The Straight Dope

Go Back   Straight Dope Message Board > Main > General Questions

Reply
 
Thread Tools Display Modes
  #1  
Old 01-03-2001, 12:02 PM
poohpah chalupa poohpah chalupa is offline
Member
 
Join Date: Jun 2000
Location: Calif: Gateway to Oregon!
Posts: 1,140
Oboy. This is an embarassing question:
All my adult life, I've driven a car with manual tranmission. Just bought an automatic.
First: there's a button I can press on the stick that'll shift me into overdrive. What does this do exactly? What are the advantages/disadvantages of overdrive? Power vs. Mileage?
Second: adjacent to the "Drive" setting, there's the numbers "1" and "2"...when would I need to use these? Is this first and second gear? Why would I need these, unless...
Third:...there's a way to push/roll start my car? If I wanted to and if this is what these settings are for, how do I accomplish this? Start in neutral, then suddenly throw it into first?

I feel like such an idiot for not knowing all of this, but quite honestly, I've never needed to know this until now (sorta like the time a district manager came into my store and asked me to make coffee for him. I told him that I didn't know how. He freaked out and went into hysterics about it. Not being a coffee drinker myself, it was just never ever necessary for me to know this procedure...I can't make a martini either).

A little help, please...?
Reply With Quote
Advertisements  
  #2  
Old 01-03-2001, 12:12 PM
bare bare is offline
Charter Member
 
Join Date: Sep 2000
Location: Northern Idaho
Posts: 1,342
For nearly all driving situations all you will need is drive. The overdrive is for long stretches on a flat highway and first and second gear are for when you want to override the automatic features of your automatic transmission for more power.

All this information should be in your owners manual. If you did not get one with the car you can get one from any dealer.
Reply With Quote
  #3  
Old 01-03-2001, 12:21 PM
Coldfire Coldfire is offline
Charter Member
Charter Member
 
Join Date: Jul 1999
Location: Near Amsterdam, NL
Posts: 15,973
The overdrive basically is a top gear, aimed at low revs, and consequently better mileage. It's useless when accelerating or climbing, since the engine is NOT at its peak torque at these lower revs. Also, an overdrive only really works with a sufficiently powerful engine. Not that the average American car lacks power

You can't push-start an automatic, as far as I know.
Reply With Quote
  #4  
Old 01-03-2001, 01:06 PM
kunilou kunilou is offline
Charter Member
 
Join Date: Apr 1999
Posts: 17,833
I was told once you could push start an automatic, but it had to be rolling at something like 25 mph. Considering you'd have no power steering or brakes, rolling at that speed would be dangerous, even if you could sustain it long enough.

Unlike a manual transmission, the gears are there to limit what the car can do. In an automatic transmission, first gear, second gear and drive all mean your transmission won't shift PAST those gears, not that you can start out in them (as with a manual). That's effective if you're rolling down a long hill, or on slick pavement when too much power might make the wheels slip.

You lock out overdrive to make sure your transmission doesn't have to shift back to the power gear. The typical example is when you're in heavy traffic, or on a hilly road, between about 35-45 mph. The transmission wants to shift into the higher gear, but every time you step on the pedal, it downshifts back into drive. Locking out overdrive keeps the car in drive and eliminates the downshifting.
Reply With Quote
  #5  
Old 01-03-2001, 01:07 PM
Enos Strate Enos Strate is offline
Guest
 
Join Date: Aug 2000
I've always driven manual transmissions, too, but it is my understanding that:
First: what Coldfire said.
Second: your automatic tranny probably has 3 gears plus overdrive. If you have it in 1, then the highest gear that it will go to is 1st. If you have it in 2, the highest gear that it will go to is 2nd. If you have it in Drive, it will go through all 3 gears as needed. You would normally only use 1 or 2 if you are hauling a trailer or something and needed the engine to rev higher to get moving, or if you were going down a steep hill and wanted to use the engine to brake with.
Third:what Coldfire said.
Reply With Quote
  #6  
Old 01-03-2001, 01:13 PM
DonJuanDeMarco3 DonJuanDeMarco3 is offline
Guest
 
