. They probably don't know much about this specific situation or transmissions in general, but it is a very common perception that going from N-> D while at speed is "bad" in an automatic, especially if not rev-matched. Are there any technical references I could refer them to that confirm much of what you've discussed?
A couple of thoughts:
Most "common technicians" are not well versed in transmission design and will only guess at how N->D shifting at speed will affect transmission life. And that is understandable considering the wide range of different designs. If you go to an auto-repair shop with a transmission problem, anything they can't fix from "outside the box" will be repaired with a rebuilt unit they will get from an outside source. They are not familiar with the internals and how various shifting and other operator inputs will affect it. So they invariably issue a blanket "that's bad to do" disclaimer rather than take a guess.

Tranny-shop technicians are a safer bet for information, but they are not likely to offer up too much information to unknown people. Their junior mechanics are just involved in swapping out units rebuilt by an outside source and they have no idea what's going on inside the case. Senior mechanics don't want the liability of hearing you say, "You said I could do this and my transaxle blew up!" So they will likely also give you a generic "no".

The technical reference they would want to review would be the service manual for the particular transmission in question. In the first chapter, they typically describe the function of the unit, complete with acceptable line pressure readings, band accumulator spring rates, and clutch tolerances. By analyzing exactly how the transmission creates each gear via the clever application of friction clutches and/or bands, they can determine whether an N-to-D shift would cause any undue stress on any of the components.

Quote:
Originally Posted by AirGibson View Post
IMO, that is a very significant misconception that we'd want to get cleared up. I would think a stickied article on the subject would be worthwhile: "Why shifting in and out of Neutral in an automatic will NOT cause extra transmission wear in most modern vehicles"
The keyword above - "*most* modern vehicles". Wayne had an awful time getting a rented Lincoln Aviator back into Drive after a FAS a few years ago. So anyone with the same transmission (4R55*, 5R55*, which I collectively and derisively call PintoGlide because they are based on the old C3 Pinto transmission from the 1970s) may well experience the same problem. As I noted before, it appears to be a computer-related issue and not the result of undue stress on the mechanical parts.

As with so many other questions raised in these forums, we sometimes need to just rely on our own past experiences and those of our trusted members. For many of our questions, there is no reliable source of hard data we can depend on. But what we do have here in the forums is a wealth of knowledge and experience, and sometimes heated debates. And we can all see that there are plenty of debates raging on these forums -
- "My tire pressure is over max-sidewall and I can stop while driving down the side of a glacier" vs "Going over max reduces traction and will cause a spinout on dry pavement".
- "Never FAS in an automatic car that is not flat-towable" vs "My car isn't and I never had a problem".
...and so on.
Every post that is based on driver/vehicle experience is to be taken into consideration. Even if it only represents a one-in-a-million instance, the information still is there for your review.

With that in mind, any sticky should probably be a listing of vehicles that have lots of miles and lots of years of use that have been coasted in N - engine on or off - along with any relevant notes the driver wants to add. Over time, patterns will develop and readers can see how many different samples of the same vehicle handled FAS or NICE-on just fine without any issues.

CleanMPG members have saved close to 200,000 gallons of fuel, and counting! This represents a LOT of miles, and therefore a LOT of experience gained by members who drive automatics. If enough of these members say "no problem" or "don't do this" regarding a question I have, I will go with their general consensus.
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Old 07-18-2008, 03:25 PM
AirGibson AirGibson is offline
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Re: Corolla 07 Coasting on Neutral?

Quote:
Originally Posted by MaxxMPG View Post
As with so many other questions raised in these forums, we sometimes need to just rely on our own past experiences and those of our trusted members. For many of our questions, there is no reliable source of hard data we can depend on. But what we do have here in the forums is a wealth of knowledge and experience, and sometimes heated debates.

...

CleanMPG members have saved close to 200,000 gallons of fuel, and counting! This represents a LOT of miles, and therefore a LOT of experience gained by members who drive automatics. If enough of these members say "no problem" or "don't do this" regarding a question I have, I will go with their general consensus.
True that. I think part of the problem is that the "collective experience" is pretty largely skewed against shifting N -> D while in motion in a modern automatic. If they're wrong, that is a pretty significant misconception that could save a lot of people a lot of mileage if they knew better

I've been searching decently hard for this kind of info and it isn't easily found. Keep up the good work. I appreciate the education.
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Old 07-18-2008, 04:26 PM
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Re: Corolla 07 Coasting on Neutral?

Quote:
Originally Posted by AirGibson View Post
I've been searching decently hard for this kind of info and it isn't easily found. Keep up the good work. I appreciate the education.
You're right. I just went to google and searched for ["coasting in neutral" transmission] and I was shocked at the misinformation. Many of the threads dismiss the question and say it is illegal. Many assume it's a reference to NICE-off and speak of failures from lack of lubrication. Many say you will damage your brakes. And many say yes, it will damage your transmission, although they say that either "somebody told them this", or they otherwise are just coming to this conclusion without any knowledge of how their transmission works. All appear to be based on speculation and misguided logic.

