xFistsClenchedx

I have been wondering, is it better to shift into neutral from drive when at a stoplight when driving an automatic? It seems to me that it would be easier on the tranny, but maybe it isn't. I didn't see it covered in the manual.

kskim20

just leave it in D and keep your foot on the brake man...no need to put extra wear on the tranny

ack154

iTrader: (7)

If anything you're shifting unnecessarily and it would create even more wear on the trans. Just leave it in D.

IH8ONYU

also, coasting in gear uses less gas then coasting in neutral..

draxcaliber

dammit guys, it's an AUTOMATIC TRANSMISSION! all you do is tell it if you want to go forwards, backwards or park and press the gas or brake pedla accordingly.

you do not shift to neutral unless the throttle jams open and you can't stop the car, then you shift it into neutral disengage the tranny.

also, you do not shift to neutral to save gas. you leave it in gear, one, because it is the law (look it up, cars are required to be in gear at all time), and 2 because when you're coating in gear, the ecu cuts off fuel to the engine to make it engine brake, thus you use no gas, while rolling to a stop. if you put the car in neutral, the ecu has to start idling, which means it is using fuel to idle, instead of not sending any fuel.

xFistsClenchedx

I was just wondering if it was better at a stoplight. To me it seems like it would be easier on everything if it was in neutral when stopped but I wasn't sure. The engine sounds less strained when idling in neutral than when stopped in D. Usually I leave it in D, but was just curious.

XD40tC

Does it really? For some reason my grandpa shifts into neutral when at a light lol. I found it hilarious but didnt say anything.

ack154

iTrader: (7)

Yup... in gear is best for coasting.

SiZzOuRcE

I was told that shifting a car into N was worse for the tranny because when you are in gear, the tranny is getting gear oil to lube it, but when its in N, it doesn't need it as its not going anywhere. When your coasting, and shift into N, your still driving but no gear oil is coating the gears . . . which is bad.

buickid

Basically, if the engine is running, the front pump is being turned by the engine. This is what is lubricating the gears. So even in neutral, its still being lubricated, as long as the engine is on.

Now as far as shifting into neutral at a light....
An auto trans is a long series of planetary gear sets for the most part. When you shift into a gear, the transmission is clamping down on a planetary gear set with a clutch band to stop it from turning. Every time it shifts, or goes into a gear from neutral, its activating a clutch band. When you stop at the light, the clutch band is still tight and the trans is still in gear. The reason why your engine doesn't stall out like a manual is the torque converter. Its like a fluid coupling designed to give slippage.
So when you shift into neutral, a planetary set start turning in the trans. When you go back into drive, the clutch bands need to clamp down, slowing the gear set from x RPMs down to 0, thus wearing a tiny bit of material off the friction pads on the clutch band. Does it really matter? Maybe. You're wearing about the same amount of material as when you shift into drive from a stop. On the other hand...

This sensation of the engine sounding strained is the car operating normally. Going back to the torque converter, its job is to provide slippage between the transmission and engine, except when you reach cruising speed and the converter locks up. At the stoplight, the transmission's output shaft reaches 0 RPMs, while the engine is still trying to turn it's idle RPMs, say 750 RPMs. In neutral, there is very little resistance on the engine, so it will turn pretty close to 750 RPMs. In gear, stopped, the engine is working to turn the torque converter against a stopped transmission. Since the torque converter is stopped and providing resistance, the engine RPMs will drop, say around 650 RPMs, and the ECU may increase the throttle opening a small amount to try and maintain idle RPMs. Now, the energy being produced by the engine has to go somewhere, so it turns into heat in the torque converter. But heat is bad right? Yes, but the transmission was designed for take normal amounts of heat, and idleing in gear is normal. What isn't normal, and leads to excessive heat are things that give heavy load. The reason why towing packages come with transmission coolers is the added slippage. When you tow a heavy load, you use more RPMs and it takes longer for the vehicle to reach your desired speed. This means more slippage and more heat. The transmission cooler helps to expel this heat. Climbing serious hills can also lead to excessive heat. If the transmission is in 4th gear and you're going 40MPH uphill, you can bet your torque converter isn't locked up, and there is a lot of slippage going on. You can tell the torque converter is locked up in the xB, at 60 MPH the engine RPMs should be around 2250 while locked. Under passing/merging situations, giving it a little throttle will cause the torque converter to unlock, thus bringing the torque converter's torque multiplication characteristic into play. This allows you to accelerate quicker. If you really mash the pedal, the engine may drop down into 3rd gear, for greater torque, or even 2nd gear, if thats not redline. Ok, back to slippage. So when you're going up a hill, and you know the torque converter is unlocked, and the RPMs are really low, you know that the transmission is using the torque converter to multiply the torque through slippage, generating excessive heat. Hopefully the TCM (transmission control module) would have downshifted into a lower gear, but maybe you're right on the edge of the parameters for a downshift. What you do is put your transmission in the next lower gear manually, to use the GEARING's torque multiplication characteristics instead of the converter. Result is less slippage and the engine will probably be closer to it's peak torque range. Also, if the transmission is "hunting" for gears, ie. repeatedly up and downshifting, command it into the lower gear to save wear on your clutch bands, which as we learned earlier are repeatedly engaging and disengaging.