Join Date: Dec 2000
I don't think it was made very clear that 1st and 2nd gears are basically for very slick conditions in which you need extra torque, not for going slow. You can but on some models it will ruin the transmission.
Reply With Quote
  #7  
Old 01-03-2001, 01:15 PM
CrankyAsAnOldMan CrankyAsAnOldMan is offline
Guest
 
Join Date: Jun 2000
In defense of poopah, I've read our CR-Vs manual, and it doesn't explain Overdive for crap. I was reding it because my husband was telling me that OD was how to engage 4-wheel drive in our CR-V, and I think he's wrong.

However, it *is* a good idea to read that thing cover to cover. It's amazing what you might never know about your car.

You'll probably rarely use those other gears. I shift down (to 1 or 2) when I'm going down a steep hill and find myself riding the brake, or when it's unsually slippery. I never tow anything, but that would be another time to use it. Your owner's manual will tell you what speeds you need to observe while in those lower gears.
Reply With Quote
  #8  
Old 01-03-2001, 01:37 PM
Gunslinger Gunslinger is offline
Guest
 
Join Date: Jun 2000
3-speed plus overdrive? Amazing, the advances they've made...(I driva a '71 Nova w/2-speed Powerglide auto )
__________________
and then they made me their chief.
Reply With Quote
  #9  
Old 01-03-2001, 01:45 PM
AskNott AskNott is offline
Charter Member
 
Join Date: Mar 1999
Location: Anderson, IN,USA
Posts: 14,071
Here's a few details that haven't already been covered. The overdrive is a final-stage overrunning device at the tail end of your transmission. It's a tricky set of planetary gears which makes the driveshaft run faster than the output shaft of the transmission. The engine runs slower in OD, so you save gas. However...when you take your foot off the gas, the OD will freewheel instead of letting the engine slow you down. On a long downhill, that's dangerous. All your slowing will be handled by the brakes, which will heat up and become useless after a while (the brake fluid boils.) Another however...if you're hauling a big trailer, the OD might keep the engine at a gas-saving speed when you really need the power of a higher engine speed to haul that big cabin-cruiser. That's not good for the engine.
MOST of the time, you can keep the shifter in top gear with the OD engaged, and the machine will make all the right decisions for you. You may find that boring, but if you try to play Stirling Moss by blipping up and down through the gears, you'll waste gas, and you might risk hurting the automatic clutches inside the transmission.
__________________
"You know what they say about sleeping dogs; you can't trust 'em." --Oliver Faltz
Reply With Quote
  #10  
Old 01-03-2001, 01:49 PM
jeel jeel is offline
Guest
 
Join Date: Oct 2000
I used to work in Automatic Transmission design at one of the Big 3. Here's what I know.

First, What AskNott said...and......

OD--saves gas, and good for flat driving where wheel torque requirments are low. This means that the vehicle will shift 1-2-3-4 (in a 4-speed model) and will continue to upshift and downshift as dictated by the shift schedule.

OD-off....Transmission will shift to 3rd gear and will not go past 3rd gear. Provides engine braking for downhills and more torque at wheels for uphill driving.

Manual 2. In the transmissions I worked on, Manual 2 means, the vehicle will operate in 2nd ALL the time. Even if you stop and start again. If you are moving when you engage manual 2. The vehicle will shift into second at a safe vehicle speed and engine speed.

Manual 1. The transmission will stay and start in 1st. Same thing as 2...just stays in 1st. Again, the vehicle will wait for a safe downshift speed if the vehicle is moving.

