-Filter Forums-
Loading posts...

Automatic gears

Au

Automatic gears

Postby moonmaid » Thu Aug 01, 2013 5:10 pm

Hi,
not quite as lively here :( ---- as the ABC was.

My son recently bought a 1998 Mitsubishi Verada (like a Magna), auto. It's a 3.5L engine.
He doesn't drive over 80km/hr because he's on 'L' plates.

Most of the driving is in a quiet area on 60-80km/hr roads.

Would it be best to drive in 3rd gear instead of Drive?
I haven't got the manual on me but it said that you can drive up to about 100km in 3rd gear I think it was.
Even 2nd gear for this size engine? But say 3rd.

I haven't owned an automatic. He was a rotten driver and couldn't get the hang of the crappy everything in my little old car so did barely any driving then. He's much better now with the Verada.

If the 3rd gear isn't used for this .... what's it for? I can understand the lower gears for going up and down mountains but 3rd is getting a bit high for that?

I told him to use 3rd but he doesn't listen to anything I say of course. (I could be wrong anyway, what? mum wrong?!)

thanks
MM
moonmaid
 
Posts: 122
Images: 1

Re: Automatic gears

Postby Helix » Thu Aug 01, 2013 6:25 pm

Stick it in drive and let the car choose the gears. That's the whole point of an automatic! If he needs third, he can just hit the kickdown and the car will downshift. (But as he's only doing a top speed of 80km/hr, he won't be doing that too often.)

Wikipedia has a quick summary of the whole biz: https://en.wikipedia.org/wiki/Automatic_transmission
At the fringes of civilisation
Helix
 
Posts: 969
Images: 17

Re: Automatic gears

Postby roughbarked » Thu Aug 01, 2013 6:43 pm

Helix wrote:Stick it in drive and let the car choose the gears. That's the whole point of an automatic! If he needs third, he can just hit the kickdown and the car will downshift. (But as he's only doing a top speed of 80km/hr, he won't be doing that too often.)

Wikipedia has a quick summary of the whole biz: https://en.wikipedia.org/wiki/Automatic_transmission



Spot on summary.
roughbarked
 
Posts: 879
Images: 2

Re: Automatic gears

Postby Teleost » Thu Aug 01, 2013 7:07 pm

Yep.

Leave it in Drive. 3rd with a shift lock (usually only found in 4wd autos) is good for reducing torque when driving in mud so you can't spin the tyres.

Holding it back in third at 80 for short periods should not do any damage, but will reduce fuel economy. I wouldn't want to sit in third at 80 for a long time, high revs=more heat and therefore replacement of transmission fluid at more frequent intervals.
User avatar
Teleost
 
Posts: 446
Images: 12

Re: Automatic gears

Postby Teleost » Fri Aug 02, 2013 12:18 am

Something else to bear in mind.

Learning to drive is incredibly complex. The number of things that you need to concentrate on at the same time can be a little overwhelming. When you've been doing it for years, you don't need to think about it so much.

Learing to drive in an auto relieves him of the need to concentrate on the challenges of gearbox and clutch. Once he's got the rest of it down, then put him back in a manual vehicle and work on that. When the time comes for his driving test, doing it in a manual vehicle will be better in the long run. I have a number of staff who are restricted to driving automatic vehicles - It makes life really difficult as I lose a great deal of flexibility when writing rosters. Although it also means that they leave my brand new Hilux alone :)
User avatar
Teleost
 
Posts: 446
Images: 12

Re: Automatic gears

Postby moonmaid » Fri Aug 02, 2013 1:42 am

Thanks for your help everyone.

Yes Teleost, the manual was too much for him. Well, my car anyway, he reckons the driving instructor's manual car was OK.
He's a bit nervous driving (me too! -suddenly veering off the road and stuck on a dirt mound in the bush and no mobile coverage was fun, he jumped up and down on the car to get traction while I reversed out).

The automatic has been a huge improvement. I've just checked websites re: driving a manual if tested in an auto. In NSW you can drive a manual once off red P's --> on green P's without having to re-sit the test. In Vic & ACT once you have a full licence you can drive a manual. I think you need an experienced passenger for some states until you're OK with a manual but no formal thing for nsw/vic/act.

Where are you Teleost? Maybe the staff are able to drive manuals? It seems in WA & Qld you have to sit another driving test.
It should be the same nationwide?

I've just read that you can't get a driver's licence until 18 in Victoria, it's 17 in NSW.

The speed on highways and freeways now is frightening. There wasn't much of that in 'my' day.
moonmaid
 
Posts: 122
Images: 1

Re: Automatic gears

Postby fsm » Fri Aug 02, 2013 12:44 pm

moonmaid wrote:Would it be best to drive in 3rd gear instead of Drive?
I haven't got the manual on me but it said that you can drive up to about 100km in 3rd gear I think it was.
Even 2nd gear for this size engine? But say 3rd.

