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Shifting on an automatic-- have to release accelerator?


DriverEnthusiast
07-03-2003, 07:45 PM
I don't shift on my automatic too often, but every once in a while I'll do so. My question is when I do this, do I have to let off the accelerator the way you do so when pressing in the clutch in a manual transmission? Or can I shift without chaning the pressure I have on the gas?

Thanks

PWMAN
07-04-2003, 07:54 PM
Keep foot on accelerator, it will shift like normal. Just like you had the tranny in drive.

buymeabmwm3
07-10-2003, 08:21 AM
When driving my brother's automatic Merc Cougar, I always lift off the throttle when I shift. Why? Because engine revs have to drop to move to the next higher gear. If you stay on the throttle in 2nd, then shift to 3rd, the torque convertor has to work a lot harder to link up the higher speed of the engine to the lower speed of the transmission. Basically, by not lifting off, you much more spinning in the torque convertor, and therefore much more heat. And heat is the worst thing for your transmission. It is the primary limit on transmission lifetime. Rev matching betwene the engine and the gears is always a good idea. Guys that drive manuals do it all the time, automatics should do it too. You will be faster, smoother, and most importantly, your tranny will thank you.

DriverEnthusiast
07-10-2003, 11:36 AM
Originally posted by buymeabmwm3
When driving my brother's automatic Merc Cougar, I always lift off the throttle when I shift. Why? Because engine revs have to drop to move to the next higher gear.

Does this also apply to shifting down?

The last time I shifted in my automatic was on the freeway. I was going maybe 60 in the top gear, and without lifting my foot off the gas, dropped the transmission into "3". Is that a bad thing? Should I also let off the accelerator in situations like that?

buymeabmwm3
07-10-2003, 11:47 AM
Your intuition is correct. You should do the exact opposite in downshifting - hold the throttle wide open. This would correspond to downshifting a manual to overtake a slower car. At any given speed, revs must increase when shifting down, so you should plant your foot. Note: All of this does not mean the car won't shift if you don't have the right throttle placement. It will. But lifting the throttle on upshift, and opening the throttle on downshift is the best way to prolong your transmission/torque convertor life.

BeEfCaKe
07-10-2003, 01:19 PM
Dude that makes no sense... what you said for manual is true...

but it can't apply to autos... cause there is no intermediate NEUTRAL area, where you do the "rev-matching".. ok I know there is Neutral on auto... but what is its location? on typical cars.. it is

N
OD
D
2
1

Now.. if you're down shifting.. plz tell me how u're going to go from say.. OD->D, but go through N also, without passing thru OD twice?
Now without this neutral, how is this rev-matching going to work?... say D->2
You're going to "rev-match" just prior to downshift? or after downshifting? Either way, it ain't helping the tranny..
On a manual, 3->2, you would engage clutch, do the rev matching, then shift down.. now THIS would help... but I don't see how this would work for auto..

DriverEnthusiast
07-10-2003, 02:36 PM
The situation I described was simply shifting the transmission from OD to D without going through Neutral.

buymeabmwm3
07-10-2003, 03:01 PM
Beefcake -
Its not really rev-matching like you do in manuals, you are correct. Its just anticipation for what the engine is going to want to do once it has actually changed gears. There is no intermediate shift into neutral as you describe. Say you're doddling along in D, with O/D switched off. In most cars with 4-speed automatics this would correspond to 3rd gear. If you want to upshift to 4th gear, i.e. O/D, then you should accelerate to the approriate speed where you want to shift, back off the throttle, make the shift by pressing the O/D off button or moving the shifter, and then accelerate now in 4th gear. To downshift to 2nd gear, you would want to decelerate in 3rd gear until you wanted to perform the shift, then move the shifter from 'D' to '2' while simultaneously pressing down the throttle.
Here's what would happen with no throttle action. When you upshift from D to O/D, while keeping the accelerator floored, there will be a significant lag in the transmission before it engages the next gear. You will shift the lever, but the transmission will act with a delay. On some cars, such as my Merc Cougar, this delay can be as long as 1 second, which doesn't sound long until you're trying to actually race someone. The reason for this is fairly complex, but its basically the transmission will stumble as it tries to figure out what you are doing. Usually when you floor the accelerator, the transmission is designed to DOWNshift, not UPshift. So it gets confused. Now, how about downshifting. Same thing really. If you're in D, 3rd gear, and you want to drop into 2nd, the normal thing to do is just mash the pedal to the floor. When you do that, the transmission performs an automatic downshift, and you hear the engine suddenly roar as the revs climb. So all you are doing when you "rev-match" as I explained earlier is anticipating this and helping the transmission out. If you just throw the shifter from D to 2 without any added throttle, the car will undergo engine braking. Because now the engine has to work through a smaller gearing, even though the car is still traveling at the same speed. Try it sometime. Drive along in third gear, then without any added throttle, throw it to 2nd. You'll feel the car dive, as if the transmission is trying to drive the engine up to higher revs. In fact, this is exactly whats happening.
So, in the end, all you need to do to make things go more smoothly, is operate the throttle in the direction that is inevitably has to go once the shift is performed. When upshifting, back off the throttle. When downshifting, get into it.

Chris V
07-14-2003, 02:40 PM
:confused:

In 25 years of performance driving, being a driving instructor for SCCA and BSCC on the track, and doing drag racing, AND having both manual and automatic cars as daily drivers, I've never heard such a load of misinformation in my LIFE.

:headshake

DriverEnthusiast
07-14-2003, 03:11 PM
Originally posted by Chris V
:confused:

In 25 years of performance driving, being a driving instructor for SCCA and BSCC on the track, and doing drag racing, AND having both manual and automatic cars as daily drivers, I've never heard such a load of misinformation in my LIFE.

:headshake

Chris V, what are your thoughts regarding shifting an automatic? What was said that was wrong?

v10_viper
07-14-2003, 10:45 PM
With today's engines do the computers in them not match the revs for you?? If I'm crusing down the highway in our Silhouette(minivan) and say I want to pass someone I simply push down on the accelerator and it downshifts for me, why do you need to do it with the gear selector?? I even read this straight out of the manual, it's sensitive to wear if your in cruise control going 60 mph and want to pass, you press down on the accelerator and it downshifts one gear, press down on the gas pedal all the way and it will downshift into second gear above speeds of 40 mph and below like, 80 mph I think. Even when I'm driving with my Ranger that is a manual, since I dont have a tach I dont match revs, it's not really a problem. I mean driving an automatic, if I was going to downshift it to accelerate I'd just press on the gas pedal, why sacrifice an accidental slip into too low of a gear and have my engine over rev on me??

BullShifter
07-20-2003, 12:52 AM
The only time you should be shifting an auto trans is when it has a manual valve body.

Releasing the gas between shifts, LMAO thats dumb.

SupaStealth TT
07-20-2003, 01:28 PM
I would have to agree with Chris V. this sure as hell seams like loads of misinformation. if you're tryin' to downshift in an automatic, you want to press on the gas to get the rpms closer to what its goina be in the next gear, what??? if ya press the gas you're just goina accelerate because its in gear, just like stated before, there isn't a neutral state that you could use for shifting. so you're never goina make it to that rpm because its goina get higher and higher because you're goin' faster. I dunno whatever, lol. :bloated: :eek7:

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