And I have never heard of a way to push start an automatic...being that I think you would need fluid pressure to get the wheels to turn the engine. But I could be uninformed on this.
Reply With Quote
  #11  
Old 01-03-2001, 02:24 PM
ElvisL1ves ElvisL1ves is offline
Charter Member
 
Join Date: Jul 2000
Location: New England
Posts: 33,269
AskNott and Jeel, among others, are right. The only remaining question is about push-starting an automatic. That cannot be done at low speeds because there is no direct mechanical connection between the engine and wheels. Power goes through a torque converter that is usually compared to 2 fans facing each other - if you switch one on, the air flow pushing on the other makes it turn, too. In a car, oil is used instead of air, and it recirculates inside the torque converter in a complicated way, but that's the idea. If you start the drive wheels rolling at any reasonable speed, all you'll do is spin the wheel-side "fan" without getting enough torque into the engine-side one to turn the engine over. Theoretically, if you get going fast enough, it's possible, but you still be safe in trying it. With a manual, instead of a torque converter, there's a clutch consisting of 2 friction disks that mash into each other when engaged. That arrangement allows enough torque to get into the engine to crank it.
Reply With Quote
  #12  
Old 01-03-2001, 02:58 PM
ElvisL1ves ElvisL1ves is offline
Charter Member
 
Join Date: Jul 2000
Location: New England
Posts: 33,269
I should add that recent automatics (in the US, anyway) generally have devices that do mechanically lock the 2 sides of the torque converter, whenever the electronic doohickeys conclude that you're at a constant highway speed. The lockups eliminate power losses due to torque converter slippage and improve mileage a bit.
Reply With Quote
  #13  
Old 01-03-2001, 05:03 PM
Telemark Telemark is online now
Charter Member
 
Join Date: Apr 2000
Location: Hub of the sports world
Posts: 15,387
More uses for gears other than D

If you are going down a steep hill, especially if you have a heavily loaded vehicle, you will learn to love the 1 and 2 positions of your automatic tranny. It's much better to use the tranny on *prolonged* downhills than to use your brakes, which can overheat and boil your brake fluid. By preventing the tranny from upshifting it keeps the revs high and increases the engine braking.

Also, some luxury cars have a winter driving mode, that starts the vehicle in second, rather than first. As I understand it, this is to limit the torque to the drive wheels when starting out and prevent slipping. I imagine this is more common on powerful rear wheel drive cars.

Finally, unless you are going down long hills where you need some engine braking, or driving around town at *just the right speed* that your tranny is hunting up and down to overdrive, leave the OD button on all the time. There's no reason to deactivate it otherwise.
Reply With Quote
  #14  
Old 01-03-2001, 06:10 PM
Coldfire Coldfire is offline
Charter Member
Charter Member
 
Join Date: Jul 1999
Location: Near Amsterdam, NL
Posts: 15,973
Quote:
Originally posted by jeel
Manual 2. In the transmissions I worked on, Manual 2 means, the vehicle will operate in 2nd ALL the time. Even if you stop and start again. If you are moving when you engage manual 2. The vehicle will shift into second at a safe vehicle speed and engine speed.
Are you saying it will then even accelerate from a full stop in two?

Most of the automatics I've driven were either European or Japanese (a few Americans). From what I recall, "Manual 2" stands for "using the lower two gears", not "using only second gear".
Reply With Quote
  #15  
Old 01-03-2001, 06:19 PM
jeel jeel is offline
Guest
 
Join Date: Oct 2000
Quote:
Originally posted by Coldfire
Are you saying it will then even accelerate from a full stop in two?
Yup.
Reply With Quote
  #16  
Old 01-03-2001, 06:22 PM
Gunslinger Gunslinger is offline
Guest
 
Join Date: Jun 2000
Quote:
Originally posted by Coldfire
[BFrom what I recall, "Manual 2" stands for "using the lower two gears", [/B]
That's what the owner's manual of my late Wagoneer (MoPar 727 3-speed auto) said. I dunno about Ford trannies, though...
Reply With Quote
  #17  
Old 01-03-2001, 07:01 PM
Coldfire Coldfire is offline
Charter Member
Charter Member
 
Join Date: Jul 1999
Location: Near Amsterdam, NL
Posts: 15,973
Could that be an American thing then?
Reply With Quote
  #18  
Old 01-03-2001, 08:25 PM
SSgtBaloo SSgtBaloo is offline
Guest
 
Join Date: May 1999
YMMV

It might help if you told us what you drive, since different manufacturers have their own favorite ways of doing things. Also, there are sometimes different transmissions available in the same model, so one might have a 3-speed with (or without) an overdrive gear, and another might be a 4-speed with 4th having an overdriving ratio.