There is no substitute for owners manuals, factory manuals and other sources of information from the manufacturer. If shifting between N and D caused any problem with reliability or driveability, they would either change the transmission controller to refuse to re-engage Drive, or they would include a scary warning message in the owners manual. They did exactly that in the CVT-equipped Saturns.

Almost 50 years ago, GM rolled out the infamous Roto-Hydramatic transmission. It was notoriously unreliable and quirky. Even today, several generations later, this "Slim Jim transmission" is still hurting the resale value of classic Pontiacs and Oldsmobiles that used it. One of the most common problem spots was the internal fluid coupling, which was a sort of hybrid between a fluid coupling and a true torque converter. Most of the failures were from overheating since the coupling was deep inside the transmission rather than being bolted to the front of it. On paper, it was a great idea. But in the real world, some people would press the gas a bit to hold the car on a steep uphill or find other ways to stall the converter. The heat would cause the failure. It's been said that this is the transmission that put AAMCO on the map. The result - Later cars had a sticker under the hood and a paragraph in the owners manual warning that drivers and technicians must never press the accelerator while the car is in gear if vehicle motion is prevented. It took them a few years to figure out what was causing the problem, but the basic design was flawed and there was no simple fix for it. The 1964 factory service manual, page 6-3 has the stern warning - "Under NO condition should the transmission be stall tested as the excessive heat developed will damage the unit."

In today's America, where we have 6.28 lawyers for every citizen, and network news "Consumer Watchdogs" who are waiting in the wings with mini-DV cams, the automakers are not going to build anything that can be driven in a way that will cause it to self-destruct. Anything drivers can dream up to cause this mechanical meltdown will be addressed in the owners manual or via several obnoxious warning stickers liberally applied throughout the vehicle.

On page 2-28 of my car's owner's manual, it says, "NEUTRAL (N): In this position, your engine does not connect with the wheels. To restart when you are already moving, use NEUTRAL (N) only. Also, use NEUTRAL (N) when your vehicle is being towed." (bold emphasis added). This states "already moving", shifting to N to restart, and then... They don't say, but shifting to Drive would be the logical next step. If not, they would say, "Stop the vehicle, restart, shift to drive, and take off". Will repeated N-D shifts cause wear long-term? If it did, I'm sure they would find a spot among the 438 pages to add the paragraph, "Do not do this frequently, or you could damage your transaxle. This damage would not be covered by your warranty. You or your passengers could be injured or killed by being crushed under the weight of transaxle repair invoices." etc etc.
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Old 07-18-2008, 06:47 PM
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Re: Corolla 07 Coasting on Neutral?

This is the best treatment I have seen of NICE-ON for automatics. I nominate for sticky or conversion to an article.

Many thanks to MaxxMPG, AirGibson, and all other contributors.

In order of preference for FE in a non-CVT automatic transmission vehicle (and only where traffic, etc conditions permit):
1) FAS, but only if flat-towable and not prohibited by warnings or experience
2) NICE-ON (idling stinks, but glides pay off in the end)
3) Engine braking with DFCO (too much speed for NICE-ON, need to slow quicker)
4) Engine braking without DFCO (low RPM or cold engine, etc)
5) Friction brakes

(Same list applies to manual trannys, but FAS is more likely to be allowed for them)

DFCO is great down a mountain or when traffic keeps you at speed too long. Or a light changes on you, etc. My Taco will only DFCO when warm with RPM above 1350 or so, and requires the moon in a certain phase I think. The CRV DFCO's more readily, and the FIT requires an act of Congress to allow fuel to the cylinders. Love the Fit. I use its paddle shifters to DFCO all the way to a crawl. Don't use the up paddle much.

But DFCO isn't gliding, its braking. Motto from bicycling: Brakes just slow you down.

For FE, there is nothing like a FAS or NICE-on. Wish all my auto's were manual, but I didn't know any better until the Fit purchase, and did not make the call on that choice.

The Taco will give the rated 17 city, 20 highway if you air up the tires put it in gear and drive reasonably. But with nice-on I get 20-24 in town and on slow highways. Doesn't sound like much, but it is a 20 to 40% improvement. I don't P&G on the freeways, just try to limit speed and DWL. At about 23 mpg, this is a 15% improvement. Just too much traffic and wind resistance at freeway speed for P&G/NICE-on to be worth it to me.

Sorry for the ramble.
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Old 07-18-2008, 07:40 PM
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Re: Corolla 07 Coasting on Neutral?

This is very interesting; I'll have to try a non-rev shift at higher speeds and see if there's a bump. I too get a bump at lower speeds or from a complete stop.

How does one get DFCO with engine braking?