I haven't owned an automatic. He was a rotten driver and couldn't get the hang of the crappy everything in my little old car so did barely any driving then. He's much better now with the Verada.

If the 3rd gear isn't used for this .... what's it for? I can understand the lower gears for going up and down mountains but 3rd is getting a bit high for that?


99% of the time you should just put the transmission into Drive and let it do its thing. 3rd gear in an automatic is useful when you are travelling downhill for an extended duration. This can help avoid overheating the braking system.

If you deliberately choose to drive in 3rd gear instead of Drive then you will simply waste fuel.
Two + two equals fish.
User avatar
fsm
 
Posts: 462
Images: 146
Location: Central Coast, NSW
Blog: View Blog (1)

Re: Automatic gears

Postby Milieu intérieur » Fri Aug 02, 2013 10:49 pm

Generally the idea of an auto is you let it do its thing, there are a few situations an individual may choose to limit the highest gear the transmission can change up to. The worse that can happen I suppose is you exceed the maximum recommended RPM of the engine for some period and put a rod through the block or do a crank bearing or something similarly expensive [blow the engine], but you'd have to be....... in some way not to hear the engine screaming and/or not see the tacho/rev counter redlining. This can even be done in a manual, like you just had an argument with the partner and drove away insanely. But then the driver may want the other to hear the car scream down the road valve bouncing across the intersection without stopping.

Autos use a kickback on the accelerator [pops the auto transmission back a gear} when you need some serious power [well, in the old days] today additionally they probably have advanced pressure sensors and shaft speed monitors and more to make the decisions for you. Maybe even part of or connected into the engine management system. Never had an auto apart for repairs.

Newer cars have very smooth gear changes [and are smarter], but there are some contexts, say like traversing a bit of a hill with a load behind, in which case limiting what highest gear it may automatically change up to is helpful. You can have more throttle response and more power in reserve, plus less delay because it doesn't have to change back a gear, or so many, particularly maybe important of lower powered vehicles, and as fsm stated you can get more engine brake down hills by keeping it down a gear.

In some cases autos can't make best decisions about gear changes, as they can't predict what is coming next or maybe do what is optimal as whatever changes [can't anticipate]. More though you simply get a few unnecessary gear changes that you don't even notice and they don't matter. For example you're powering up a bit of a hill and it's say in second gear and you decelerate some and it changes to a higher gear and labours some. It does a couple of changes that probably aren't required but it doesn't matter.

But there's nothing to stop anyone driving their auto like a manual, just don't pop it into reverse or park while powering along at speed. Does them no good at all. Last case like that I heard of was a constabulary lady taking a drunk elsewhere - had drunk chap in front passenger seat I understand - who decided to do a few gear changes while going down the highway, which may have included reverse gear.
Milieu intérieur
 
Posts: 241

Re: Automatic gears

Postby moonmaid » Sat Aug 03, 2013 3:53 am

thanks fsm and milieu,

eeks, a drunk in the passenger seat putting it in reverse! Reminds me of when I was in a twin-otter stopping a drunk from trying to open the door mid-flight.

something else ...

In a manual, if I park on a hill (nose facing downhill) putting the gear in reverse will hold the car in place. Same thing by putting it in 1st gear if the bum of the car is the lowest. I never have the manual in neutral with just the handbrake holding the car in place in these circumstances.

Now, with an automatic there is only the 'Park' - which doesn't give the choice of opposing actions.
What's the go here? Does it help putting the automatic into 1st gear or reverse? or aren't you supposed to do that?
(I haven't experimented with his car).
moonmaid
 
Posts: 122
Images: 1

Re: Automatic gears

Postby Teleost » Sat Aug 03, 2013 9:03 am

When you put it in park, there is a pin that clicks in to prevent the gearbox moving - forwards or backwards.

Always put it in park when you are leaving the vehicle.

Similarly you won't be able to start the vehicle unless it is in park. Some older transmissions let you start in neutral but they're pretty rare.
User avatar
Teleost
 
Posts: 446
Images: 12

Re: Automatic gears

Postby Helix » Sat Aug 03, 2013 10:22 am

What Teleost said. Plus newer automatics (some? all? mine, anyway) won't let you take the key out of the ignition if you don't have the car in Park.

(You still need to put on the handbrake, just in case.)
At the fringes of civilisation
Helix
 
Posts: 969
Images: 17

Re: Automatic gears

Postby Milieu intérieur » Sat Aug 03, 2013 10:51 am

Autos have a torque converter instead of a clutch, connects engine crankshaft into transmission/gearbox, it's fluidic coupling arrangement, it starts to drive at maybe around 1000RPM, below that it doesn't couple much at all hence not being able to push start them. That's also why they can roll away if left in any gear except Park. Quarter-mile drag racing vehicles can have a torque converter that doesn't start to drive until the engine gets up around 6000RPM ["high stall" torque converter], for example, which'd make for interesting driving negotiating stoplights around the city I reckon.