I drive a 1994 Dodge Caravan, and I'm still trying to figure out just how it's supposed to work ("put it in drive and just go" works just fine 99% of the time). I have a column-mounted gear selector, and can choose from P-R-N-D-2-1, plus I have an overdrive lockout button (ODLB) located on the dash. If the ODLB is not activated, the transmission will start in first, then shift through second, then third, then (finally) to overdrive. In my vehicle, I suspect this is actualy an extra set of gears at the output shaft of the transmission (as described above). Some cars just have an extra gearset or so to give a fourth or even a fifth ratio, and gear them to drive the output shaft[s] faster than the input from the engine.

If the selector is in "2", it starts in second, but will shift to third (possibly the overdrive -- I don't lock it out most times). When I select "1", it starts in first and shifts to second (once again, maybe the overdrive). My van isn't quite like new and I'm not certain if it's really supposed to work this way, and since the owner's manual is kind of vague about how it operates, I can't be sure. From perusing the manual (it's different in many cars) I do find that they recommend I leave the ODLB alone unless I'm driving in hilly/mountainous terrain or traffic where the transmission is frequently shifting in and out of top gear. Locking out the overdrive will keep it from shifting into overdrive.

As far as driving on slippery surfaces is concerned, what you are ideally trying to do by "downshifting" isn't to put more torque to the road, but less. Starting in second, rather than first, puts less power to the slippery surface, reducing the chance that one tire or the other will slip. Unless you have a limited slip differential, a slipping tire means all the power from your engine is wasted turning he wheel that's slipping -- no useful power goes to the tire that still has traction. Reducing the power going to the wheels by starting in a higher gear reduces the chance of one wheel slipping. This allows you to start moving sooner with less drama than in a lower gear. When starting from a stop on a slippery road surface, you don't want to start in first, but second. Leaving the car in "D", you'll start in first gear (as will shifting it to first).

Some of you manual-only people might protest that starting out in a taller gear than normal will cause the engine to "lug". Don't worry about it. A car with an automatic transmission can't lug its engine. Otherwise, you'd have to shift into neutral whenever you came to a stop to keep the engine from dying (I've owned cars that worked like that, but it wasn't the transmission's fault).

~~Baloo
Reply With Quote
  #19  
Old 01-03-2001, 11:03 PM
Balthisar Balthisar is offline
Charter Member
 
Join Date: Nov 2000
Location: Nanjing, China
Posts: 8,965
FYI...

Quote:
Originally posted by ElvisL1ves
I should add that recent automatics (in the US, anyway) generally have devices that do mechanically lock the 2 sides of the torque converter, whenever the electronic doohickeys conclude that you're at a constant highway speed. The lockups eliminate power losses due to torque converter slippage and improve mileage a bit.
You should see this listed on the original window sticker of the car -- it will be listed as a "lockup torque converter." This is generally only used on cheap cars with 3-speed transmissions. I guess they figure people who buy cheap cars need to save money on gas. Anyway, it still serves as a type of quasi-overdrive. I think this is how my Ranger works (I'll investigate); I do have an "over drive off" option.

"Better" American cars seem to have 4-speed transmissions, with no silly nonsense about overrdrive or lockup torque converters. My Bonnie has four real gears that you can only barely feel shifting. Not having a lockup torque converter or a "true" overdrive is a blessing, in that there is no extra hesistation when you need the power -- you step on the petal and it instantly goes to the gear it needs to. There's not winter driving mode; I have some type of traction control that seems to be controlled by the transmission (my old '94 Bonnie used ABS system for traction control, and didn't work too well).

From my experience, I would recommend that you always look for a 4-speed withOUT the overdrive or the lockup torque converter. Obviosly, that goes only if your needs are similar to mine -- I don't pull anything, and I like to get enjoyment out of driving. The Ranger I mentioned above is NOT fun to drive, and I think it's the transmission's fault (hey, it's a commuter car).