In my car it's:

P
R
N
D
4
3
2
L

From the manual:

(c) Using engine braking

To use engine braking, you can downshift the transmission as follows:

- Shift into the "4" position. The transmission will downshift to fourth gear and engine braking will be enabled.

- Shift into the "3" position. The transmission will downshift to third gear when the vehicle speed drops down to or lower than 141 km/h (76 mph), and stronger engine braking will be enabled.

- Shift into the "2" position. The transmission will downshift to second gear when the vehicle speed drops down to or lower than 89 km/h (48 mph), stronger engine braking will be enabled.

- Shift into the "L" position. The transmission will downshift to first fear when the vehicle speed drops to or lower than 40 km/h (21 mph), and maximum engine braking will be enabled.

(d) Using the "3", "2", and "L" positions

The "3", "2", and "L" are used for strong engine braking as described previously.

With the selector level in "3", "2", and "L", you can start the vehicle in motion as with the lever in "D".

With the selector lever in "3" or "2", the vehicle will start in first gear and automatically shift to third or second gear.

With the selector level in "L", the transmission is engaged in first gear.

NOTICE

- Be careful not to over-rev the engine. Watch the tachometer to keep the engine rpm from going into the red zone. The approximate allowable speed for each position is given below for your reference:

"3" - 152 km/h (94 mph)
"2" - 98 km/h (60 mph)
"L" - 54 km/h (33 mph)

- Do not continue hill climbing or hard towing for a long time in "3", "2", and "L" position. This may cause severe automatic transmission damage from overheating. To prevent such damage, "4" position should be used in hill climbing or hard towing.



Frankly, I'm confused as to what I can do with the 423L positions. Can someone enlighten me?
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Old 07-18-2008, 07:55 PM
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Re: Corolla 07 Coasting on Neutral?

Quote:
Originally Posted by AlphabetBackward View Post
Frankly, I'm confused as to what I can do with the 423L positions. Can someone enlighten me?
DFCO is a function of engine management. Under certain conditions (engine at operating temperature, foot off the gas, trans in a forward gear), the automatic transmission will remain locked to the engine and the fuel injectors are "shut off". This will occur until the tach falls to somewhere between 1100 and 1400rpm (depending on make/model/engine). The idea of downshifting is to keep the revs up as road speed falls so that the engine remains in DFCO. Downshifting to 4, then 3, and so on, will apply a clutch or band in the transmission to lock the engine to the output shaft in order to provide engine braking. So a lower gear will raise engine speed and slow the car faster. And the higher engine speed, if it is above the threshold for DFCO, will keep the no-gas glide going.

It's probably more work that it's worth for daily driving from light to light, but when slowing as you reach a clump of traffic, it can give you that extra few hundred feet of forward travel without burning any gas.
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Old 07-18-2008, 07:56 PM
AirGibson AirGibson is offline
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Re: Corolla 07 Coasting on Neutral?

Quote:
Originally Posted by MaxxMPG View Post
On page 2-28 of my car's owner's manual, it says, "NEUTRAL (N): In this position, your engine does not connect with the wheels. To restart when you are already moving, use NEUTRAL (N) only. Also, use NEUTRAL (N) when your vehicle is being towed." (bold emphasis added). This states "already moving", shifting to N to restart, and then... They don't say, but shifting to Drive would be the logical next step. If not, they would say, "Stop the vehicle, restart, shift to drive, and take off". Will repeated N-D shifts cause wear long-term? If it did, I'm sure they would find a spot among the 438 pages to add the paragraph, "Do not do this frequently, or you could damage your transaxle. This damage would not be covered by your warranty. You or your passengers could be injured or killed by being crushed under the weight of transaxle repair invoices." etc etc.
In my 2004 Mazda 3i (4 door sedan, 2.0 Liter, automatic) owners manual, I see this:

WARNING: Shifting into N while driving is dangerous. Engine braking cannot be applied when decelerating which could lead to an accident or serious injury. Do not shift into N when driving the vehicle.

CAUTION: Do not shift into N when driving the vehicle. Doing so can cause transaxle damage.
Now I'm generally of the opinion that the owners manual will recommend against pretty much everything in order to cover their asses, much like you indicated above. But the specific warning against transaxle damage worries me. It's not talking about towing or FASing, but simply shifting to N while driving. Unfortunately, they don't give any specifics at all about how exactly it might be damaging anything.

If I ever do it, it feels smooth as butter, but again, that warning that I hear from everyone (including the manual) has me wondering. This is why I generally urge "moderation" where automatic Neutral shifting goes because I just don't get the feeling this issue is as clean cut as we might like. I would love to know if this is, in fact, misinformation because I would gladly try P&G techniques in this automatic if it is not damaging anything. I guess I'll try to find the exact tranny model for that car and any specs for it.
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Old 07-18-2008, 08:03 PM
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Re: Corolla 07 Coasting on Neutral?

I just started doing some ice on coasting in my minivan with 267,000 miles on it.
If this is bad for my old tranny it wont take long to find out!
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