Ok, so I think I covered way more then this topic's intent, but thats transmission 101 for you. Note I am not a certified mechanic nor engineer, but I have a pretty good informal education of automobiles. All of my advice maybe taken with a grain of salt if you wish, I will take no offense, but to the best of my knowledge, the information contained herein is accurate and true for the majority of production passenger vehicles. I only ask that you don't flame me for something that may be incorrect, but rather present me with facts and evidence.
-Trevor

t8legos

Thank you. I found this interesting and informative.

A-snell

iTrader: (4)

WHAT?? that will make the engine "Race" and red line...
great way to ruin an engine..

CIONIDE

iTrader: (1)

Better to blow up the engine than try to drive a car with an uncontrollable wide open throttle.
My brother had the throttle stick at wide open on a Toyota Corolla wagon 25 years ago, and sailed across a T-intersection, up a curb, across the lawn, and crashed into a house. Bro was fine, but Mom was ____ed (her car). Fortunately the police found the throttle (carb) stuck in WOT; and nobody else was in the intersection, on the sidewalk, or playing in the front yard. That one could have ended in tragedy, instead of the valuable lesson learned to throw it into neutral.

A-snell

iTrader: (4)

I had a 75 Mercury Marquis. "BIG YELLOW BOAT" of a car. 440 under the hood. I was street racing with 5 of my friends in the car with me. we got up to 60 in town, when the throttle stuck open. next thing I knew we were doing 95+.... I threw it into "N", but the engine just reved to red line. I dropped it back into "D" and turned the key off, but NOT ALL THE WAY TO "LOCK". lost power steering and power brakes, but was able to stop the car. NOW, not sure if turning the key off will work on the xb2 on-a-counta the ELECTRIC power steering, but that is what I would do BEFORE putting it into "N".

CIONIDE

iTrader: (1)

Equally good solution, but most people will be able to throw it into neutral faster, and with less possibility of accidentally locking the steering by turning the key too far. Congrats on making the right move, and executing it properly. Most people are under way too much stress in that situation to accomplish what you did.

A-snell

iTrader: (4)

yeah. both solutions are right, but the question you have to ask yourself is, Am I strong enough to steer and apply brakes the car with no PS or PB? if not then put it in "N".

CIONIDE

iTrader: (1)

Especially a tough mental process when you're under full acceleration and headed into a T-intersection.

A-snell

iTrader: (4)

true.. when my Merc went crazy all my friends started screaming... (only cause they were ALL girls) ;) It was very scary.

buickid

Perhaps turn it to ACC, put it in neutral, then put it back to ON? Since we have electric power steering, it'll assist even if the engine is off, if the key is in ON (try it, go on a small hill, put it in ON, roll down slowly while turning the wheel, it takes a couple of seconds but the PS kicks in). Plus you have enough vacuum left in the booster for at least 2 hard stops

A-snell

iTrader: (4)

hmmm nice....