Tschuess.
__________________
---
If you want to discuss cannibalizing black people, probably the best place for that is the BBQ Pit.
-- Colibri
Reply With Quote
  #20  
Old 01-03-2001, 11:17 PM
Zor Zor is offline
Guest
 
Join Date: Jan 2000
A quick question to all the car buffs: can you shift from drive into overdrive/1/2 while going at any speed? Having driven an automatic for quite a while, I only put my hand on the gears when I start or park my car. I imagine if I find myself running down a steep hill one day I might want to shift to 1/2, but then do I have to come to a full stop first?

Thanks!
Reply With Quote
  #21  
Old 01-04-2001, 12:11 AM
Badtz Maru Badtz Maru is offline
BANNED
 
Join Date: Aug 2000
Location: Dallas, Texas
Posts: 5,665
Quote:
I don't think it was made very clear that 1st and 2nd gears are basically for very slick conditions in which you need extra torque, not for going slow.
I was taught that on slick roads you wanted to use a gear higher than you normally would, to reduce torque and thus the chance of a spin-out. Not much you can do about that with an Automatic transmission, though if the roads are extremely slippery and you aren't going too far, I heard that it's advisable to put the parking brake on a couple of clicks
Reply With Quote
  #22  
Old 01-04-2001, 01:07 AM
Mr2001 Mr2001 is offline
Guest
 
Join Date: Dec 1999
Zor:
Quote:
A quick question to all the car buffs: can you shift from drive into overdrive/1/2 while going at any speed?
Yes. The car may decide not to shift down if you're going too fast, though.

You can also shift up (1->2->D) at any time, without pressing the lock button or pulling the lever. I've found this useful in situations that closely resembled stop-light drag racing, but of course this only took place in designated legal areas.
Reply With Quote
  #23  
Old 01-04-2001, 06:06 AM
Coldfire Coldfire is offline
Charter Member
Charter Member
 
Join Date: Jul 1999
Location: Near Amsterdam, NL
Posts: 15,973
Quote:
Originally posted by Badtz Maru
Not much you can do about that with an Automatic transmission, though if the roads are extremely slippery and you aren't going too far, I heard that it's advisable to put the parking brake on a couple of clicks

I'd advise against that! Strongly.
You'll wear out your parking brake drum (in case of rear disk brakes), or your entire rear breaking system (in case of rear brake drums).
Reply With Quote
  #24  
Old 01-05-2001, 06:55 AM
sewalk sewalk is offline
Guest
 
Join Date: Apr 1999
YMMV is definitely the watchword when it comes to settings beyond D. On a Mercedes-Benz 5-speed automatic, there is no 1st gear setting, but putting the selector in 2 will tell the transmission to downshift to 1st gear as soon as the engine speed is low enough to do so. When accelerating, slapping the lever up to 3 will let the transmission shift into 2nd gear and you can then put the selector back into 2 to hold 2nd gear. Further upshifts will occur as the selector and engine speed permit. On most American passenger car automatic transmissions (I say most but every one of the dozens and dozens of cars I've driven behave this way), the selector sets the highest gear the transmission will use. When I got my 1984 Hurst/Olds, I assumed that the special shifter would allow me to choose what ever gear I wanted, when I wanted it. Not so; it merely acted as a more precise version of the typical automatic shifter (i.e. slap a different lever for each upshift/downshift). I currently have a Japanese car with an automatic transmission; it behaves just like any American car in that respect.
Reply With Quote
  #25  
Old 01-05-2001, 02:53 PM
jeel jeel is offline
Guest
 
Join Date: Oct 2000
Quote:
Originally posted by Balthisar

You should see this listed on the original window sticker of the car -- it will be listed as a "lockup torque converter." This is generally only used on cheap cars with 3-speed transmissions. I guess they figure people who buy cheap cars need to save money on gas. Anyway, it still serves as a type of quasi-overdrive. I think this is how my Ranger works (I'll investigate); I do have an "over drive off" option.