Generally you use Park for parking with an auto, and use the handbrake. Generally I don't completely trust Park in autos as they can get damaged.

Manuals generally you use the lowest gears for parking [1st, or reverse is OK], as this way it is hardest for the wheels + vehicle mass on a slope to overcome compression of the engine pistons/cylinders. Vehicles will creep a bit if the handbrake isn't on while on a slope, especially a worn engine that has less compression and/or with a heavy load on or attached to vehicle. Generally diesels have higher compression so the engine is better for parking.
Milieu intérieur
 
Posts: 241

Re: Automatic gears

Postby roughbarked » Sat Aug 03, 2013 7:42 pm

I'm not mechanic, though I am a watchmaker. From memory, automatic gearboxes don't engage in the other gears with the motor unless the motor is running. Maybe this has been changed but I do know that if you park an auto of the older types in drive or the other gears, the car is capable of rolling away and crashing into things. I know this because I have done it. This would be why there is a locking pin in the Park position and why there is a denomination known as Park.
roughbarked
 
Posts: 879
Images: 2

Re: Automatic gears

Postby moonmaid » Sun Aug 04, 2013 1:10 am

Thanks, Park it is. I don't have to experiment with his car.

I'm sure dad is looking down on me laughing. He fixed anything for everybody.

BTW I forgot to mention that I did have a reason for asking about driving in 3rd gear.
When my son drives on the highway sitting on 80km/hr often it seems right at the point where the car wants to
change back a gear and there is that slight kind of sound of the engine struggling a bit in the wrong gear, low revs or something.
moonmaid
 
Posts: 122
Images: 1

Re: Automatic gears

Postby Milieu intérieur » Sun Aug 04, 2013 2:42 am

I gather the exhaust pipe is all good, and engine is in good tune, autos can sound labouring with a bad pipe.
You can run the RPM down lower in any gear with an auto, saves fuel and there's not the usual gear chatter you get with a manual box.

That's one big reason you don't do such low RPMs with manuals, each combustion stroke etc put a slight acceleration and deceleration on the crank shaft [vibration somewhat smoothed by the flywheel on the back of the engine] - "gear chatter".

Autos hardly have much at all other than the torque converter weight spinning around, they hardly need a flywheel because there's not much to chatter.

Probably auto transmissions have pressure sensors and may compare input and output shaft speeds or/and pressures for general selecting of gears [ignoring kickback for a moment], I am not sure, I haven't had to disassembled one and had to repair them. Done a few manual boxes.
Milieu intérieur
 
Posts: 241

Re: Automatic gears

Postby Teleost » Sun Aug 04, 2013 10:01 am

Milieu intérieur wrote:I haven't had to disassembled one and had to repair them. Done a few manual boxes.


Don't!

They're far more complex than a manual box and unlike almost everything else I've ever pulled apart, they don't work just as well with a few bits left over :)
User avatar
Teleost
 
Posts: 446
Images: 12

Re: Automatic gears

Postby Milieu intérieur » Sun Aug 04, 2013 2:24 pm

Keep up the sense of adventure. Generally I get full service manuals with vehicles when buy them, though didn't have one for the last vehicle I rebuilt the motor, had to guess the torque tension on the big-end bearings, but hey hasn't thrown a rod yet.

Last manual box had done at shop they didn't refit the little ball and spring [locker, whatever] on the rail [guessing] for 1st/2nd holds it in place, hasn't bothered me none, though hope they are not floating around inside. Previous to that another manual box done at the shop I tried to turn the output shaft before reinstalling, using a large pipewrench, but couldn't turn it at all [checked it was free], so back to shop and they split it again and sorted it. So, you know, even the experts don't always get it all perfect.

I don't bother with auto transmissions at all, there's guys that specialize for that.
Milieu intérieur
 
Posts: 241

Re: Automatic gears

Postby Wattie » Mon Sep 02, 2013 11:17 pm

Hi all, I agree with everything said. I am a lecturer in plant mechanics and am delivering automatic transmission at the moment.

Even though the learning outcome relates to Autos only we cover as many types of transmission as we can. Over this two week block the students are stripping down and rebuilding a Borg Warner 35 car transmission, five speed Hino truck manual trans, 18 speed road ranger, Spicer clutch on a Cumming Signature 600, Cat 992 split impeller torque converter, Cat D4 transmission complete, Cat 773 Lockup torque converter, Mitsubishi canter clutch (remove and re-fit).

So as everyone has said. Stick to drive and let it do the thinking.
Wattie
 
Posts: 11

Re: Automatic gears

Postby moonmaid » Wed Sep 04, 2013 11:16 pm

You should have a bucket full of left-overs with that lot :)

BTW Thanks Wattie
moonmaid
 
Posts: 122
Images: 1


Return to Automotive

cron