"Better" American cars seem to have 4-speed transmissions, with no silly nonsense about overrdrive or lockup torque converters. My Bonnie has four real gears that you can only barely feel shifting. Not having a lockup torque converter or a "true" overdrive is a blessing, in that there is no extra hesistation when you need the power -- you step on the petal and it instantly goes to the gear it needs to.
The overdrive and lock-up on the torque converter are not silly nonsense. The TC lock-up helps improve not only fuel efficiency but also helps the transmission itself to operate cooler and more efficiently. The OD and TC lock-up also help engine life by allowing it (the engine) to operate at a lower RPM at cruising speed on flat highway driving conditions. BTW, many vehicles come with both OD and TC lock-up on the same transmission. And those aren't only the cheap ones with 3 gears. Many of the high torque diesel engines, when not loaded down to full capacity require extra OD ratios to keep from over revving the engine at highway cruising speeds. TC lock-up helps in that situation.

A properly calibrated locking TC should not produce any hesitation in gear change when the vehicle needs to shift. The two shift schedules should be independent of eachother. And the TC lock-up is usually dependent on vehicle acceleration as well as speed and throttle position, so as soon as the vehicle comes to a hill, for example, the TC should unlock, allowing the TC to multiply engine torque giving the vehicle the required wheel torque to make it up the hill or past whatever other hindrance.

BTW. I bet the 4th gear on your Bonneville has an OD ratio. What you meant by four "real" gears is what I do not understand. Unless people consider OD gear ratios as imaginary.
Quote:

The Ranger I mentioned above is NOT fun to drive, and I think it's the transmission's fault.

What size engine do you have? I'm not saying the transmission is not at fault, it may be calibrated poorly. But I'm just curious as to what engine is in your truck.

jeel
Reply With Quote
  #26  
Old 01-05-2001, 09:17 PM
Balthisar Balthisar is offline
Charter Member
 
Join Date: Nov 2000
Location: Nanjing, China
Posts: 8,965
Quote:
Originally posted by jeel
...lotsa stuff...
You're right about everything you said. But I think I mentioned that what I was saying was for drivers like me. Unless gas hits $2 again before I get a pay raise, I don't really care what it costs for gas. There's no need for me to have SILLY (yes, in my case, SILLY) little devices to try try get get an extra 2MPG out of my fuel use. I can't imagine that there aren't a LOT of people who drive like I do.

As for the other points, I concede your point again, but trucks, cargo, lots of weight, etc., doesn't apply to vehicles meant to be driven for pleasure as much as transportation.

Ah, the Ranger... it's a tiny little 4 cylinder, and I don't even know how small it is. I didn't look when I bought it -- all I cared about was getting the cheapest econobox I could for work (uh, despite this statement, I don't mean for the price of gas). So, to a large degree, the engine has a lot to do with how un-fun it is to drive. But the transmission SLAMS when I nail it, and it's still very, very noticeable shifting when I drive "normally." When the vehicle is in overdrive and I step on the gas, it takes a considerably longer to disengage and engage in a low gear than the other gears, or my car. I'm assuming that this is because it's not a "normal" 4-th gear, it's an overdrive gear.

My statements about "real" fourth gear versus an overdrive gear reflects my admittedly ignorant knowledge that there are two different types of overdrive systems (plus lockup torque converters). Those that have a "real" fourth gear that is like any of the other gears, and those that drive in third with a supplemental gear somewhere between the driveshaft and the output shaft.

For the record, I am an engineer in one of the big three, but I don't know anything about the design of transmissions. I *DO* know the types of transmissions I like to drive!
Reply With Quote
Reply



Bookmarks

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is Off
HTML code is Off

Forum Jump


All times are GMT -5. The time now is 11:20 AM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.

Send questions for Cecil Adams to: cecil@chicagoreader.com

Send comments about this website to: webmaster@straightdope.com

Terms of Use / Privacy Policy

Advertise on the Straight Dope!
(Your direct line to thousands of the smartest, hippest people on the planet, plus a few total dipsticks.)

Publishers - interested in subscribing to the Straight Dope?
Write to: sdsubscriptions@chicagoreader.com.

Copyright 2013 Sun-Times Media, LLC.